Birds, Water, and Saltcedar: Strategies for Riparian Restoration in the Colorado River Delta

Item Type text; Electronic Dissertation

Authors Hinojosa-Huerta, Osvel

Publisher The University of Arizona.

Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Download date 26/09/2021 15:12:46

Link to Item http://hdl.handle.net/10150/196071 BIRDS, WATER, AND SALTCEDAR: STRATEGIES FOR RIPARIAN

RESTORATION IN THE COLORADO RIVER DELTA

by

Osvel Mario Hinojosa Huerta

______

A Dissertation Submitted to the Faculty of the

SCHOOL OF NATURAL RESOURCES

In Partial Fulfillment of the Requirements For the Degree of

DOCTOR OF PHILOSOPHY WITH A MAJOR IN WILDLIFE AND FISHERIES SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

2 0 0 6 2

THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE

As members of the Dissertation Committee, we certify that we have read the dissertation

prepared by Osvel Hinojosa-Huerta

entitled Birds, water, and saltcedar: strategies for riparian restoration in the Colorado River delta

and recommend that it be accepted as fulfilling the dissertation requirement for the

Degree of Doctor of Philosophy

______Date: April 7, 2006 Dr. William W. Shaw

______Date: April 7, 2006 Dr. William Mannan

______Date: April 7, 2006 Dr. Courtney Conway

______Date: April 7, 2006 Dr. Edward Glenn

______Date: April 7, 2006 Dr. Kevin Fitzsimmons

Final approval and acceptance of this dissertation is contingent upon the candidate’s submission of the final copies of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.

______Date: April 7, 2006 Dissertation Director: Dr. William Shaw 3

STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Request for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interest of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: Osvel Mario Hinojosa Huerta

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ACKNOWLEDGEMENTS

I thank Yamilett Carrillo-Guerrero for sharing this experience with me, Carlos Valdés-Casillas and Edward Glenn for introducing me into the Colorado River delta, and Bill Shaw for teaching and guiding me through my studies. My dissertation was greatly improved by the efforts and dedication of my Committee: Courtney Conway, Kevin Fitzsimmons, and Bill Mannan. The bright ideas from Alberto Macías help me in the analysis and interpretation of my results. Thank you very much. My special gratitude to José Juan Butrón Rodríguez, Juan Butrón Méndez, Magdalena Rodríguez, Martha Román, José Campoy, Mónica González, Onésimo González, Miriam Lara, Javier Mosqueda, and Don Jesús Mosqueda for their hospitality and continuous help. Alejandra Calvo-Fonseca, Jaqueline García-Hernández, Helena Iturribarría-Rojas, Damian Lester, Didio Martínez, Victor Ortega, Juan José Rivera-Díaz, Gerardo Sánchez- Bon, Pablo Valle, Michael Vamstad, Enrique Zamora, and José Alberto Zepeda have been very brave and generous to participate in the study and conservation of the Colorado River delta, many thanks. This work has been possible thanks to the wonderful help of Raquel Castro, Elena Chavarría, and Meredith de la Garza (Pronatura Noroeste-Sonora), Francisco Zamora (Sonoran Institute), Sacha Heath, Chris McCreedy, and Roy Churchwell (Point Reyes Bird Observatory), Robert Mesta, Carol Beardmore, and Jenny Dubberstein (Sonoran Joint Venture), and the support from CONACyT, the National Fish and Wildlife Foundation, the Wallace Research Foundation and the Division of Bird Habitat Conservation of the U.S. Fish and Wildlife Service. Several persons have provided me with inspiration and encouragement to get involved in the conservation of birds and the Colorado River delta: Richard Felger, David Krueper, Steve Hopp, Rickard Erickson, Kathy Molina, Kimball Garrett, Steve DeStephano, Jennifer Pitt, Eduardo Palacios, and Pamela Nagler. Thank you!

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DEDICATION

Para Yamilett

Para mis papás: Osvel y María Teresa

Para mis hermanas: Tania y Daniela

Para mis cuñados: Pepe y Alejandro

Para mis sobrinos: José Manuel, Alejandro y Angela

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TABLE OF CONTENTS

ABSTRACT……..……………………………….………...……………………...………7

INTRODUCTION…………..……………………..………..……………………….....…9

THE PRESENT STUDY…………………………..………..……………………….…..15

REFERENCES………………………………………………………………..…………21

APPENDIX A: HOVERING OVER THE ALTO GOLFO: STATUS AND CONSERVATION OF BIRDS FROM THE RÍO COLORADO TO THE GRAN DESIERTO………………………………...……...29

APPENDIX B: DENSITIES, SPECIES RICHNESS AND HABITAT RELATIONSHIPS OF THE AVIAN COMMUNITY IN THE COLORADO RIVER, MEXICO……………………………………………………….119

APPENDIX C: EFFECT OF VEGETATION TYPE AND SURFACE WATER ON RIPARIAN AVIAN COMMUNITIES ……………………………….....165

APPENDIX D: STRATEGIES FOR THE CONSERVATION OF BIRDS IN THE COLORADO RIVER DELTA, MEXICO ……………...………..…..222

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ABSTRACT

I evaluated the spatial and temporal patterns of the avian communities in the Colorado

River delta, Mexico, and their relationship with vegetation type and surface water. I also developed plausible conservation and restoration guidelines for riparian areas and native birds in the region. The study included monthly point counts at 30 transects (240 points) from May 2002 to July 2003, breeding counts at 175 sites (3 times per year) during 2002 and 2003, and habitat measurements at the survey points.

The most common species were Mourning Doves, Red-winged Blackbirds, and Brown- headed Cowbirds, but another 64 species were commonly found, including Verdins, Song

Sparrows, Yellow-breasted Chats and Abert’s Towhees. Surface water was the most important habitat feature related to avian richness and density regardless of vegetation type or land cover (P < 0.005). During summer, species richness was explained by variations in water and the cover of cottonwoods (r2 = 0.56, P < 0.001), and the variation

in bird densities was explained by variations in water and the cover of willows (r2 = 0.35,

P = 0.003).

When comparing native versus saltcedar dominated sites, both with the presence (wet) or

absence (dry) of surface water, the diversity of birds was more influenced by the presence

of water than by vegetation type. Bird abundance was more influenced by vegetation

type, but water also had an important effect, as wet sites had higher bird abundance than

dry sites with the same vegetation type, and saltcedar wet areas had similar avian abundance to native dry sites. On all cases, the presence of water was an important factor

8 determining the ecological value, in terms of avian richness, abundance, and diversity, of both native riparian and saltcedar areas. Saltcedar areas with surface water had avian characteristics similar to native riparian sites.

The dedication of instream flows and pulse floods, the maintenance of vegetation cover and structural diversity, and an increase of older riparian stands will secure the viability of existing bird populations and will increase the probability of recovery of the species that are still extirpated from the floodplain of the Colorado River in Mexico.

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INTRODUCTION

The recovery of ecosystem functions in riparian areas has become one of the major conservation goals throughout North America (Rich et al. 2003). In western North

America, about 95% of riparian areas have been destroyed, altered, or degraded by human activities (Ohmart 1994). Yet, these riparian ecosystems maintain the highest numbers of bird species and densities in the region (Knopf et al. 1988, Rosenberg et al.

1991), providing critical breeding grounds, wintering and stopover areas and migratory corridors (Ohmart and Anderson 1986, Knopf and Samson 1994, Skagen et al. 2005).

Thus, the resulting cumulative effect of habitat loss in riparian areas through the life cycle of birds has become one of the most important causes for land bird population declines in western North America (DeSante and George 1994, Hutto 2000, Norris et al.

2004).

At least 30 riparian dependant bird species have experienced these declines over the last

50 years. Declining species include not only riparian specialists, like Willow Flycatcher

(Empidonax traillii) and Yellow-billed Cuckoo (Coccyzus americanus), but also some generalists, like Song Sparrow (Melospiza melodia) and Gila Woodpecker (Melanerpes uropygialis; DeSante and George 1994, Ballard et al. 2003). The increasing dominance of saltcedar (Tamarix ramosissima), an exotic and invasive plant, has also been postulated as a cause for avian population declines in riparian areas (Anderson et al.

1977, Rosenberg et al. 1991, Ellis 1995).

Multiple efforts have been triggered to understand the biotic responses of riparian ecosystems to regeneration events. Results of these studies emphasize the importance of

10 maintaining a natural pulse flood regime, the dynamic geomorphologic processes in the floodplains, and a diverse mosaic of habitat structures (Gore 1985, Richter and Richter

2000, Stromberg and Chew 2002, Glenn et al. 2001).

The response of avian diversity and abundance to restoration efforts has been documented, showing a positive relationship with an increase of cottonwood (Populus fremontii) and willow (Salix gooddingii) cover and an increase in the structural complexity of vegetation (Scott et al. 2003, Krueper et al. 2003, Anderson et al. 2004).

However, the success of revegetation (planting) efforts in restoring riparian ecosystem functions and the native avifauna has been limited. Revegetated sites were found to have lower avian diversity, densities, and reproductive success than sites under natural regeneration processes, as a result of lower habitat diversity, structure, and unnatural patterns of hydrology (Larison et al. 2001, Snell-Rood and Cristol 2003).

Other scientists have suggested that more natural revegetation can be stimulated by releasing water from upstream reservoirs in short pulses (Richter and Richter 2000, Sher et al. 2000, Stromberg and Chew 2002, Glenn and Nagler 2005).

While revegetation has been documented as a result of pulse releases, questions remain concerning whether a highly degraded floodplain can be enhanced with a designed pulse- flood regime, and whether and how the avian community responds to such regeneration events, especially considering the dominance of saltcedar over vast areas.

Saltcedar dominated areas in riparian systems have been found to have lower bird species richness and densities than cottonwood-willow dominated sites (Anderson et al. 1977,

11

Cohan et al. 1978); and some guilds occur only in native riparian forests (Hunter et al.

1988, Rosenberg et al. 1991, Ellis 1995). However, relatively high bird richness and densities have been observed in some saltcedar areas, comparable to native riparian sites

(Brown and Johnson 1987, Hunter et al. 1988, Ellis 1995, Fleishman et al. 2003), and some endangered or sensitive species have been nesting in saltcedar dominated areas, including the Southwestern Willow Flycatcher (E. t. extimus), Yellow-billed Cuckoo, and

Yellow Warbler (Dendroica petechia; Hunter et al. 1988, Rosenberg et al. 1991, Sogge et al. 1997). Furthermore, species richness has been found to be best explained by vegetation volume, and the dominance of saltcedar was found to have no effect on species richness, abundance or evenness of birds (Fleishman et al. 2003).

In general, the ecological value of saltcedar for birds depends at least on the geographic region, vegetation biomass and habitat structure of a site (Hunter et al. 1988, Fleishman et al. 2003, Shafroth et al. 2005), as well as on the feeding behavior, nesting requirements and seasonal status of the bird species in a particular region (Rosenberg et al. 1991, Ellis

1995, Shafroth et al. 2005).

The role of instream flows or presence of surface water has not been evaluated as a potential factor in determining the relative ecological value of saltcedar compared to native riparian trees. Surface water might have a strong confounding effect in studies that compare habitat value for birds of saltcedar and native vegetation, as saltcedar tends to dominate in areas exposed to extended desiccation, while native vegetation tends to dominate in areas exposed to periodic pulse flood events, near surface water or shallow

12 groundwater (Vandersande et al. 2001, Stromberg and Chew 2002, Glenn and Nagler

2005).

There are two current approaches for the management of saltcedar and restoration of riparian systems in Western North America. One approach proposes the large-scale eradication of saltcedar whenever and wherever possible via chemical or mechanical means, in order to improve habitat quality for wildlife, salvage water, reduce fire risk, and increase recreational value (Barrows 1998, Saltcedar Task Force 2004, Hart et al.

2005). An alternative approach proposes the restoration of the natural flood regimes and the maintenance of a sustainable mix of saltcedar and native trees, which in conjunction could maintain the ecological functions and biodiversity of the original riparian systems

(Anderson 1998, Sher et al. 2000, Stromberg and Chew 2002, Glenn and Nagler 2005,

Nagler et al. 2005).

The floodplain of the Colorado River in Mexico is a major degraded environment. Before the development of the hydraulic infrastructure in the basin, the Colorado River delta supported over 200 000 hectares of riparian and wetland areas (Sykes 1937). After the completion of the larger dams in the basin in the 1930s, no base or pulse flow reached the area for nearly 50 years, causing the virtual disappearance of the cottonwood and willow forest and the invasion of saltcedar (Glenn et al. 2001). This caused the local extirpation of nine breeding species, including Southwestern Willow Flycatcher, Yellow Warbler, and Bell’s Vireo (Vireo bellii; Hinojosa-Huerta et al. 2004).

However, a modest but significant portion of the riparian ecosystem in the floodplain of the Colorado River in Mexico has been regenerated in response to large-volume water

13 releases from U.S. dams over the past 25 years (Glenn et al. 2001, Zamora-Arroyo et al.

2005). The releases have simulated a natural pulse-flood regime and a base flow, thus maintaining young and dynamic stands of cottonwood and willows, which have covered over 3000 ha despite the dominant presence of saltcedar (Nagler et al. 2005).

The interest in restoring the Colorado River delta has been increasing on both sides of the border (Valdés-Casillas et al. 1998, Pitt 2001). Opportunities for restoration have been identified (Briggs and Cornelius 1998, Luecke et al. 1999, Glenn et al. 2001) and these ideas have been discussed in public forums incorporating environmental considerations into the political, social, and economic framework (Varady et al. 2001).

This process has resulted in a binational consensus among stakeholders, agencies, environmental groups, and academia on the importance of developing and implementing a binational conservation/restoration program, based on scientific information, which would consider water requirements for wildlife conservation.

The specific objectives of my study were: 1) determine the spatial and temporal patterns of species richness, abundance, and community structure in the degraded floodplain of the Colorado River in Mexico, that was subject to regeneration through pulse-floods; 2) explore the relationships of avian richness, density and community composition with land cover and vegetation features; 3) evaluate the bird habitat values of saltcedar, considering vegetation density, habitat structural diversity, and the presence of surface water; and 4) identify plausible conservation and restoration guidelines for riparian ecosystems and native birds in the Colorado River delta.

14

These research objectives resulted in four manuscripts, included as appendices in this dissertation, each one prepared as an independent research paper to be published in a scientific journal. The manuscript in Appendix A includes the description of the avifauna of the Colorado River delta and Upper Gulf of California. The manuscript was prepared as a chapter for the book “Dry Borderlands: Great Natural Areas of the Gran Desierto and

Upper Gulf of California” (R. Felger and B. Broyles, eds.), to be published in 2006 by the

University of Utah Press.

The rest of the manuscripts have not been submitted for publication, and were prepared using the guidelines of the journal The Condor. The manuscript in Appendix B describes the spatial and temporal patterns of species richness, abundance, and community structure in the floodplain of the Colorado River in Mexico, and their relationship with habitat features. The manuscript in Appendix C presents the evaluation of the effect of vegetation type and the presence of surface water on the avian communities in the floodplain of the Colorado River in Mexico, particularly assessing the effect of the presence of saltcedar on birds when considering the presence of surface water. Finally, the manuscript on Appendix D includes the description of strategies for the conservation of birds in the Colorado River delta.

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THE PRESENT STUDY

The methods, results, and conclusions of this study are presented in the manuscripts appended to this dissertation. Following is a summary of the most important findings in this study.

STATUS AND CONSERVATION OF BIRD IN THE COLORADO RIVER DELTA

The Colorado River delta covers 169,000 ha and supports an array of contrasting

ecozones, ranging from the harsh desert to the productive wetlands. Between 1993 and

2003, 358 bird species have been detected in the Colorado delta.

Thirteen resident or breeding species of birds in this region have a status of legal protection under Mexican laws (endangered, threatened, or special protection), as well as seventeen others that use this area as stopover or wintering ground. Major causes for declines in bird populations include habitat loss and fragmentation associated with water management practices, agricultural expansion, and tourism development, as well as the introduction of exotic species of plants and animals.

Among the birds, most affected have been the riparian dependant species of the Colorado

River delta. Populations have declined regionally and four species have been extirpated locally.

Despite the changes in avian habitats, many species still thrive in the region. The delta provides habitat for migratory and wintering waterbirds and for neotropical migrant landbirds (García-Hernández et al. 2001, Mellink and Ferreira-Bartrina 2000). Nearly

16

200,000 shorebirds and 60,000 ducks and geese use the delta wetlands as wintering grounds or for stopover habitat during migration (Morrison et al. 1992, Mellink et al.

1997), and at least 110 species of neotropical migratory landbirds visit the delta during their migratory movements (Patten et al. 2001). These wetlands also provide habitat for species of international concern, such as Yuma Clapper Rail (Rallus longirostris yumanensis), California Black Rail (Laterallus jamaicensis coturniculus), Snowy Plover

(Charadrius alexandrinus), Yellow-billed Cuckoo, and Willow Flycatcher.

A trans-boundary regional plan for water management and allocation of instream flows should be developed to maintain all remnant patches of riparian vegetation and wetlands.

International guidelines need to be developed in both countries to secure that such environmental flows would remain in the river, and secure the protection of existing important sites. Binational cooperation, local participation, and a strong monitoring program under a robust scientific scheme are the keys to implement long-term conservation strategies to perpetuate the avifauna of the region.

PATTERNS OF THE AVIAN COMMUNITY IN THE FLOODPLAIN OF THE COLORADO RIVER

I determined the spatial and temporal patterns of avian richness and density and explored their relationships with habitat features in the floodplain of the Colorado River in

Mexico, which was subject to regeneration through pulse-floods in the last 20 years. The study included monthly point counts at 30 transects (240 points) from May 2002 to July

2003.

17

The average abundance per point was 29.21 individuals (± 1.20) with an average richness of 8.58 species (± 0.16), and an average density of 47.67 birds per ha (± 7.01). The most common species were Mourning Doves (Zenaida macroura), Red-winged Blackbirds

(Agelaius phoeniceus), and Brown-headed Cowbirds (Molothrus ater), but another 64 species were commonly found, including Verdins (Auriparis flaviceps), Song Sparrows, and Abert’s Towhees (Pipilo aberti).

Surface water was the most important habitat feature related to avian richness and density regardless of vegetation type or land cover (P < 0.005). During summer, species richness was explained by variations in water and the cover of cottonwoods (r2 = 0.56, P < 0.001),

and the variation in bird densities was explained by variations in water and the cover of

willows (r2 = 0.35, P = 0.003).

The dedication of instream flows and pulse floods, the maintenance of vegetation cover

and structural diversity, and an increase of older riparian stands will secure the viability of existing bird populations and will increase the probability of recovery of the species that are still extirpated from the floodplain of the Colorado River in Mexico.

EFFECT OF VEGETATION TYPE AND SURFACE WATER ON RIPARIAN AVIAN COMMUNITIES

The restoration of riparian systems in Western North America deals with the challenge of

scarce water resources and the prevalence of the invasive saltcedar. I evaluated the effect

of vegetation type and the presence of surface water on the avian communities in the

floodplain of the Colorado River in Mexico during the summer of 2002 and 2003.

18

Avian diversity and species richness was more influenced by the presence of water than by vegetation type. Bird abundance was more influenced by vegetation type, but water also had an important effect, as wet sites had higher bird abundance than dry sites with the same vegetation type, and saltcedar wet areas had similar avian abundance to native dry sites. On all cases, the presence of water was an important factor determining the ecological value, in terms of richness, abundance, and diversity, of both native riparian and saltcedar areas. Saltcedar areas with surface water had avian characteristics similar to native riparian sites.

The avian community composition was similar among habitat types and appeared to be more influenced by differences in water conditions than by vegetation type. Only 7% of the variation in community composition among sites was explained by vegetation type and the presence of water, and pairwise comparisons between habitat types resulted in an average Morisita-Horn value of 0.93 (± 0.02)

The major factors that appear to determine the ecological value for birds in riparian areas are vegetation biomass, structural diversity, and the presence of surface water. Those three components should be the focus for the management of riparian ecosystems.

The decline of native riparian forests has not been caused simply by direct competition with saltcedar, but by major disruptions of hydrological regimes in the rivers of Western

North America, including the modification or elimination of pulse flood events, canalization of streams, lowering of groundwater levels, and the elimination or reduction of instream flows

19

In the floodplain of the Colorado River in Mexico, conservation efforts should be directed to managing stream flows to increase the areas covered with surface water and re-creating periodic pulse floods within the active floodplain.

STRATEGIES FOR THE CONSERVATION OF BIRDS IN THE COLORADO RIVER DELTA

I developed strategies for the conservation of birds in the Colorado River delta. Major

goals include protecting all bird species, recovering species at risk, maintaining common

birds, and basing all actions on collaborative, voluntary efforts. I selected seven

conservation targets, which included 56 focal species: Marshbirds, Colonial Waterbirds,

Riparian Birds, Migratory Landbirds, Migratory Waterbirds, Saltgrass Bird Community,

and Marine Zone Bird Community.

The criteria for the selection of conservation targets and focal species included their

population and habitat status, current threats, endemism, considerations to cover a wide

range of ecological requirements, and considerations to develop effective biological

indicators of the system’s health.

Analysis of the focal species revealed that: 1) availability of fresh water is the major

requirement for the recovery and conservation of birds in the delta, 2) loss of habitat

structure and size has extirpated or greatly reduced breeding populations of several bird

species, and 3) recent floods and restoration efforts have recovered part of the wetland

areas, increasing the populations of threatened or endangered species.

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The general lines of action recommended for the conservation of birds in the Colorado

River delta include: 1) collaborate with the Upper Gulf of California and Colorado River

Delta Biosphere Reserve, 2) legally protect the Colorado River floodplain, 3) develop a

Management Plan with the National Water Commission for the floodplain of the

Colorado River, 4) acquire water rights to secure flows to the wetland areas, 5) expand the community-based conservation projects, 6) implement restoration projects, 7) develop a program of environmental education, and 8) develop an outreach and communications program.

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Will. 2003. Partners in Flight North American Landbird Conservation Plan. Cornell

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26

Richter, B.D. and H.E. Richter. 2000. Prescribing flood regimes to sustain riparian

ecosystems along meandering rivers. Conservation Biology 14: 1467-1478.

Rosenberg, K.V., R.D. Ohmart, W.C. Hunter, and B.W. Anderson. 1991. Birds of the

Lower Colorado River Valley. The University of Arizona Press, Tucson.

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Fe, NM.

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grazing to avian communities in riparian forests. Conservation Biology 17: 284-296.

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231-246.

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Sogge, M.K., R.M. Marshall, S.J. Sferra, and T.J. Tibbitts. 1997. A Southwestern Willow

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28

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29

APPENDIX A

HOVERING OVER THE ALTO GOLFO:

STATUS AND CONSERVATION OF BIRDS FROM THE RÍO COLORADO TO THE

GRAN DESIERTO

Manuscript prepared as a chapter for the book:

Dry Borderlands: Great Natural Areas of the Gran Desierto and Upper Gulf of California

(R. Felger and B. Broyles, eds.). University of Utah Press, Salt Lake City.

30

THE BIRDS OF THE ALTO GOLFO

HOVERING OVER THE ALTO GOLFO: STATUS AND CONSERVATION OF

BIRDS FROM THE RÍO COLORADO TO THE GRAN DESIERTO

OSVEL HINOJOSA-HUERTA

JAQUELINE GARCÍA-HERNÁNDEZ

YAMILETT CARRILLO-GUERRERO

ENRIQUE ZAMORA-HERNÁNDEZ

31

As we paddle our way through the Ciénega de Santa Clara, the living sounds of the Green Lagoons surround us - kek’s, brreet’s, wichity’s - warbling songs that rebound in the water and escape through the cattails, from above and beyond the marsh.

Such are the songs of life of the birds at the Alto Golfo, that fly, soar, hover, and wade throughout the Colorado delta, the Colorado Desert in Baja, the

Gran Desierto in Sonora, and the Sierra del Pinacate, traversing over rivers, mountains, marshes, and the ever magnificent Gulf of California.

INTRODUCTION

The admiration for birds has a long history in the region of the Alto Golfo. Deeply embedded in the native cultures of this country, the appreciation and respect for nature extends to bird species, which often symbolize mystical and mythological attributes and after which many places are named (Alvarez de Williams 1973, Broyles et al. this volume, Kniffen 1932). For the native Cucapás along the Colorado and Hardy rivers, birds are more than co-habitants of the land, they are neighbors that share valuable understanding of the patterns of nature (Onésimo González, traditional chief of the

Cucapá Tribe, El Mayor, Baja California, personal communication, March 14, 2001).

Ever since the first European explorers reached the region, the Alto Golfo has been described as a land of fascination and contrasts, a hardy place full of natural wonders, and by several, one of the most desolate places in North America (Fradkin 1984, Leopold

1989, North 1910). The Alto Golfo is also the setting for multiple stories of ecosystem

32 decay and species at risk, contrasting with surprising recoveries and amazing ecological restoration events (Glenn et al. 1996, 2001; Hinojosa-Huerta et al. 2001a, Zengel et al.

1995, 1996).

This region is as well the home for over 350 avian species and a wintering and stopover site for thousands of migratory birds (see Checklist). The multiplicity of environmental features in the region creates a mosaic of habitat types, transitioning between deserts, riparian corridors, brackish marshes, extensive mudflats, and the sea

(Felger et al. this volume). This diverse mosaic supports a complex array of bird communities, in which often Verdins (Auriparus flaviceps) are building a nest and Short- billed Dowitchers (Limnodromus scolopaceus) probing the mud, while a Sora (Porzana carolina) is whining nearby, a mixed flock of Wood-Warblers (Parulidae) is foraging intensively, and a Magnificent Frigatebird (Fregata magnificens) is over flying the area.

Some areas support a larger number of species and individuals. Nevertheless, each of the habitat types within the Alto Golfo supports a characteristic avian community of its own, and plays a role in supporting bird life in the region. Unique environmental characteristics provide habitat for some endemic birds, such as the Yuma Clapper Rail

(Rallus longirostris yumanensis) and the Large-billed Savannah Sparrow (Passerculus sandwichensis rostratus), both of which nest in the marshes and grasses of the Colorado delta.

As most of nature in the Sonoran Desert, five seasons mold bird life in the Alto

Golfo: spring, dry summer, wet summer, fall, and winter (Dimmitt 2000). The floods of the Colorado, which historically have occurred in spring and early summer, complement

33 these seasonal patterns (Zamora-Arroyo et al. 2001). The life histories of birds intermingle and match the seasons and periods of floods to shape the temporal patterns in the region, with dramatic changes in the composition of the avifauna as the seasons progress.

In this chapter we describe some of the unique characteristics of the avifauna of the

Alto Golfo. We also present the status of bird communities in the different areas of the

Alto Golfo, including the Colorado River delta, the Pinacate Region and the Gran

Desierto, complemented with an annotated checklist of birds. Finally, we discuss some of the major concerns and opportunities for bird conservation in the region.

THE SETTING

We concentrated our attention in the northernmost area of the Upper Gulf of

California, including the Colorado River delta and surrounding deserts in both Baja

California and Sonora, the marine zone of the Upper Gulf from San Felipe, Baja

California to Puerto Peñasco, Sonora, and the Gran Desierto, Sierra del Pinacate and Río

Sonoyta.

The major habitat types in the Alto Golfo region include cottonwood (Populus fremontii) and willow (Salix gooddingii) forests in the Río Colorado, marshes in the Río

Hardy and Ciénega de Santa Clara, saltcedar stands (Tamarix ramosissima) in the confluence of the Hardy and Colorado rivers, mudflats at the mouth of the Colorado and

Isla Montague, and the marine zone and rocky islands of the Upper Gulf between Puerto

Peñasco and San Felipe. Southeast from the Colorado River delta is located the string of

34 pozos along the desert escarpment, including El Doctor wetlands, and extending along the coast to the saltflats of Bahía Adaír (Ezcurra et al. 1988, Glenn et al. 2001). These pozos are tiny vegetated islands surrounded by the open desert, saltflats, and the sea. Farther east lays the volcanic desert at El Pinacate and the dunes at the Gran Desierto, the desert riparian corridor of the Río Sonoyta with a vegetation association that includes mesquite

(Prosopis spp.), palo verde (Parkinsonia spp.), and iron wood (Olneya tesota), the sandy and rocky coastal shore between el Golfo de Santa Clara and Puerto Peñasco, and the tidal estuaries at Bahía Adair, Estero Morúa, and Estero La Pinta, dominated by salt- tolerant plants (Felger et al. this volume).

A VIEW FROM THE PAST

The Alto Golfo was one of the first regions to be visited by European explorers in

1539 and 1540, yet, it was one of the last places in North America to be fully mapped,

described, and colonized (Hornaday 1908, Lumholtz 1912, Sykes 1937). This meant little

ecological disruption for birds, and until recently this whole region was a vast wilderness,

with barely a human footprint.

The remoteness of the region also meant a scarcity of biological surveys of these

biotic communities while still in pristine conditions. Nevertheless, there were a few

excellent naturalists who were brave and curious enough to adventure into the deserts,

beaches, and swamps of the Alto Golfo region.

One of the first biologists to survey this country was Edgar A. Mearns. He conducted

extensive surveys and collected over 30,000 biological specimens from 1892 to 1895 for

35 the U.S. National Museum along the U.S. – Mexico border, while serving as surgeon of the International Boundary Survey (Mearns 1907). Mearns visited the Alto Golfo from

December 1893 to May 1894. During his travels in the region, he hired Miguel, a young

Cucapá who helped him with the collections and as a guide in the region. Mearns was impressed by the harshness of the desert, the critical value of the tinajas (natural water tanks), the heat, and the lushness of the Colorado River delta. He described the delta as a tropical tract, dominated by unusually tall cottonwoods, abundant willows, and dense grassy marshes, with distinctive biological features, and abundant avifauna.

In regards to the birds in the delta, Mearns (1907:73) noted: “The tide creeks and broad bays about our camp were swarming with waterfowl, which were nowhere else seen in so great abundance. Pelicans, cormorants, geese, ducks, cranes, herons, and small waders almost covered the shores and bays, the sky was lined with their ever changing geometrical figures, and the air resounded with their winnowing wing-strokes and clanging voices, not only during the day, but through most of the night.”

William W. Price also visited the Lower Colorado and Upper Gulf before the 1900s.

He spent nearly a month between November and December 1898 observing birds in the region (Price 1899). Price found 91 species, of which he was most impressed by the

American White Pelicans (Pelecanus erythrorhynchos), describing them as extremely abundant along the lower river and the Gulf, with hundreds of flocks “that would sometimes join in immense gatherings darkening the sky” (Price 1899:90). He noted an abundance of Sandhill Cranes (Grus canadensis), especially at Laguna Salada, and the presence of hundreds of Zone-tailed Hawks (Buteo albonotatus), hovering nearby a

36 marsh wildfire “undoubtedly to prey upon the abundant cotton rats and other rodents…”

(Price 1899:91). He found waterfowl to be common, with great numbers of Brant (Branta bernicla) at Laguna Salada and Río Hardy.

In 1905-1906, the naturalists Edward W. Nelson and his assistant, Edward A.

Goldman surveyed the Baja California side of this region for the Bureau of Biological

Survey of the U.S. Department of Agriculture (Nelson 1921). Nelson himself did not visit the Colorado River delta during this expedition, but Goldman led a boat trip to the delta during the spring of 1905, accompanied by Daniel T. MacDougal, a botanist from the

Carnegie Institution of Washington. They surveyed the Río Hardy, Sierra Cucapá, Cerro

Prieto, and the Río Nuevo, during a period in which most of the area overflowed. From the Colorado Desert, near San Felipe, Nelson listed 22 species, mainly desert birds. He also included a note of the “vast numbers of waterfowl that resort to the delta of the

Colorado” in winter (Nelson 1921:112).

William T. Hornaday reported in detail the events and observations of a scientific expedition into the Pinacate during November of 1907, in which he was joined by Daniel

T. MacDougal, Godfrey Sykes, and John M. Phillips (Hornaday 1908). The expedition traversed from Tucson to the Gulf of California, passing through the town and along the river of Sonoyta. Regarding the Río Sonoyta, Hornaday (1908:83) described it as a “little stream with the desert coming down to its northern margin…on the southern bank, the oasis began and ran riot…a perfect jungle of desert willows and other small trees.”

Hornaday noted that the bird life was greater and more interesting than they expected for the region during that time of year. He made notes on about a dozen of species, including

37

Red-tailed Hawks (Buteo jamaicensis), Bald Eagles (Haliaeetus leucocephalus), Golden

Eagles (Aquila chrysaetos), Great Horned Owls (Bubo virginianus), and Phainopeplas

(Phainopepla nitens). Noteworthy observations include an American Coot (Fulica americana) and an American Bittern (Botaurus lentiginosus) at the Río Sonoyta, waterbirds in one of the aridest regions of North America.

On December 1909, the Norwegian naturalist Carl Lumholtz went into his own explorations of the Río Sonoyta, down to the Pinacate, and into the Colorado delta region, studying both the natural and cultural landscape (Lumholtz 1912). He explored the area with a party of few Mexicans and Papagos, his guides and assistants on his journeys. Lumholtz was deeply in love with the natural landscape of this region, and noted the spring events: “..the desert is radiant with good cheer,...and the hardy, healthy looking plants and trees with their abundant flowers inspire courage. One feels in communion with nature…Could I select the place where I should like best to die, my choice would be one such as this”(Lumholtz 1912:307). Lumholtz was not a professional ornithologist, thus his notes on the bird life are very general and only pertains to the most conspicuous and common species in the region. Yet, they provide valuable information from a scarcely studied region. At Río Sonoyta, he noted the presence of American

Coots, several ducks, and a small flock of geese. In the Pinacate region, Lumholtz commonly found Northern Mockingbirds (Mimus polyglottos), thrashers, hawks, falcons, and ravens; Gambel’s Quail and doves were abundant, especially in the areas nearby the tinajas. In January 1910, Lumholtz started a journey from the Pinacate to the Colorado delta. In the passage, he visited Laguna Prieta, a salt lake with cattail (Typha

38 domingensis) marshes. There, he noted the presence of seabirds, but made no reference of the species or their numbers. Later in January he arrived to the Colorado delta, where he and his party passed through thickets of willow, mesquite, and arroweed, and among marshes covered with cattails and reeds. In the delta, Lumholtz noted the abundance of shorebirds, gulls, and especially cranes.

Adriaan J. van Rossem and Joseph Grinnell worked extensively on the birds of northwestern Mexico during the 1920s and 1930s. Their work was mostly in the fields of taxonomy, distribution of avian species, and classification and description of collected specimens; van Rossem (1945) in Sonora, and Grinnell (1928) in Baja California. Their work still provides valuable baseline information to assess changes of the avifauna in the region, as it provides historic records of breeding, wintering, and transient species and subspecies at several localities, including Río Hardy, Cerro Prieto (near Río Hardy),

Rocas Consag, El Doctor, Puerto Peñasco, Isla San Jorge, and Río Colorado.

Griffing Bancroft, the prominent ornithologist of California, visited the Colorado

River delta, Colorado Desert on Baja California, and the Upper Gulf of California several times during the 1920s and 1930s (Bancroft 1922, 1926, 1932). Even though he was in awe of “the delta jungle within the desert country” (1926:209), he noticed and documented the degradation that was starting in this region. He noted: “In Mexico perhaps one half the present farming acreage was until recently, willow associations of the Delta. Salvaged, the jungle became an integral, indistinguishable portion of the major system, but the subjugation, the clearing, draining, leveling of swamps and thickets and tributaries, is one of the West’s famous achievements. A river harnessed to obey, cement

39 dams and waterworks with foundations resting on silt, lakes and canals coming or going at the word of command, an effective though unruly Slave of the Lamp” (Bancroft

1932:384-385).

During a winter hunting expedition, Bancroft (1922) observed 30 species. Most significant were the presence of Fulvous Whistling Ducks (Dendrocygna bicolor) and

Roseate Spoonbills (Ajaia ajaja), both of which are now extirpated from the delta. Ten years later, Bancroft approached the delta on board the Least Petrel, a small vessel. On his way he visited Rocas Consag, “a setting that approaches artistic perfection” (Bancroft

1932:373). At Consag, he documented the nesting of the Brown Booby (Sula leucogaster), Black Storm-petrel (Oceanodroma melania), Least Storm-petrel (O. microsoma), Peregrine Falcon (Falco peregrinus), Craveri’s Murrelet (Synthliboramphus craveri), and Red-billed Tropicbird (Phaethon aethereus). In the delta, Bancroft stopped at Montague and Gore Islands, waiting for el burro, the tidal bore (see Nelson this volume). At Montague, he discovered the nests of Large-billed Savannah Sparrows. He also looked for nests of Yuma Clapper Rails, but never found one. Bancroft was looking for nests in the right place for a characteristic clapper rail, but the local subspecies is not typical in its habitat selection, as Yuma Clapper Rails prefer freshwater or brackish inland ciénegas rather than intertidal marshes.

During his expeditions, Bancroft recognized the importance of water in maintaining the delta ecosystem, and noted that the different water sources that were dominant in some places or mixed in others resulted “in a multitude of local areas of diversified vegetation,” thus supporting a rich avifauna (Bancroft 1926:209). He was very detailed

40 describing the uniqueness of the delta, its regional importance, and the delicate balance that it supports in a border region: “Such is the delta, as fascinating, as puzzling, and as changeable as weather. Surrounded by desert and constantly fighting to preserve its identity, it is as unlike its immediate surroundings as adjoining countries well can be.

Host to most of the desert birds, which seek out its arid phases as they find them here and there, still it has, from Caracaras on the north to Large-billed Sparrows on the south, its quota of birds which hereabouts do not make their homes elsewhere” (Bancroft

1926:210).

Aldo Leopold visited the region on a hunting trip during the 1920s (Leopold 1953,

1989). After disregarding several recommendations by locals to quit the expedition due the perilous wilderness of the region, he and his brother Carl headed for Riíto, Sonora

(close to today's Ciénega de Santa Clara; Leopold mentioned it as “Rillito”). They camped in this "weird and impressive" (Leopold 1953:16) wetland system of the eastern

Colorado delta for 10 days, where they traveled following quail, geese, deer, and el tigre, the jaguar. On October 26, 1922, the Leopold brothers unloaded at the bank of a "pretty little slough" (Leopold 1953:12), where an abundance of shorebirds, cranes, spoonbills, kingfishers, ducks, cormorants, and quail welcomed them, while geese over flew on high, and the egrets on the willows "looked like a premature snow storm" (Leopold 1989:142).

He described how "dawn on the Delta was whistled in by Gambel’s Quail...and when the sun peeped, it slanted across a hundred miles of lovely desolation, a vast flat bowl of wilderness rimmed by jagged peaks” (Leopold 1989:141).

At the point of the Mesa Arenosa, near the present day Ejido Luis Encinas Johnson,

41

Leopold (1953:16) found the "green lagoons" which he described as " a series of pools, full of herons and lined with waving willows of the most delicate green; the water, bearing the reflections of the willows, is of a brilliant verdigris hue."

Further exploration led the Leopold brothers to one of the historic channels of the river, in which "a verdant wall of mesquite and willow separated the channel from the thorny desert beyond. At each bend we saw egrets, each white statue matched by its white reflection. Fleets of cormorants drove their black prows in quest of skittering mullets; avocets, willets, and yellowlegs dozed one legged on the bars, mallards, widgeons, and teals sprang skyward in alarm" (Leopold 1989:142).

Years later, Leopold (1989:144) recalled his expedition through the Colorado delta with nostalgia and sadness for a place that "has been made safe for cows and forever dull for adventurous hunters...as freedom for fear has arrived, but a glory has departed from the green lagoons."

Some of the species observed by Leopold have been extirpated from the delta, and most of the populations from the remnant species have declined. Yet, dawn in the delta is still whistled in by quail, and the sun slants across miles of lovely desolation, flat wilderness, and jagged peaks. Hope still flies around the blue skies and resounds in the marshes of the delta. With our actions and decisions we can still preserve the green lagoons for the enjoyment of the adventurous explorer within ourselves.

42

CHANGES IN AVIAN HABITATS AND COMMUNITIES

A century of human intervention has jeopardized the diversity of bird life and the ecological functions in the Alto Golfo. Thirteen resident or breeding species of birds in this region have a status of legal protection under Mexican laws (endangered, threatened, or special protection), as well as seventeen others that use this area as stopover or wintering ground (Diario Oficial de la Federación 2002; see Checklist). Major causes for declines in bird populations include habitat loss and fragmentation associated with water management practices, agricultural expansion, and tourism development, as well as the introduction of exotic species of plants and animals.

Tourism and urban development are threatening the fragile desert estuaries in the

Puerto Peñasco region, and the introduction of exotic species of plants (especially saltcedar, Felger et al. this volume) and animals (mainly rats and feral cats) is a major conservation concern over the whole region, and more critical at islands such as San

Jorge (Velarde & Anderson 1994). A program for the eradication of exotic animals has been implemented in the islands of the Gulf of California with encouraging results

(Donlan et al. 2000). Hopefully the program will eliminate this threat and help preserve the breeding colonies of seabirds on the islands.

More than 80% of the natural areas in the Colorado River delta have disappeared as a result of water management practices in the watershed and agricultural expansion in the

Mexicali Valley (Valdés-Casillas et al. 1998). Flows of the Colorado into the delta and

Upper Gulf have become irregular and scarce, and have changed the characteristics of the delta, from a brackish estuary to one with higher salinity than the sea (Glenn et al. 2001).

43

Groundwater in the San Luis and Mexicali valleys has been overexploited, lowering the water table, and negatively impacting the pozos and springs at the edge of the desert escarpment.

Among the birds, most affected have been the riparian (cottonwood-willow) dependant species of the Colorado River delta. Populations have declined regionally and four species have been extirpated locally.

Historically, the cottonwood-willow association was very common in the region, along the myriad of streams traversing the valley. This habitat type extended from the main channel in Yuma, west to the Río Nuevo, south to Cerro Prieto and Río Hardy, and east again to the Green Lagoons, at the present day Ciénega de Santa Clara and El Doctor wetlands (Felger 2000, Sykes 1937). Historic extension of the cottonwood-willow association is hard to estimate, but probably was in the tens of thousands of hectares.

Most of these hectares have been converted into agriculture, dry salt flats, or lands dominated by the exotic-invasive saltcedar. Currently, only about 1,100 hectares of cottonwood-willow remains in the delta, and is one of the largest of its kind in the whole

Lower Colorado Basin (Zamora-Arroyo et al. 2001).Some of the riparian dependant species of major concern include the Southwestern Willow Flycatcher (Empidonax traillii extimus), the Western Yellow-billed Cuckoo (Coccyzus americanus occidentalis), and the

Fulvous Whistling-Duck (Dendrocygna bicolor). These species formerly nested in the delta, but there are no recent records of breeding activity for any of them.

The Southwestern Willow Flycatcher is an endangered subspecies, whose populations have declined across the southwestern U.S. and have been extirpated from

44 northwestern Mexico (Unitt 1987). Current total population is estimated at 600 pairs

(Sogge et al. 1997). Historic nesting records of Southwestern Willow Flycatchers in the delta include Cerro Prieto and the mainstem of the river near Yuma (Sferra et al. 1997,

Unitt 1987), but no breeding has been observed recently in the delta region. However, the remnant riparian patches in the delta are an important part of the spring migration route of this species. In particular, Willow Flycatchers occupy backwater lagoons dominated by dense stands of native broadleaf trees as stopover sites on their way north (García-

Hernández et al. 2001).

Populations of Western Yellow-billed Cuckoo have also declined throughout western

North America (Hughes 1999). In the U.S., the Yellow-billed Cuckoo is protected by the state Endangered Species Act in California, and is considered a threatened species in

Arizona and Utah. Currently, the Western Yellow-billed Cuckoo is candidate for protection under the Endangered Species Act (U.S. Fish and Wildlife Service 2001).

Historically this species was a common breeder in the riparian areas of the Río Colorado

(Patten et al. 2001), with records near Cerro Prieto (Grinnell 1928). The species has been almost extirpated from much of the Lower Colorado (Rosenberg et al. 1991). Few individuals have been detected during the breeding season along the mainstem of the

Colorado in areas dominated by cottonwoods (Patten et al. 2001, see Checklist). No breeding has been confirmed yet; however some pairs might be nesting in the regenerated riparian areas of the delta.

The Fulvous Whistling Duck used to be a common breeding resident in the delta prior to the 1930s (Bancroft 1922, van Rossem 1945), but no recent records have been

45 reported (Patten et al. 2001). Other waterbirds extirpated from the Upper Gulf of

California region include Roseate Spoonbills and Sandhill Cranes. Both species were common winter visitors during the early 1900s (Bancroft 1922, Grinnell 1926, 1928,

Murphy 1917), but have not been documented in the region recently.

The populations of the Large-billed Savannah Sparrow, an endemic subspecies that winters along the coast of southern California, have also been reduced in these last decades (Unitt 1984). These sparrows nest in the saltgrass (Distichlis palmerii and D. spicata) areas of the delta. Their breeding grounds are now confined to a few places in the Ciénega de Santa Clara, El Doctor, Isla Montague, Cerro Prieto, and the mouth of the

Río Colorado (Mellink and Ferreira-Bartrina 2000, Molina and Garrett 2001).

The historic abundance of waterfowl in the Colorado delta region has become a matter of nostalgia and story-telling for local residents and hunters. Hundreds of thousands of ducks and geese from at least 26 species used to visit the region in winter

(Kramer and Migoya 1989). Habitat for wintering waterfowl has been reduced to a minimum of a few thousand hectares during the dry years in the delta. Currently, waterfowl habitat at the Ciénega de Santa Clara and Río Hardy extends over 8,000 ha.

Estero Morúa, Estero Las Pintas, and Bahía Adair near Puerto Peñasco, are also important stopover sites. Recent estimates from aerial winter surveys are of about 50,000 individuals during wet years (1993-1994) and just over 4,000 individuals during dry years (1995-1996) (U.S. Fish and Wildlife Service 1993 to 1996).

Despite the changes in avian habitats, many species still thrive in the region.

Thousands of individuals of over a hundred species of Neotropical migratory songbirds

46 stop at the revived cottonwood-willow areas of the Río Colorado, in the mesquite thickets of the Río Sonoyta, and on the strings of pozos during spring migration (mid-March to mid-June). These islands of trees surrounded by the open desert and the sea form a migratory route for birds in their journey between the wintering grounds in southern

Mexico and Central America and their breeding grounds in the U.S. and Canada. The quality of stopover sites is key in defining the population trends of migratory songbirds

(Hutto 2000, Petit 2000). Thus the conservation of stopover sites in the Alto Golfo is a critical piece in the strategies to perpetuate the populations of Neotropical migratory songbirds.

The Alto Golfo also provides critical stopover sites for migratory shorebirds, especially at Bahía Adair, the mouth of the Río Colorado, and the Ciénega de Santa

Clara. Over 150,000 shorebirds from 32 species visit the delta every year (Mellink et al.

1997, Morrison et al. 1992). For this reason, the delta is part of the Western Hemisphere

Shorebird Reserves Network (1993) and also a Wetland of International Importance in the Ramsar Convention (1998).

Marshbirds are also an important component of the avifauna of the region, especially at the Ciénega de Santa Clara, El Doctor, and Río Hardy. Six species in the rail family occur in these areas, five of which breed regularly in the region. The Yuma Clapper Rail, an endemic subspecies of the lower Colorado and delta, Endangered in the U.S. and threatened in Mexico, is locally abundant. Over 3,000 pairs breed in the Ciénega de Santa

Clara, probably more than 70% of the total population of the subspecies (Hinojosa-

Huerta et al. 2001a). Clapper Rails have benefited from accidental management practices

47 of agricultural drainage water, which has restored cattail marshes in the Ciénega and Río

Hardy. Nevertheless, these practices are not standard, and this water has not been officially allocated for the environment and could be appropriated for other uses. The habitat for the subspecies in the Ciénega is maintained with agricultural runoff from the

Welton-Mohawk Valley in Arizona. This same water is programmed to be desalted in

Yuma and sold for human consumption. If this occurs, the marsh at the Ciénega would be reduced drastically and would cause a very sharp decline in the population of Yuma

Clapper Rails.

California Black Rails (Laterallus jamaicensis coturniculus) also breed in this region

(Hinojosa-Huerta et al. 2001b). Probably there are less than 50 nesting pairs between El

Doctor and the Ciénega de Santa Clara. Inland populations of the subspecies are very rare and have declined over the last three decades (Evens et al. 1991). In Mexico, this subspecies is listed as endangered (Diario Oficial de la Federación 2002), while in the

U.S. is listed as Threatened by the State of California and considered a Species of

Concern by the U.S. Fish and Wildlife Service (California Department of Fish and Game

1999). Black Rails were thought to be absent from this region due to massive habitat degradation (Evens et al. 1991), and although these birds were probably present in the delta region earlier in the twentieth century, their occurrence was documented until 1998

(Piest and Campoy 1999). The main problem for the conservation of the subspecies is that black rails require shallow (less than 3 cm) and stable water levels in marshes near upland vegetation (Flores & Eddleman 1995), thus available habitat is very scarce and sensitive to human activities. A local threat for the subspecies might be the presence of

48 cattle at El Doctor and the Ciénega de Santa Clara, although the impact of cattle on the black rails has not been evaluated.

Neither Leopold, Nelson, Lumholtz, Price, nor Bancroft saw Rock Doves (Columba livia), House Sparrows (Passer domesticus), Ring-necked Pheasants (Phasianus colchicus), or European Starlings (Sturnus vulgaris) in the Alto Golfo region, yet these species are the most common sight today in the rural towns and around agricultural areas.

The colonization of the region by these exotic species is directly related to habitat modifications induced by human activities, but the impact on the native avifauna has not being studied in detail. These exotic species are not common in the areas where the native vegetation has been regenerated or that maintain natural habitat features, thus the impact of exotic species on populations of native birds is probably still limited.

Some native species have expanded their range and increased their populations in western North America in relation to increased human activities. Most notorious have been Red-winged Blackbirds (Agelaius phoeniceus) and Brown-headed Cowbirds

(Molothrus ater). The effect of the expansion of these species has not been evaluated in the Alto Golfo. However, the impacts of cowbirds have been carefully evaluated in other riparian areas of the Sonoran Desert, showing that habitat fragmentation and intensified farming practices have increased the nest parasitism success of cowbirds, causing population declines in riparian-dependant songbirds, such as Willow Flycatchers and

Bell’s Vireos (Vireo bellii; Powell & Steidl 2000, Sogge et al. 1997).

49

BIRD CONSERVATION IN THE ALTO GOLFO

Information on the status and population trends of avian species in the Alto Golfo is

scarce. Thus, management decisions for the conservation of birds and their habitats have

lacked the support of scientific data. Nevertheless, government agencies and

environmental organizations have achieved important conservation steps by protecting

critical areas based on requirements for focal species, such as the Yuma Clapper Rail

(Hinojosa-Huerta et al. 2001a).

In 1993, the Mexican government established the Upper Gulf of California and

Colorado River Delta Biosphere Reserve, setting the Ciénega de Santa Clara, El Doctor

wetlands, Montague Island, and the mudflats in the Río Colorado mouth as its Core Zone

(SEMARNAP 1995). This Reserve now protects more than 70% of the breeding

population of Yuma Clapper Rails and the largest breeding population of California

Black Rails in Mexico. The Reserve also protects an important breeding ground for

waterbirds at Isla Montague and habitat for over 150,000 wintering shorebirds at the river

mudflats, as well as El Doctor wetlands, one of the most important stopover sites for

Neotropical migratory passerines along western North America. The Pinacate and Gran

Desierto Biosphere Reserve was established a year later, protecting critical stopover sites

for migrant birds along desert riparian tracts of the Río Sonoyta, especially for warblers,

hummingbirds, and raptors.

Even though these two reserves encompass a combined area of 1,649,313 hectares,

important sites for birds are still without any legal protection or conservation status. One

of the most critical but unprotected bird sanctuaries is the riparian corridor of the Río

50

Colorado in Sonora and Baja California, which provide habitat for migrant and resident songbirds. Also without protection are the adjacent wetlands of the Río Hardy. These wetlands represent one of the best opportunities for restoration in the Lower Colorado

Basin (Briggs and Cornelius 1998), and are one of the strongholds for wintering waterfowl in the region. Other important unprotected sites include Estero Morúa, Estero

La Pinta, and the extended floodplain of the Río Sonoyta, lying just outside the limits of the two Biosphere Reserves. The region conformed by these sites is also a stepping stone in the migratory corridor of shorebirds, waterfowl, raptors, and over 100 species of passerines, as well as feeding ground for gulls, terns, and other seabirds.

All these unprotected areas are under strong pressures: upstream water diversions, invasion of exotic species, flood control activities, vegetation clearings, tourism and urban development, and wildfires. To overcome these threats, a binational partnership of environmental organizations, universities, and local communities are working together to cover these conservation gaps. For the Colorado River delta, a common goal is to identify sources of water that can maintain and enhance existing riparian patches in the long term.

In the mean time, a binational team in partnership with local communities is leasing marginal agricultural land near the Río Hardy to restore marsh and mesquite bosque habitat types.

Still, there are many conservation needs to be addressed in the region. In the larger picture, it is imperative for decision makers and the general public to understand that habitat degradation and population declines in birds are the result of land and water management policies that were implemented on both sides of the border without

51 accounting for the environmental consequences. The Letter of Intent signed by the U.S. and Mexican Governments for the cooperation on Sister Reserves along the border and the Joint Declaration for the enhancement of wetlands of the Colorado River delta

(Minute 306 to the US/Mexico International Water Treaty of 1944) are only the first steps for binational management of these shared ecosystems. Yet, a stronger binational dialogue should be established in order to fully protect the Alto Golfo region.

A trans-boundary regional plan for water management and allocation of instream flows should be developed to maintain all remnant patches of riparian vegetation and wetlands. International guidelines need to be developed by authorities and communities in both countries to secure that such environmental flows would remain in the river, and secure the protection of existing important sites. It is also critical to identify and implement non-governmental strategies to protect habitat for birds, especially in private and ejido lands, and in federal areas that could be used as a government lease and managed by local communities for environmental purposes. Binational cooperation, local participation, and a strong monitoring program under a robust scientific scheme are the keys to implement long-term conservation strategies to perpetuate the amazing avifauna of the Alto Golfo.

The admiration for birds has a long history in the region of the Alto Golfo. And so we continue with the tradition, enjoying the company of our feathered friends along the running waters of the Río Colorado, under bright blue skies and brilliant green willows, hoping that the current setting can be enhanced and maintained forever.

52

ACKNOWLEDGEMENTS

We thank Carlos Valdés-Casillas and Edward Glenn for introducing us into the Alto

Golfo. Our special gratitude to José Juan Butrón, Juan Butrón, Mauricio Butrón, José

Campoy, Miguel Cruz, Mónica González, Onésimo González, Miriam Lara, Javier

Mosqueda, Don Jesús Mosqueda, and Martha Román for their hospitality and continuous

help. Alejandra Calvo-Fonseca, Helena Iturribarría-Rojas, Virginie Radola, Juan José

Rodríguez-Díaz, and Gerardo Sánchez-Bon have been brave and generous enough to join

the Colorado Delta Field Crew, many thanks. Our work has been possible thanks to the

wonderful help of Sacha Heath, Chris McCreedy, and Roy Churchwell (Point Reyes Bird

Observatory), Robert Mesta (Sonoran Joint Venture), Bill Shaw and Bill Mannan (School

of Renewable Natural Resources, University of Arizona), Meredith de la Garza and

Raquel Castro (Pronatura Sonora) and the National Fish and Wildlife Foundation. This

chapter was greatly improved by editorial comments from Richard Felger.

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macularius, Cyprinidontidae) in Cienega de Santa Clara, Mexico, following an

extensive marsh dry-down. The Southwestern Naturalist 41:73-78.

Zengel, S., V. Mertetsky, E. Glenn, R. Felger, & D. Ortiz. 1995. Cienega de Santa Clara,

a remnant wetland in the Rio Colorado delta (Mexico): vegetation distribution and

the effects of water flow reduction. Ecological Engineering 4:19-36.

65

CHECKLIST OF THE BIRDS IN THE ALTO GOLFO

The species accounts summarize current knowledge on the status of birds in the Alto

Golfo, mostly based on the extensive review work done by Patten et al. (2001) in Baja

California and by Russell & Monson (1998) in Sonora. We have complemented the list with new sources published afterwards and our field observations. A list of records and observers is presented only if the species is casual or accidental in the region. We only included those species from which there is at least one definite record within the Alto

Golfo. Localities are shown in Map 000 and Gazetteer.

All unaccredited records and statements about status are based on our field observations. Observers initials are: YCG – Yamilett Carrillo-Guerrero, OHH – Osvel

Hinojosa-Huerta, HIR – Helena Iturribarría-Rojas, EZH – Enrique Zamora-Hernández,

ACF – Alejandra Calvo-Fonseca, JGH – Jaqueline García-Hernández, and MAG –

Miguel Ángel Guevara. We also included names in records by Steve Ganley (S. Ganley) and Kimball Garrett (K. Garrett), available from Steve Ganley’s web site

(http://www.primenet.com/~sganley/), and records from the field notes provided by

Richard A. Erickson (RAE).

The annotated checklist follows the taxonomic nomenclature and order of the seventh edition of the Check-list of North American Birds (American Ornithologists’

Union 1998), including the changes made in the supplements to the check-list (Banks et al. 2004). Subspecies is given only if it had relevance pertaining legal status or protection in México, as defined in the Norma Oficial Mexicana NOM-059-ECOL-2001 (Diario

66

Oficial de la Federación 2002). Names in Spanish follow Escalante et al. (1996). In cases where there is a different common name used in the region, the official name is given first, followed by the local name.

Designations for abundance and temporal status of birds are based on the categories used by Patten et al. (2001) and Russell & Monson (1998). The designations for abundance are: 1) common - frequently encountered and/or in large numbers; 2) fairly common - encountered in modest numbers; 3) uncommon - present in the area, but found infrequently; 4) rare – seen only on occasion, but range lies within the Alto Golfo; 5) casual – out of usual range, but could be expected every other year; 6) accidental – away from the normal range and not normally expected.

Designations for temporal occurrence of birds in the Alto Golfo region are: 1) resident – occurs during most of the year in the region; 2) visitor – spends a few weeks to a few months in the region; 3) transient – migrant birds that spend a short time (usually a few days) in the region; 4) vagrant – birds that have wandered off their usual range, and occur sporadically in the region.

ANSERIFORMES

ANATIDAE – DUCKS, GEESE, AND SWANS

Fulvous Whistling-Duck (Dendrocygna bicolor) - Pijiji Canelo. Former breeding

resident in Río Colorado (Bancroft 1922, van Rossem 1945), but no recent records. Post-

breeding visitors from breeding grounds at Imperial Valley might occur in Río Colorado

and Mexicali Valley (Patten et al. 2001).

67

Greater White-fronted Goose (Anser albifrons) - Ganso Careto Mayor. Rare spring transient through Colorado delta and coastal areas, more regular at Ciénega de Santa

Clara. Formerly a regular and abundant winter visitor to the Colorado delta (Saunders &

Saunders 1981).

Snow Goose (Chen caerulescens) - Ganso Blanco. Fairly common winter visitor at

Ciénega de Santa Clara and adjacent agricultural fields, although formerly much more abundant (Leopold 1989, Murphy 1917, Saunders & Saunders 1981).

Ross's Goose (Chen rossi) - Ganso de Ross. Uncommon winter visitor at Ciénega de

Santa Clara.

Brant (Branta bernicla) – Branta. Uncommon spring transient in northern Gulf, Cerro

Prieto, and Río Hardy. Casual summer (K. Garrett in Patten et al. 2001) and winter visitor at Cerro Prieto (Price 1899). B. b. nigricans, the subspecies that occurs in this region, is protected as threatened in México (Diario Oficial de la Federación 2002).

Canada Goose (Branta canadensis) - Ganso Canadiense. Common winter visitor at

Ciénega de Santa Clara and adjacent agricultural fields, uncommon elsewhere. Although most Canada Geese are B. c. moffitti (Saunders & Saunders 1981), there is one record of three individuals of the endangered Aleutian Canada Goose (B. c. leucopareia) in the

Colorado delta (Russell & Monson 1998).

Wood Duck (Aix sponsa) – Pato arcoiris. Accidental vagrant, with only one recorded at the pond of the Mexicali Zoo on July 8, 2003 (RAE).

Gadwall (Anas strepera) - Pato Pinto. Fairly common winter visitor at Ciénega de Santa

Clara and Río Hardy. Fairly common transient elsewhere in the delta and along the coast.

68

Eurasian Wigeon (Anas penelope) - Pato Silbón. Casual winter visitor, with records at

Río Hardy (Ruiz-Campos & Rodríguez-Meraz 1998), Puerto Peñasco (Russell & Monson

1998), and Cerro Prieto (RAE, January 13, 2003).

American Wigeon (Anas americana) - Pato Chalcuán. Fairly common winter visitor and casual summer visitor in the Colorado delta; common transient through the coast.

Mallard (Anas platyrhynchos) - Pato de Collar. Fairly common winter visitor in the

Colorado delta and coast, most abundant at Ciénega de Santa Clara. Uncommon non- breeding visitor in summer throughout the delta. One confirmed breeding record (a recent fledgling observed) at the Limitrophe Zone of the Colorado River, on May 31, 2000

(Data from the Arizona Breeding Bird Atlas, September 2003, facilitated by Troy

Corman from the Arizona Game and Fish Department).

Blue-winged Teal (Anas discors) - Cerceta Aliazul. Regular but uncommon winter visitor and transient at Río Hardy and Ciénega de Santa Clara. Rare summer visitor at Río

Colorado and Andrade Mesa wetlands (HIR and OHH).

Cinnamon Teal (Anas cyanoptera) - Cerceta Castaña. Uncommon breeder at Río Hardy,

Río Colorado, and the Andrade Mesa wetlands (Hinojosa-Huerta et al. 2002b). Fairly common winter visitor at Ciénega de Santa Clara and common transient through the region.

Northern Shoveler (Anas clypeata) - Pato Cucharón Norteño. Common winter visitor at

Ciénega de Santa Clara and Río Hardy. Rare non-breeding summer visitor.

Northern Pintail (Anas acuta) - Pato Golondrino Norteño. Common winter visitor at

Ciénega de Santa Clara and Río Hardy. Rare non-breeding summer visitor, one record of

69

2 males and 1 female at the Andrade Mesa wetlands on July 8, 2002 (Hinojosa-Huerta et al. 2002b).

Green-Winged Teal (Anas crecca) - Cerceta Aliverde. Common winter visitor through the delta and coastal wetlands.

Canvasback (Aythya valisineria) - Pato Coacoxtle. Uncommon winter visitor through the delta and coastal wetlands. Rare summer visitor at Ciénega de Santa Clara and

Andrade Mesa wetlands (HIR).

Redhead (Aythya americana) - Pato Cabecirrojo. Common winter visitor at Ciénega de

Santa Clara and Río Hardy; common transient through the coast. Rare summer visitor, with records at Cerro Prieto (Patten et al. 2001; RAE), Río Hardy (Ruiz-Campos &

Rodríguez-Meraz 1997), and the Andrade Mesa wetlands (Hinojosa-Huerta et al. 2002b).

Breeding has not been documented.

Ring-necked Duck (Aythya collaris) - Pato Piquianillado. Rare winter visitor in drains and marshes of the Colorado delta and coastal wetlands.

Greater Scaup (Aythya marila) - Pato-Boludo Mayor. Casual winter visitor, with only 4 records: two at Cerro Prieto (Grinnell 1928), one at Río Colorado (Patten et al. 2001), and one at Puerto Peñasco (Russell & Monson 1998).

Lesser Scaup (Aythya affinis) - Pato-Boludo Menor. Fairly common winter visitor and transient in the delta and through the coast.

Harlequin Duck (Histrionicus histrionicus) - Pato Arlequín. Casual winter visitor to

Puerto Peñasco, with only 6 birds recorded (Kaufman & Witzeman 1979, Russell &

Monson 1998).

70

Surf Scoter (Melanita perspicillata) - Negreta de Marejada. Common winter visitor and spring transient in northern Gulf, uncommon near shore.

White-winged Scoter (Melanitta fusca) - Negreta Aliblanca. Rare winter visitor in northern Gulf and off Puerto Peñasco.

Long-tailed Duck (Clangula hyemalis) - Pato Colilargo. Casual spring vagrant in the northern Gulf, with one recorded at San Felipe (Huey 1927) and another at Puerto

Peñasco (Russell & Monson 1998).

Bufflehead (Bucephala albeola) - Pato Monja. Uncommon winter visitor at Ciénega de

Santa Clara and coastal wetlands.

Common Goldeneye (Bucephala clangula) - Ojodorado Común. Rare winter visitor in

Colorado delta and coastal wetlands.

Hooded Merganser (Lophodytes cucullatus) - Mergo de Caperuza. Rare winter visitor along Río Hardy.

Common Merganser (Mergus merganser) - Mergo Mayor. Rare but sometimes numerous winter visitor and spring transient at Río Hardy, Río Colorado, Cerro Prieto,

Ciénega de Santa Clara, and Puerto Peñasco.

Red-breasted Merganser (Mergus cerrator) - Mergo Copetón. Common winter visitor on northern Gulf, with greatest numbers near Puerto Peñasco (Russell & Monson 1998), uncommon in the delta. One summer record at the Río Hardy, on July 7, 2003 (RAE).

Ruddy Duck (Oxyura jamaicensis) - Pato Tepalcate. Common winter visitor along Río

Hardy and Ciénega de Santa Clara. Uncommon breeder at Río Hardy (OHH, YCG),

71

Andrade Mesa wetlands (Hinojosa-Huerta et al. 2002b), and sewage ponds of Puerto

Peñasco (Russell & Monson 1998).

GALLIFORMES

ODONTOPHORIDAE – NEW WORLD QUAIL

California Quail (Callipepla californica) - Codorniz Californiana. Fairly common

breeding resident on the Colorado Desert region of Baja California.

Gambel's Quail (Callipepla gambelii) - Codorniz Chiquiri. Common breeding resident

throughout the region. Most abundant in the Colorado delta.

GAVIIFORMES

GAVIIDAE - LOONS

Red-throated Loon (Gavia stellata) - Colimbo Gorjirrojo. Rare winter visitor and spring

transient in the Gulf and coast of Puerto Peñasco.

Pacific Loon (Gavia pacifica) - Colimbo Ártico. Common winter visitor in the Gulf; rare

in Colorado delta (Río Hardy and Cerro Prieto).

Common Loon (Gavia immer) - Colimbo Común. Common winter visitor and migrant

(spring and fall) in the Gulf. Casual visitor off Puerto Peñasco, Ciénega de Santa Clara,

El Doctor and Cerro Prieto.

Yellow-billed Loon (Gavia adamsii) - Colimbo Piquiamarillo. Casual summer vagrant,

with only one recorded at Río Hardy (Simon & Simon 1974).

72

PODICIPEDIFORMES

PODICIPEDIDAE - GREBES

Least Grebe (Tachybaptus dominicus) – Zambullidor menor. Casual summer vagrant;

one recorded in Río Hardy at Campo Flores in May 17, 1999 (OHH). Species under

special protection in México (Diario Oficial de la Federación 2002).

Pied-billed Grebe (Podilymbus podiceps) - Zambullidor Piquipinto. Fairly common breeding resident at Ciénega de Santa Clara, uncommon at Río Hardy and agricultural drains of the Mexicali Valley. Common transient and winter visitor elsewhere.

Horned Grebe (Podiceps auritas) - Zambullidor Cornudo. Rare winter visitor in the

Gulf, Ciénega de Santa Clara, and Puerto Peñasco.

Eared Grebe (Podiceps nigricollis) - Zambullidor Orejudo. Common winter visitor

throughout the region. Uncommon summer resident at Ciénega de Santa Clara and Cerro

Prieto, but breeding activity has not been documented.

Western Grebe (Aechmophorus occidentales) - Achichilique Piquiamarillo. Uncommon

winter visitor throughout the region. Formerly a common breeding resident in the

Colorado delta, with records from the 1980s (Patten et al. 2001), but there are no recent

breeding records.

Clark's Grebe (Aechmophorus clarkii) - Achichilique Piquinaranja. Uncommon winter

visitor throughout the region, although in fewer numbers than Western Grebes. Probably

was also a breeding resident in the Colorado delta (Patten et al. 2001).

73

PROCELLARIIFORMES

DIOMEDEIDAE - ALBATROSSES

Laysan Albatross (Phoebastria immutabilis) - Albatros de Laysan. Rare spring visitor to

the northern Gulf and transient through the Mexicali Valley to the Salton Sea (Newcomer

& Silber 1989; Patten et al. 2001). Protected as a threatened species in México (Diario

Oficial de la Federación 2002).

PROCELLARIDAE – SHEARWATERS AND PETRELS

Northern Fulmar (Fulmarus glacialis) - Fulmar Norteño. Casual vagrant in the coast of

Puerto Peñasco, only two individuals recorded (Russell & Lamm 1978).

Pink-footed Shearwater (Puffinus creatopus) - Pardela Patirrosada. Fairly common

summer visitor to offshore regions of the northern Gulf.

Sooty Shearwater (Puffinus griseus) - Pardela Gris. Common summer visitor offshore in

the northern Gulf.

Black-vented Shearwater (Puffinus opisthomelas) - Pardela Mexicana. Uncommon

visitor to the northern Gulf, with three records (August, September, and December) near

the coast of Puerto Peñasco (Russell & Monson 1998).

HYDROBATIDAE – STORM-PETRELS

Leach's Storm-Petrel (Oceanodroma leucorhoa) - Paiño de Leach. Rare summer visitor

to northern Gulf (Patten et al. 2001).

Black Storm-Petrel (Oceanodroma melania) - Paiño Negro. Common resident in the

Gulf, probably breeds at Rocas Consag (Bancroft 1927, Patten et al. 2001). Common

74 close to the Sonoran shore during summer, but rare during other seasons (Russell &

Monson 1998). Protected as threatened in México (Diario Oficial de la Federación 2002).

Least Storm-Petrel (Oceanodroma microsoma) – Paiño Minimo. Common resident in the Gulf. Reported breeding at Rocas Consag (Bancroft 1927) and probably still breeds there. Uncommon during spring near Puerto Peñasco (Russell & Monson 1998).

Protected as threatened in México (Diario Oficial de la Federación 2002).

PELECANIFORMES

PHAETHONTIDAE - TROPICBIRDS

Red-billed Tropicbird (Phaethon aethereus) - Rabijunco Piquirrojo. Regular breeder at

Isla San Jorge, although uncommon near shore. Rare elsewhere in the northern Gulf.

Three individuals have been detected at Rocas Consag (Bancroft 1927; Patten et al. 2001)

and one at the mouth of the Río Colorado (van Rossem & Hachisuka 1937). Former

breeder inland at Puerto Peñasco (Russell & Monson 1998).

SULIDAE – BOOBIES AND GANNETS

Masked Booby (Sula dactylatra) - Bobo Enmascarado. Rare offshore in northern Gulf.

One record near Rocas Consag (Patten et al. 2001).

Blue-footed Booby (Sula nebouxii) - Bobo Pata Azul. Fairly common perennial visitor to

the northern Gulf and mouth of Río Colorado. Most abundant in summer and fall, during

post-breeding dispersal (Patten et al. 2001).

75

Brown Booby (Sula leucogaster) - Bobo Vientre-Blanco. Fairly common perennial visitor to northern Gulf and mouth of the Colorado (Dunning 1988, Mellink et al. 1997).

Uncommon but regular near the Sonoran shore in summer (Russell & Monson 1998).

PELECANIDAE - PELICANS

American White Pelican (Pelecanus erythrorhynchos) Pelícano Blanco Americano.

Fairly common winter and spring visitor in the Colorado delta region. Uncommon

summer visitor as non-breeder. Rare elsewhere.

Brown Pelican (Pelecanus occidentales) Pelícano Café. Common perennial visitor

throughout the coast and marine areas as a non-breeder. Inland it is a regular but

uncommon summer visitor to Cerro Prieto and Río Hardy; rare during winter.

PHALACROCORACIDAE - CORMORANTS

Brandt's Cormorant (Phalacrocorax penicillatus) - Cormorán de Brandt. Breeding at

Isla San Jorge was observed for the first time in 1999 (Cervantes-Sanchez & Mellink

2001). Rare visitor elsewhere in the northern Gulf (Russell & Monson 1998).

Double-crested Cormorant (Phalacrocorax auritus) - Cormorán Bicrestado. Common perennial non-breeding visitor to the Colorado delta and coastal areas, with increased numbers between November and February.

FREGATIDAE - FRIGATEBIRDS

Magnificent Frigatebird (Fregata magnificens) Fragata Magnífica. Uncommon post-

breeding visitor (May-September) through coastal and marine areas. Rare at other

months.

76

CICONIIFORMES

ARDEIDAE – HERONS AND BITTERNS

American Bittern (Botaurus lentiginosus) - Torcomón. Uncommon breeder and winter

visitor at the Ciénega de Santa Clara; rare visitor at Río Hardy and associated drains.

Least Bittern (Ixobrychus exilis) – Garcita de Tular. Common breeding resident at the

Ciénega de Santa Clara; uncommon at Río Hardy, Río Colorado, and Andrade Mesa

wetlands (Hinojosa-Huerta et al. 2002b).

Great Blue Heron (Ardea herodias) - Garzón Cenizo. Common breeding resident at

Colorado delta and coastal wetlands of the Sonoran shore.

Great Egret (Ardea alba) - Garza Blanca. Common breeding resident at Cerro Prieto,

Río Hardy, and agricultural drains of the Mexicali Valley. Perennial non-breeding visitor

at other wetland areas.

Snowy Egret (Egretta thula) - Garza Nivea. Common local breeding resident at Isla

Montague and Cerro Prieto (Molina & Garrett 2001, Palacios & Mellink 1992). Common

visitor throughout the Colorado delta and coastal wetlands.

Little Blue Heron (Egretta caerulea) - Garceta Azul. Rare summer visitor to coastal

wetlands of Puerto Peñasco and probably the Colorado delta.

Tricolored Heron (Egretta tricolor) - Garza Tricolor. Rare summer vagrant in the

Colorado delta, more regular at the Ciénega de Santa Clara. Nesting by two pairs

observed on 2002 suggest that the species might be a rare breeder in the region (Mellink

et al. 2002).

77

Reddish Egret (Egretta rufescens) - Garza Rojiza. Casual vagrant in the Colorado delta and coastal wetlands of Baja and Sonora and probably and occasional breeder at Isla

Montague (Mellink et al. 2002). Species under special protection in México (Diario

Oficial de la Federación 2002).

Cattle Egret (Bubulcus ibis) - Garza Ganadera. Common breeding resident in the

Mexicali Valley. Colonized this region in the 1960s (Mora 1997). Uncommon breeder and transient on the coast of Sonora. Nine egrets were recorded in the Pinacate region in

1987 (Russell & Monson 1998).

Green Heron (Butorides virescens) - Garza Verde. Common breeding resident at Río

Colorado, Río Hardy, and Ciénega de Santa Clara.

Black-crowned Night Heron (Nycticorax nycticorax) - Garza-Nocturna Coroninegra.

Fairly common breeding resident throughout the Colorado delta. Uncommon visitor to the coastal wetlands of Puerto Peñasco.

THRESKIORNITHIDAE – IBISES AND SPOONBILLS

White Ibis (Eudocimus albus) - Ibis Blanco. Casual vagrant to the Colorado delta and

Sonoran coast. Seven birds were observed at the Ciénega de Santa Clara on March 11,

1999 (OHH).

White-faced Ibis (Plegadis chihi) - Ibis Cariblanco. Common winter visitor in the

Mexicali Valley and Ciénega de Santa Clara. Common transient through the Sonoran coast. Probably breeds along Río Colorado and Ciénega de Santa Clara.

78

Roseate Spoonbill (Ajaia ajaja) - Espátula Rosada. Formerly an irregular but numerous winter visitor in the Colorado delta (Bancroft 1922, Grinnell 1926). There are no records since the 1920s.

CICONIIDAE - STORKS

Wood Stork (Mycteria americana) - Cigüeña Americana. Formerly a common post-

breeding visitor, but now is a rare visitor, with few records along Río Colorado and Río

Hardy (Mellink et al. 2002, Ruiz-Campos & Rodríguez-Meraz 1997; HIR 2002, 2003).

Species under special protection in México (Diario Oficial de la Federación 2002).

CATHARTIDAE – NEW WORLD VULTURES

Black Vulture (Coragyps atratus) - Zopilote Negro. Rare visitor to Pinacate and Río

Sonoyta region.

Turkey Vulture (Cathrates aura) - Aura Cabecirroja. Common perennial inland visitor

throughout the region.

FALCONIFORMES

ACCIPITRIDAE – HAWKS, KITES, AND EAGLES

Osprey (Pandion haliaeetus) – Águila Pescadora. Uncommon breeding resident along

Río Colorado and Puerto Peñasco. Fairly common non-breeding resident throughout the

delta and coastal areas.

White-tailed Kite (Elanus leucurus) - Milano Coliblanco. Fairly common breeding resident in Río Colorado and Mexicali Valley. Started to colonize the region in the late

1970s (Rosenberg et al. 1991).

79

Bald Eagle (Heliaeetus leucocephalus) - Águila Cabeciblanca. Uncommon winter visitor, with birds regularly visiting the Ciénega de Santa Clara and Río Hardy each winter. Protected as an endangered species in México (Diario Oficial de la Federación

2002).

Northern Harrier (Circus cyaneus) - Gavilán Rastrero. Common winter visitor and transient throughout the Colorado delta and coastal wetlands. More abundant at Ciénega de Santa Clara.

Sharp-shinned Hawk (Accipiter striatus) - Gavilán Pajarero. Uncommon winter visitor and transient in the Colorado delta region. Species under special protection in México

(Diario Oficial de la Federación 2002).

Cooper's Hawk (Accipiter cooperi) - Gavilán de Cooper. Uncommon winter visitor and transient throughout the delta and Sonoran coast. Species under special protection in

México (Diario Oficial de la Federación 2002).

Harris' Hawk (Parabuteo unicinctus) - Aguililla de Harris. Casual visitor to El Doctor and Puerto Peñasco, with only two recent records (Russell & Monson 1998). It is reported as a common breeding resident before the 1930s (Grinnell 1928). Species under special protection in México (Diario Oficial de la Federación 2002).

Red-shouldered Hawk (Buteo lineatus) – Aguililla Pechirroja. Only two records, both of them juveniles, at Mexicali on January 1989 and December 1994 (Patten et al. 2001).

Species under special protection in México (Diario Oficial de la Federación 2002).

Swainson's Hawk (Buteo swainsoni) - Aguililla de Swainson. Uncommon winter visitor in the Colorado delta, sometimes observed in flocks (about 30 individuals) in agricultural

80 fields.. Rare spring transient through Puerto Peñasco and the Colorado delta. One summer record near Algodones, BC, on July 7, 2003 (RAE). Species under special protection in México (Diario Oficial de la Federación 2002).

Zone-tailed Hawk (Buteo albonotatus) – Aguililla Aura. Uncommon winter visitor.

Previously unrecorded in the region. We observed two individuals on September 24,

2002, two on November 19, 2002, and three on December 19, 2002. all along the riparian corridor of the Río Colorado.

Red-tailed Hawk (Buteo jamaicensis) - Aguililla Coliroja. Common inland winter visitor and uncommon breeder throughout the region.

Ferruginous Hawk (Buteo regalis) - Agulilla Real. Uncommon but regular winter visitor, especially around Puerto Peñasco. Rare in the Colorado delta. Species under special protection in México (Diario Oficial de la Federación 2002).

Golden Eagle (Aquila chrysaetos) - Águila Real. Casual visitor at Río Sonoyta (Sonoyta to Puerto Peñasco), with only three records (Russell & Monson 1998), and at Río

Colorado, with only one record (JGH, July 2003). Species protected as threatened in

México (Diario Oficial de la Federación 2002).

FALCONIDAE - FALCONS

Crested Caracara (Caracara plancus) - Caracara Común. Former rare winter visitor in

the Colorado delta (Grinnell 1928, Stone & Rhoads 1905). Only one record at the coast

near Puerto Peñasco, and breeding is presumed near Sonoyta (Russell & Monson 1998).

81

American Kestrel (Falco sparverius) - Cernícalo Americano. Common breeding resident in the Colorado delta. Presumed breeding near Sonoyta (Russell & Monson

1998). Common winter visitor and transient throughout the region.

Merlin (Falco columbarius) – Esmerejón. Rare winter visitor and transient in the

Colorado delta, Puerto Peñasco, and near Sonoyta.

Peregrine Falcon (Falco peregrinus) - Halcón Peregrino. Rare but regular winter visitor and transient in the Colorado delta and Puerto Peñasco. Probably breeds on Rocas

Consag (Bancroft 1927). Species under special protection in México (Diario Oficial de la

Federación 2002).

Prairie Falcon (Falco mexicanus) - Halcón Pradeño. Rare winter visitor and transient through the Colorado delta, Pinacate, Puerto Peñasco, and Río Sonoyta. Species protected as threatened in México (Diario Oficial de la Federación 2002).

GRUIFORMES

RALLIDAE – RAILS, GALLINULES, AND COOTS

California Black Rail (Laterallus jamaicensis coturniculus) – Polluela Negra, Ralito

Negro. Rare breeding resident at Ciénega de Santa Clara and El Doctor, with less than 50

pairs (Hinojosa-Huerta et al. 2001b). Subspecies listed as endangered in México (Diario

Oficial de la Federación 2002) and as a priority taxon for conservation in the U.S.

(California Department of Fish and Game 1999). Single birds detected at Laguna del

Indio (May 25, 2001), Río Hardy (May 30, 2001), Río Colorado (June 9, 2002), and a

canal at Ejido Luis Encinas Johnson (June 13, 2002).

82

Yuma Clapper Rail (Rallus longirostris yumanensis) – Rascón Picudo de Arizona,

Palmoteador de Yuma. Common breeding resident at Ciénega de Santa Clara, with an estimated population of over 6,000 individuals (Hinojosa-Huerta et al. 2001a).

Uncommon at other wetland sites, including Río Hardy, Río El Mayor, El Doctor, Río

Colorado mainstem, All-American Canal marshes and throughout agricultural drains in the Mexicali Valley. Subspecies endemic to Lower Colorado River and Delta, listed as threatened in México (Diario Oficial de la Federación 2002) and endangered in the U.S.

(Eddleman & Conway 1998).

Virginia Rail (Rallus limicola) - Rascón Limícola. Common breeding resident at

Ciénega de Santa Clara and El Doctor, with numbers augmented by winter visitors. Rare breeder at Ríos Hardy and Colorado. Rare transient in Río Sonoyta and Puerto Peñasco region. Species under special protection in México (Diario Oficial de la Federación

2002).

Sora (Porzana carolina) - Polluela Sora. Common winter visitor at Ciénega de Santa

Clara, El Doctor, and Río Hardy, where it is a rare summer visitor and probably breeds.

Uncommon transient in Río Sonoyta, Puerto Peñasco, and Río Colorado.

Common Moorhen (Gallinula chloropus) - Gallineta Común. Common breeding resident throughout marshes of the Colorado delta. Rare visitor to Puerto Peñasco and

Río Sonoyta.

American Coot (Fulica americana) - Gallareta Americana. Common breeding resident throughout marshes of the Colorado delta, with numbers augmented by winter visitors.

Common transient and winter visitor in Puerto Peñasco and Río Sonoyta.

83

GRUIDAE - CRANES

Sandhill Crane (Grus canadensis) - Grulla Canadiense. Formerly a common winter

visitor in the Colorado delta (Leopold 1989, Murphy 1917, van Rossem 1945), but no

records since the 1930s. Only two records elsewhere, at Río Sonoyta (Audubon 1906)

and Puerto Peñasco (Russell & Monson 1998).

CHARADRIIFORMES

CHARADRIIDAE - PLOVERS

Black-bellied Plover (Pluvialis squatarola) - Chorlo Gris. Common transient and winter

visitor at Ciénega de Santa Clara, El Doctor, and through the coast. Uncommon summer

visitor in the same areas.

Snowy Plover (Charadrius alexandrinus nivosus) – Chorlito Niveo. Uncommon

breeding resident at El Doctor saltflats, Ciénega de Santa Clara, and Cerro Prieto ponds.

Western populations have declined since the 1920s (Powell 1998), and is listed as

threatened in Mexico (Diario Oficial de la Federación 2002) and Endangered in the U.S.

(Powell 1998).

Wilson's Plover (Charadrius wilsonia) - Chorlito Piquigrueso. Common breeding

resident in the coastal wetlands of Puerto Peñasco. Uncommon winter visitor at Ciénega

de Santa Clara, El Doctor, and Isla Montague. Formerly bred at San Felipe (Patten et al.

2001).

84

Semipalmated Plover (Charadrius semipalmatus) - Chorlito Semipalmeado. Fairly common transient at Ciénega de Santa Clara, El Doctor, Río Colorado and along the coast. Uncommon winter visitor in the Colorado delta.

Piping Plover (Charadrius melodus) - Chorlito Chiflador. Rare winter visitor and transient in the region, with seven records near Puerto Peñasco (Russell & Monson 1998) and two at the Ciénega de Santa Clara (March 1999 and December 2004; OHH). Species listed as endangered in México (Diario Oficial de la Federación 2002).

Killdeer (Charadrius vociferus) – Chorlito Tildío. Common breeding resident in the

Colorado delta, coastal areas, and Río Sonoyta.

Mountain Plover (Charadrius montanus) - Chorlito Llanero. Regular winter visitors between Puerto Peñasco, Sonoyta, and the Pinacate region (Russell & Monson 1998).

Might also winter in the northern Mexicali Valley (Patten et al. 2001). Species protected as threatened in México (Diario Oficial de la Federación 2002).

HAEMATOPODIDAE - OYSTERCATCHERS

American Oystercatcher (Haematopus palliatus) - Ostrero Americano. Uncommon

perennial visitor to coastal areas of the northern Gulf. Breeds locally at Isla Montague

(Peresbarbosa and Mellink 2001) and coastal wetlands of the Puerto Peñasco region

(Russell & Monson 1998).

Black Oystercatcher (Haematopus bachmani) - Ostrero Negro. Casual vagrant, with

only three records from Puerto Peñasco (Russell & Monson 1998).

RECURVIROSTRIDAE – STILTS AND AVOCETS

85

Black-necked Stilt (Himantopus mexicanus) - Candelero Americano. Common breeding resident throughout the Colorado delta and Mexicali Valley.

American Avocet (Recurvirostra americana) - Avoceta Americana. Common perennial visitor throughout the Colorado delta, with greatest numbers registered at Laguna Salada,

Cerro Prieto, and Ciénega de Santa Clara. Uncommon breeder at Ciénega de Santa Clara and Cerro Prieto. Common winter visitor and transient along the coast.

SCOLOPACIDAE – SANDPIPERS AND PHALAROPES

Greater Yellowlegs (Tringa melanoleuca) - Patamarilla Mayor. Fairly common transient

and winter visitor in the Colorado delta and through the coast.

Lesser Yellowlegs (Tringa flavipes) - Patamarilla Menor. Fairly common transient in the

Colorado delta and through the coast. Uncommon winter visitor in Puerto Peñasco

(Russell & Monson 1998) and the Colorado delta (Patten et al. 1993).

Solitary Sandpiper (Tringa solitaria) - Playero Solitario. Rare fall transient and winter

visitor in Colorado delta, with only six records (Patten et al. 2001; RAE September 2000;

OHH March 2002).

Willet (Catoptrophorus semipalmatus) - Playero Pihuiui. Common transient and winter

visitor in the Colorado delta and coastal areas. Rare summer visitor in Peñasco and

Colorado delta.

Wandering Tattler (Heteroscelus incanus) - Playero Vagabundo. Uncommon winter

visitor and transient along the coast of the northern Gulf. Casual in the Colorado delta.

86

Spotted Sandpiper (Actitis macularia) - Playero Alzacolita. Fairly common transient and winter visitor in the Colorado delta and coastal areas. Rare summer visitor in the

Colorado delta.

Whimbrel (Numenius phaeopus) - Zarapito Trinador. Common winter visitor and transient in the Mexicali Valley, Colorado delta, and coastal areas. Few individuals regularly summer in alfalfa fields of the Mexicali Valley.

Long-billed Curlew (Numenius americanus) - Zarapito Picolargo. Common transient and winter visitor in the Colorado delta and coastal areas.

Marbled Godwit (Limosa fedoa) - Picopando Canelo. Common transient and winter visitor, with major aggregations at the Ciénega de Santa Clara and Puerto Peñasco.

Regular uncommon summer visitor.

Ruddy Turnstone (Arenaria interpres) - Vuelvepiedras Rojizo. Fairly common transient and winter visitor at the coastal areas of the northern Gulf. Casual at Cerro Prieto (Patten et al. 2001).

Black Turnstone (Arenaria melanocephala) - Vuelvepiedras Negro. Uncommon transient and winter visitor at the coastal areas of the northern Gulf.

Surfbird (Aprisa virgata) - Playero de Marejada. Common spring transient and uncommon winter visitor along the shore of the northern Gulf.

Red Knot (Calidris canutus) - Playero Gordo. Fairly common, but sometimes numerous, transient and winter visitor on the coast of the northern Gulf. Casual at Cerro Prieto.

Sanderling (Calidris alba) - Playero Blanco. Common transient and winter visitor along the coast, less abundant at Colorado delta.

87

Semipalmated Sandpiper (Calidris pusilla) - Playerito Semipalmeado. A rare transient along the coast of the Gulf of California. Only three records, one near San Felipe

(Wurster & Radamaker 1992), and two at Puerto Peñasco (Russell & Monson 1998).

Western Sandpiper (Calidris mauri) - Playerito Occidental. Common transient and winter visitor through the Colorado delta and coastal areas.

Least Sandpiper (Calidris minutilla) - Playerito Mínimo. Common transient and winter visitor through the Colorado delta and coastal areas, although less numerous than

Western Sandpipers.

Baird's Sandpiper (Calidris bairdii) - Playerito de Baird. Probably a rare fall transient, but only three records (Patten et al. 1993, 2001; Russell & Monson 1998).

Pectoral Sandpiper (Calidris melanotus) - Playerito Pectoral. Casual fall vagrant along the coast, only two records (Gallucci 1981, Russell & Monson 1998).

Dunlin (Calidris alpina) - Playero Dorsirojo. Fairly common transient winter visitor throughout the Colorado delta and along the coast.

Stilt Sandpiper (Calidris himantopus) - Playero Zancudo. Only two records, at Cerro

Prieto (Patten et al. 2001), and Ciénega de Santa Clara (March 22, 2003; MAG, OHH), but probably an uncommon transient.

Short-billed Dowitcher (Limnodromus griseus) - Costurero Piquicorto. Common winter visitor and spring transient, fairly common fall transient. Most numerous at Ciénega de

Santa Clara.

88

Long-billed Dowitcher (Limnodromus scolopaceus) - Costurero Piquilargo. Common transient and winter visitor at Colorado delta and along the coast. Most abundant near El

Golfo de Santa Clara.

Common Snipe (Gallinago gallinago) - Agachona Común. Uncommon transient and winter visitor at Colorado delta and coastal wetlands.

Wilson's Phalarope (Phalaropus tricolor) - Falarapo de Wilson. Common transient through the coast and Colorado delta, and can be numerous at Cerro Prieto. Casual winter visitor in the northern Gulf.

Red-necked Phalarope (Phalaropus lobatus) - Falarapo Cuellirrojo. Common transient through the coast and Colorado delta. Aggregations of about 10,000 birds were documented at Cerro Prieto (Patten et al. 2001).

Red Phalarope (Phalaropus fulicaria) - Falarapo Piquigrueso. Casual transient and winter visitor. Only three records, one at San Felipe in 1926 (Huey 1927), a group of 30 at Puerto Peñasco in 1979, and a single bird at Peñasco on 1990 (Russell & Monson

1998).

LARIDAE – JAEGERS, GULLS, TERNS, AND SKIMMERS

Pomarine Jaeger (Stercorarius pomarinus) - Salteador Pomarino. Rare winter visitor

and transient in the northern Gulf, with three records near San Felipe (Patten et al. 2001),

one in the Gulf (Wilbur 1987), and one at Puerto Peñasco (Russell & Monson 1998).

Parasitic Jaeger (Stercorarius parasiticus) - Salteador Parásito. Rare winter visitor and

transient in the northern Gulf, with one inland record at Cerro Prieto, two records near

San Felipe (Patten et al. 2001), and two at Puerto Peñasco (Russell & Monson 1998).

89

Long-tailed Jaeger (Stercorarius longicaudus) - Salteador Colilargo. Casual fall vagrant, only recorded at Cerro Prieto (Patten et al. 2001).

Laughing Gull (Larus atricilla) - Gaviota Reidora. Fairly common breeder at Isla

Montague (Palacios and Mellink 1992) and Cerro Prieto (Molina & Garrett 2001). Fairly common summer and rare winter visitor throughout the region.

Franklin's Gull (Larus pipixcan) - Gaviota de Franklin. Rare spring transient and casual summer visitor. Records in Cerro Prieto, San Felipe, Laguna Salada (Patten et al. 2001),

Golfo de Santa Clara, and Puerto Peñasco (Russell & Monson 1998).

Bonaparte's Gull (Larus philadelphia) - Gaviota de Bonaparte. Fairly common transient and winter visitor at Cerro Prieto, Río Hardy, Ciénega de Santa Clara, and the coastal areas.

Heermann's Gull (Larus heermanni) - Gaviota de Heermann. Common perennial non- breeding visitor to the northern Gulf. Species under special protection in México (Diario

Oficial de la Federación 2002).

Mew Gull (Larus canus) – Gaviota Piquiamarilla. Only one record from the 1994

Christmas Bird Count at Puerto Peñasco (S. Ganley). Patten et al. (2001) report it as a probably rare but regular winter visitor.

Ring-billed Gull (Larus delawarensis) - Gaviota Piquianillada. Common transient and winter visitor throughout the region, less numerous as a non-breeding summer visitor, especially in the Colorado delta.

California Gull (Larus californicus) - Gaviota Californiana. Common winter visitor and uncommon non-breeding summer visitor.

90

Herring Gull (Larus argentatus) - Gaviota Plateada. Fairly common winter visitor.

Sometimes numerous at Puerto Peñasco (Russell & Monson 1998).

Thayer's Gull (Larus thayeri) - Gaviota de Thayer. Rare winter visitor to the northern

Gulf, with only few records near San Felipe and Cerro Prieto (RAE).

Lesser Black-backed Gull (Larus fuscus) – Gaviota Dorsinegra Menor. Casual winter vagrant, with only one record at Puerto Peñasco during a Christmas Bird Count (National

Audubon Society 2002).

Yellow-footed Gull (Larus livens) - Gaviota Patamarilla. Common non-breeding visitor year-round in the northern Gulf and along the coast; common summer visitor and transient in the Colorado delta. Species under special protection in México (Diario

Oficial de la Federación 2002).

Western Gull (Larus occidentalis) - Gaviota Occidental. Rare but regular winter visitor in the northern Gulf, San Felipe, and Puerto Peñasco.

Glaucous-winged Gull (Larus glaucescens) - Gaviota Aliglauca. Rare winter visitor, with records from San Felipe (Huey 1927, Patten et al. 2001) and Puerto Peñasco

(Russell & Monson 1998).

Glaucous Gull (Larus hyperboreus) - Gaviota Blanca. Rare and irregular winter visitor to northern Gulf. Only six records, two from San Felipe (Patten et al. 2001) and four from

Puerto Peñasco (Russell & Monson 1998).

Sabine's Gull (Xema sabini) - Gaviota de Sabine. Casual fall transient, with only two records from Puerto Peñasco (Russell & Lamm 1978).

91

Black-legged Kittiwake (Rissa tridactyla) - Gaviota Pata Negra. Casual winter vagrant, with only one record from Puerto Peñasco (Russell & Monson 1998).

Gull-billed Tern (Sterna nilotica vanrossemi) – Gallito piquigrueso. Status of western subspecies vanrossemi uncertain, but probably in declining numbers and is under consideration to be listed as Endangered in the U.S. (Parnell et al. 1995). Common breeder at Isla Montague and Cerro Prieto ponds. Common visitors to the Colorado mainstem, Río Hardy, canals, and drains as foragers. These colonies, along with the

Salton Sea population, are the stronghold in their northern range (Molina and Garrett

2001).

Caspian Tern (Sterna caspia) - Golondrina-Marina Cáspica. Uncommon breeder at

Cerro Prieto (Mellink et al. 2002, Molina & Garrett 2001), fairly common perennial visitor throughout the Colorado delta and coastal areas.

Royal Tern (Sterna maxima) - Golondrina-Marina Real. Fairly common but irregular breeder at Isla Montague (Palacios & Mellink 1993, Peresbarbosa & Mellink 2001); fairly common perennial visitor along the coast.

Elegant Tern (Sterna elegans) - Golondrina-Marina Elegante. Irregular breeder at Isla

Montague (Peresbarbosa & Mellink 2001); fairly common non-breeding visitor along the coast. Species under special protection in México (Diario Oficial de la Federación 2002).

Common Tern (Sterna hirundo) - Golondrina-Marina Común. Common transient and rare winter visitor, especially around Puerto Peñasco (Russell & Monson 1998), but also recorded at Cerro Prieto (Patten et al. 2001).

92

Forster's Tern (Sterna forsteri) - Golondrina-Marina de Forster. Uncommon breeder at

Cerro Prieto (Molina & Garrett 2001). Common perennial visitor throughout the region.

Least Tern (Sterna antillarum) - Golondrina-Marina Mínima. Uncommon breeder, with colonies at Isla Montague, El Doctor, and coastal wetlands north of San Felipe and Puerto

Peñasco (Palacios & Mellink 1996). Uncommon spring and summer visitor at other wetland and coastal areas; casual fall transient and winter visitor along the coast (Russell

& Monson 1998). Species under special protection in México (Diario Oficial de la

Federación 2002).

Black Tern (Chlidonias niger) - Golondrina-Marina Negra. Common transient through the Colorado delta and the coast. Uncommon summer visitor at Andrade Mesa wetlands

(Hinojosa-Huerta et al. 2002).

Black Skimmer (Rhynchops niger) - Rayador Americano. Common breeder at Isla

Montague (Peresbarbosa & Mellink 1994) and Cerro Prieto (Molina & Garrett 2001).

Fairly common transient and winter visitor along the coast, especially at El Golfo de

Santa Clara and Puerto Peñasco.

ALCIDAE – AUKS, MURRES, AND PUFFINS

Craveri's Murrelet (Synthliboramphus craveri) - Mérgulo de Craveri. Reported

breeding at Rocas Consag by Bancroft (1927). Probably a resident on the northern Gulf

(Patten et al. 2001). The species is listed as threatened in México (Diario Oficial de la

Federación 2002).

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COLUMBIFORMES

COLUMBIDAE – PIGEONS AND DOVES

White-winged Dove (Zenaida asiatica) - Paloma Aliblanca. Common breeding visitor

throughout the delta, more numerous in the riparian corridor of the Colorado.

Mourning Dove (Zenaida macroura) - Paloma Huilota. Common breeding resident

throughout the region.

Inca Dove (Columbina inca) - Tórtola Colilarga. Uncommon breeding resident in the

Colorado delta, Puerto Peñasco, and Río Sonoyta.

Common Ground-Dove (Columbina passerina) - Tórtola Común. Common breeding

resident at Río Colorado and Río Sonoyta.

Ruddy Ground-Dove (Columbina talpacoti) - Tórtola Rojiza. Casual vagrant, only one

record at Puerto Peñasco (Russell & Monson 1998).

CUCULIFORMES

CUCULIDAE – CUCKOOS AND ROADRUNNERS

Yellow-billed Cuckoo (Coccyzus americanus occidentalis) - Cuco Piquiamarillo.

Western populations have declined drastically (Hughes 1999), and the subspecies has

been almost extirpated from the Colorado delta. Recent records during breeding season (1

pair in July 1995 – Patten et al. 2001; 1 bird in June 2000, 2 pairs in July 2001, 2 singing

males in June 2002, and 6 singing males in 2003 - YCG, OHH, HIR, and EZH) suggest

that cuckoos might nest in the restored riparian patches of Río Colorado. The western

94 subspecies is under consideration to be listed as Endangered in the U.S (U.S. Fish and

Wildlife Service 2001).

Greater Roadrunner (Geococcyx californianus) - Correcaminos Mayor. Fairly common breeding resident in the riparian and desertscrub areas.

STRIGIFORMES

TYTONIDAE - OWLS

Barn Owl (Tyto alba) - Lechuza de Campanario. Uncommon breeding resident

throughout the Colorado delta, Pinacate, and Puerto Peñasco.

STRIGIDAE - OWLS

Western Screech-Owl (Otus kennicottii) - Tecolote Occidental. Formerly an abundant

breeder along the Río Colorado (Russell & Monson 1998), now an uncommon breeding

resident. Rare breeding resident along Río Sonoyta/Pinacate region.

Great Horned Owl (Bubo virginianus) - Búho Cornudo. Fairly common breeding resident throughout the region.

Elf Owl (Micrathene whitneyi) - Tecolotito Enano. Probably was an uncommon breeder along Río Colorado (Wilbur 1987), but there are no recent records from the delta.

Common summer resident near Sonoyta, where breeding is presumed (Russell & Monson

1998).

Burrowing Owl (Athene cunicularia) - Búho Llanero. Common breeding resident throughout the Mexicali Valley, with an estimated population of 3,800 individuals

(Iturribarría-Rojas 2002), conforming the largest population in the Baja California

95 peninsula (Palacios et al. 2000). Less abundant in winter. Uncommon breeder around

Puerto Peñasco.

Long-eared Owl (Asio otus) - Búho Cornudo-Caricafé. Casual winter visitor around San

Felipe, Puerto Peñasco and the Pinacate region. Only four records for the region (Russell

& Monson 1998, Patten et al. 2001; RAE February 1998).

Short-eared Owl (Asio flammeus) - Búho Orejicorto. Rare winter visitor throughout the delta and Puerto Peñasco. Species under special protection in México (Diario Oficial de la Federación 2002).

Northern Saw-whet Owl (Aegolius acadicus) - Tecolote-Abetero Norteño. Only one record: a freshly killed bird near Puerto Peñasco on November 1977 (Russell & Monson

1998).

CAPRIMULGIFORMES

CAPRIMULGIDAE - NIGHTHAWKS

Lesser Nighthawk (Chordeiles acutipennis) - Chotacabras Menor, Tapacaminos.

Common breeder and rare winter visitor throughout the Colorado delta. Uncommon

breeder at Río Sonoyta, Pinacate, and Puerto Peñasco.

Common Poorwill (Phalaenoptilus nuttallii) - Pachacua Norteña. Fairly common

breeding resident along Río Colorado and Río Sonoyta, rare in the Pinacate.

96

APODIFORMES

APODIDAE - SWIFTS

Vaux's Swift (Chaetura vauxi) - Vencejo de Vaux. Common spring and fall transient

through the Colorado delta and along the coast.

White-throated Swift (Aeronautes saxatalis) - Vencejo Gorjiblanco. Fairly common

winter visitor throughout the delta. One record at Pinacate; presumed breeding at Río

Sonoyta (Russell & Monson 1998).

TROCHILIDAE - HUMMINGBIRDS

Black-chinned Hummingbird (Archilochus alexandri) - Colibrí Barbinegro.

Uncommon transient and breeder in the Río Colorado.

Anna's Hummingbird (Calypte anna) - Colibrí de Anna. Common transient through the

region. Uncommon local resident and presumed breeder at Río Colorado (Patten et al.

2001).

Costa's Hummingbird (Calypte costae) - Colibrí de Costa. Fairly common breeding

resident in the Colorado delta, Río Sonoyta, Pinacate, and Puerto Peñasco.

Calliope Hummingbird (Stellula calliope) - Colibrí de Caliope. Rare spring transient at

El Doctor and Río Sonoyta.

Rufous Hummingbird (Selasphorus rufus) - Zumbador Rufo. Uncommon spring and

rare fall transient through the coast, Pinacate, and Colorado delta.

Allen's Hummingbird (Selasphorus sasin) - Zumbador de Allen. Rare spring transient

through the coast, Río Sonoyta, and Colorado delta, more notably at El Doctor.

97

CORACIIFORMES

ALCEDINIDAE - KINGFISHERS

Belted Kingfisher (Ceryle alcyon) - Martin-Pescador Norteño. Fairly common winter

visitor and transient in the Colorado delta, Puerto Peñasco, and Río Sonoyta.

Green Kingfisher (Chloroceryle americana) - Martin-Pescador Verde. Only one record,

near Puerto Peñasco (Russell & Monson 1998).

PICIFORMES

PICIDAE - WOODPECKERS

Gila Woodpecker (Melanerpes uropygialis) - Carpintero de Gila. Common breeding

resident along Río Colorado, Río Sonoyta, Pinacate, and Puerto Peñasco.

Yellow-bellied Sapsucker (Sphyrapicus varius) - Chupasavia Vientre Amarillo. Casual

winter vagrant, with only one record at Río Hardy (Patten et al. 1993). An hybrid

between a Yellow-bellied Sapsucker and Red-breasted Sapsucker was banded at El

Doctor on October 7, 2003 (ACF).

Red-naped Sapsucker (Sphyrapicus nuchalis) - Chupasavia Nuquiroja. Rare winter

visitor along the Colorado, Hardy, and Sonoyta rivers.

Red-breasted Sapsucker (Sphyrapicus ruber) – Chupasavia Pechirroja. Casual spring

and winter vagrant, with only two spring records at El Doctor: one observed by K.

Garrett and one banded on December 13, 2003 (HIR). An hybrid between a Yellow-

bellied Sapsucker and Red-breasted Sapsucker was banded at El Doctor on October 7,

2003 (ACF).

98

Ladder-backed Woodpecker (Picoides scalaris) - Carpintero Listado. Common breeding resident along Río Colorado and the riparian and desertscrub areas of the Río

Sonoyta/Pinacate region.

Northern Flicker (Colaptes auratus) - Carpintero Collarejo. Fairly common winter visitor throughout riparian areas and mesquite stands.

Gilded Flicker (Colaptes chrysoides) - Carpintero Collarejo Desértico. Formerly an uncommon resident of the Hardy and Colorado rivers (Grinnell 1928), but no recent records. Presumed breeding along Río Sonoyta (Russell & Monson 1998) and San Felipe

(Patten et al. 2001; RAE).

PASSERIFORMES

TYRANNIDAE - FLYCATCHERS

Olive-sided Flycatcher (Contopus cooperi) - Pibí Boreal. Uncommon spring and rare fall transient through the Colorado delta.

Western Wood-Pewee (Contopus sordidulus) - Pibí Occidental. Common spring and fairly common fall transient in the Colorado delta and through the coast.

Alder Flycatcher (Empidonax alnorum) – Mosquero Pálido. Accidental spring transient.

Only one record at El Doctor on May 14, 2003 (OHH and HIR). The bird was captured, identified using wing and bill morphology measurements (Pyle 1997), and released.

Willow Flycatcher (Empidonax traillii) - Mosquero Saucero, Papamoscas Saucero. The endangered subspecies E. t. extimus formerly bred along the Río Colorado and Río Hardy

(Unitt 1987). No breeding activity has been detected since 1928, despite extensive

99 surveys being conducted from 1998-2003 (García-Hernández et al. 2001, Hinojosa-

Huerta et al. 2002a). “Western” Willow Flycatchers (E. t. adastus, E. t. brewsteri, and E. t. extimus) are common migrants during spring (May – mid June) and fall (August – early

October), conspicuous at El Doctor and willow stands of the Río Colorado.

Hammond's Flycatcher (Empidonax hammondii) - Mosquero de Hammond. Common spring transient through the coast, El Doctor, and Río Colorado.

Gray Flycatcher (Empidonax wrightii) - Mosquero Gris. Uncommon spring and fall transient and rare winter visitor at El Doctor, Río Colorado, and Río Sonoyta.

Dusky Flycatcher (Empidonax oberholseri) – Mosquero Oscuro. Rare spring transient through El Doctor and Río Colorado, with seven birds banded at El Doctor and Río

Colorado between 2002 and 2004 (OHH).

Pacific Slope Flycatcher (Empidonax difficilis) - Mosquero Occidental. The most abundant migrant flycatcher through the Colorado delta, especially in spring. Abundant at

El Doctor from mid-March to mid-May.

Black Phoebe (Sayornis nigricans) - Mosquero Negro. Common breeding resident through the Colorado delta and canals of the Mexicali Valley. Common transient and winter visitor along coastal scrub and Río Sonoyta.

Eastern Phoebe (Sayornis phoebe) – Papamoscas Fibí. Casual winter vagrant, with one record on the Colorado Desert region of Baja California (Patten et al. 2001).

Say's Phoebe (Sayornis saya) - Mosquero Llanero. Common winter visitor, especially at

Río Colorado, El Doctor, and Río Sonoyta. Presumed breeding in the Colorado delta

(Patten et al. 2001).

100

Vermilion Flycatcher (Pyrocephalus rubinus flammeus) – Brasita, Mosquero Cardenal,

Pájaro Bule, Chapaturrín. Fairly common breeding resident along riparian areas of Río

Colorado, Río Hardy, and Laguna del Indio. Apparently was almost extirpated as a breeder in the Colorado delta (Patten et al. 2001) but the local population has increased, most likely associated with revegetation of riparian areas in response to instream flows.

Ash-throated Flycatcher (Myiarchus cinerascens) - Copetón Gorjicenizo. Uncommon breeder along Río Colorado, Río Sonoyta, and desertscrub areas of San Felipe, Puerto

Peñasco, and Pinacate. Common transient and rare winter visitor.

Brown-crested Flycatcher (Myiarchus tyrannulus) Papamoscas tirano. Potential rare breeder along the Limitrophe Zone of the Colorado River, with few pairs observed in the area (Data from the Arizona Breeding Bird Atlas, September 2003, facilitated by Troy

Corman from the Arizona Game and Fish Department).

Tropical Kingbird (Tyrannus melancholicus) – Tirano Tropical. Casual winter vagrant, with only one recorded at Puerto Peñasco during the Christmas Bird Count of 2001

(National Audubon Society 2002).

Cassin's Kingbird (Tyrannus vociferans) - Tirano de Cassin. Casual vagrant, with only four records: Pozo Salado (Patten et al. 2001), Puerto Peñasco (Russell & Monson 1998),

Río Hardy (EZH and OHH, March 13, 2002), and Golfo de Santa Clara (RAE, August 3

1997).

Western Kingbird (Tyrannus verticalis) - Tirano Occidental. Common breeder throughout the Colorado delta. Presumed breeder at Río Sonoyta (Russell & Monson

1998). Common transient through the coastal desertscrub.

101

Eastern Kingbird (Tyrannus tyrannus) - Tirano Viajero. Casual vagrant, with only one recorded at Laguna Salada on June 1997 (Patten et al. 2001).

LANIIDAE - SHRIKES

Loggerhead Shrike (Lanius ludovicianus) - Lanio Americano, Alcaudón Verdugo,

Verduguillo. Fairly common breeder and common winter visitor in desertscrub and

riparian areas throughout the region.

VIREONIDAE - VIREOS

White-eyed Vireo (Vireo griseus) – Vireo Ojiblanco. Accidental spring vagrant. Only

one record from El Doctor (K. Garrett).

Bell's Vireo (Vireo bellii) - Vireo de Bell. Formerly was a common breeder along Río

Colorado (Rosenberg et al. 1991), now a rare summer resident in the remnant riparian

patches of the Colorado, with unconfirmed breeding. Uncommon spring transient through

El Doctor and Río Colorado.

Gray Vireo (Vireo vicinior) - Vireo Gris. Uncommon winter visitor and transient at

coastal and lowland desertscrub areas of the Río Sonoyta/Puerto Peñasco/Pinacate region

(Bates 1992, Russell & Monson 1998). Only one record for San Felipe (Grinnell 1928).

Plumbeous Vireo (Vireo plumbeus) - Vireo Plomizo. Common transient and uncommon

winter visitor to Río Colorado and El Doctor.

Cassin's Vireo (Vireo cassinii) - Vireo de Cassin's. Uncommon winter visitor and

transient at Río Colorado, El Doctor, Río Sonoyta, and Puerto Peñasco.

Hutton’s Vireo (Vireo huttoni) – Vireo Reyezuelo. Rare transient and winter visitor at

Río Sonoyta and El Doctor.

102

Warbling Vireo (Vireo gilvus) - Vireo Gorgojeador. Very abundant fall and spring transient at El Doctor, Río Colorado, and Río Sonoyta.

Red-eyed Vireo (Vireo olivaceus) – Vireo Ojirrojo. Accidental spring vagrant. Only one record from El Doctor (K. Garrett).

CORVIDAE – CROWS AND JAYS

Clark's Nutcracker (Nucifraga colombiana) - Cascanueces Americano. The only record is of a skull found near Puerto Peñasco on 1972 (Russell & Monson 1998).

American Crow (Corvus brachyrhynchos) - Cuervo Americano. Casual winter vagrant

along Río Colorado and Mexicali Valley, usually in large flocks.

Common Raven (Corvus corax) - Cuervo Grande. Fairly common breeding resident

throughout the region.

ALAUDIDAE - LARKS

Horned Lark (Eremophila alpestris) - Alondra Cornuda. Fairly common breeding

resident and common winter visitor throughout the Colorado delta, Puerto Peñasco, and

Río Sonoyta.

HIRUNDINIDAE - SWALLOWS

Purple Martin (Progne subis) - Martín Azul. Rare spring transient through El Doctor,

Ciénega de Santa Clara, and Puerto Peñasco.

Tree Swallow (Tachycineta bicolor) - Golondrina Arbolera. Common transient and

winter visitor through the Colorado delta, coastal areas, and Río Sonoyta.

Violet-green Swallow (Tachycineta thalasssina) - Golondrina Cariblanca. Fairly

common spring transient and uncommon winter visitor and fall transient through the

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Colorado delta, coastal areas, and Río Sonoyta. Locally breeds along cliffs near Laguna

Salada at least during wet years (Patten et al. 2001).

Northern Rough-winged Swallow (Stelgidopteryx serripennis) - Golondrina Aliserrada

Norteña. Common transient through the Colorado delta and coastal areas. Common breeder in the Mexicali Valley and Río Sonoyta.

Bank Swallow (Riparia riparia) - Golondrina Ribereña. Uncommon transient along Río

Colorado, Ciénega de Santa Clara, El Doctor, and the coast.

Cliff Swallow (Petrochelidon pyrrhonota) - Golondrina Risquera. Common breeder under bridges in the Río Colorado, Mexicali Valley, and Río Sonoyta. Common transient through the delta and coastal areas.

Barn Swallow (Hirundo rustica) - Golondrina Ranchera. Common spring and fall transient through Río Colorado, Ciénega de Santa Clara, El Doctor, Río Sonoyta, and the coast.

REMIZIDAE - VERDINS

Verdin (Auriparus flaviceps) – Baloncillo. Common breeding resident throughout the

region.

SITTIDAE - NUTHATCHES

Red-breasted Nuthatch (Sitta canadensis) – Saltapalos Canadiense. Casual spring

vagrant, with only one record at El Doctor (K. Garrett).

White-breasted Nuthatch (Sitta carolinensis) – Saltapalos Pechiblanco. Casual winter

and spring vagrant, with only one recorded at Puerto Peñasco during the Christmas Bird

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Count of 2001 (National Audubon Society 2002) and one at Río Colorado on May 24,

2003 (HIR).

CERTHIIDAE - CREEPERS

Brown Creeper (Certhia americana) - Trepador Americano. Casual winter visitor at

Puerto Peñasco, with only two records (Russell & Monson 1998).

TROGLODYTIDAE - WRENS

Cactus Wren (Campylorhynchus brunneicapillus) - Matraca Desértica. Common

breeding resident throughout the region.

Rock Wren (Salpinctes obsoletus) - Saltapared Roquero. Uncommon breeding resident

in San Felipe, Sierra Cucapá, El Golfo de Santa Clara, and Puerto Peñasco (Patten et al.

2001, Russell & Monson 1998). Rare winter visitor throughout the delta, Río Sonoyta, and Pinacate.

Canyon Wren (Catherpes mexicanus) - Saltapared Barranquero. Rare breeding resident at cliffs and small canyons around Río Sonoyta, Puerto Peñasco, and Pinacate. Rare

winter visitor in rocky areas of the Colorado Desert region of Baja California.

Bewick's Wren (Thryomanes bewickii) - Saltapared de Bewick. Fairly common winter

visitor throughout the Colorado delta, the coast, and Río Sonoyta.

House Wren (Troglodytes aedon) – Saltapared Continental Norteño. Uncommon winter visitor and spring transient through the region.

Sedge Wren (Cistothorus platensis) - Saltpared Sabanero. Only one recorded at El

Doctor on December 1983 (Peter Pyle and Steve Howell in Russell & Monson 1998).

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Marsh Wren (Cistothorus palustris) - Saltapared Pantanero. Common breeding resident at Ciénega de Santa Clara, El Doctor, and agricultural drains of the Mexicali Valley with emergent vegetation. Common winter visitor at Puerto Peñasco and Río Sonoyta.

REGULIDAE - KINGLETS

Ruby-crowned Kinglet (Regulus calendula) - Reyezuelo Sencillo. Common winter

visitor through the region.

SYLVIIDAE - GNATCATCHERS

Blue-gray Gnatcatcher (Polioptila caerulea) - Perlita Grisilla. Fairly common winter

visitor at Río Colorado, El Doctor, Río Sonoyta, and Puerto Peñasco.

California Gnatcatcher (Polioptila californica) - Perlita Californiana. Uncommon

resident near south end of Bahía San Felipe (Mellink & Rea 1994).

Black-tailed Gnatcatcher (Polioptila melanura) - Perlita Colinegra. Common breeding

resident at Río Colorado, El Doctor, Río Sonoyta, Pinacate, and Puerto Peñasco.

TURDIDAE - THRUSHES

Western Bluebird (Sialia mexicana) - Azulejo Gorjiazul. Rare and irregular winter

visitor to Río Sonoyta (Russell & Monson 1998), Río Colorado, and San Felipe (Patten et

al. 2001).

Mountain Bluebird (Sialia currucoides) - Azulejo Pálido. Rare and irregular winter

visitor throughout the region.

Townsend’s Solitaire (Myadestes townsendi) – Clarín Norteño. Rare winter visitor at

Río Sonoyta.

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Swainson's Thrush (Catharus ustulatus) - Zorzalito de Swainson. Common spring and uncommon fall transient through El Doctor, Río Colorado, and coastal desertscrub.

Hermit Thrush (Catharus guttatus) - Zorzalito Colirrufo. Fairly common transient and winter visitor at El Doctor, Río Colorado, and Río Sonoyta.

American Robin (Turdus migratorius) - Zorzal Petirrojo. Uncommon and irregular winter visitor through the region. One summer record at Mexicali on July 8, 2003 (RAE).

MIMIDAE – MOCKINGBIRDS AND THRASHERS

Gray Catbird (Dumetella carolinensis) – Maullador Gris. Accidental spring vagrant,

with one individual banded at El Doctor in May 17, 2004, and recaptured on May 27,

2004 at the same site (HIR).

Northern Mockingbird (Mimus polyglottos) - Cenzontle Norteño. Common breeding

resident throughout the region.

Sage Thrasher (Oreoscoptes montanus) - Cuitlacoche de Artemesia. Uncommon spring

transient and winter visitor through the region.

Brown Thrasher (Toxostoma rufum) – Cuitlacoche Rojizo. Only one recorded at Puerto

Peñasco on 1981 (Russell & Monson 1998).

Bendire's Thrasher (Toxostoma bendirei) - Cuitlacoche de Bendire. Uncommon winter

visitor to Río Sonoyta/Pinacate region. Casual winter vagrant to Río Colorado, with only

one record (Daniels et al. 1993).

Curve-billed Thrasher (Toxostoma curvirostre) - Cuitlacoche Piquicurvo. Uncommon

breeding resident at Río Sonoyta, Pinacate, Puerto Peñasco, and El Golfo de Santa Clara.

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Crissal Thrasher (Toxostoma crissale) - Cuitlacoche Crisal. Fairly common breeding resident at Río Colorado. Uncommon winter visitor to Pinacate and Río Sonoyta.

Le Conte's Thrasher (Toxostoma lecontei) - Cuitlacoche Pálido. Uncommon breeding resident around the open desertscrub regions.

MOTACILLIDAE – WAGTAILS AND PIPITS

American Pipit (Anthus rubescens) - Bisbita Americana. Common winter visitor

throughout the Colorado delta, coastal areas, and Río Sonoyta.

BOMBYCILLIDAE - WAXWINGS

Cedar Waxwing (Bombicylla cedrorum) - Ampelis Americano. Uncommon and

irregular winter visitor to Río Colorado, Puerto Peñasco, and Río Sonoyta.

PTILOGONATIDAE – SILKY FLYCATCHERS

Phainopepla (Phainopepla nitens) - Capulinero Negro. Fairly common breeding resident in the remnant mesquite patches of the Colorado delta, Río Sonoyta, and Pinacate.

PARULIDAE – WOOD-WARBLERS

Orange-crowned Warbler (Vermivora celata) - Chipe Corona-Naranja. Common

transient and winter visitor, most commonly found at El Doctor, Río Colorado, and Río

Sonoyta.

Nashville Warbler (Vermivora ruficapilla) - Chipe de Nashville. Common spring and

uncommon fall transient at El Doctor, Río Colorado, and coastal areas of Río Sonoyta.

Casual in winter, with only two records (Patten et al. 2001).

Lucy's Warbler (Vermivora luciae) - Chipe de Lucy. Formerly a common breeder

throughout the Colorado delta (Russell & Monson 1998), but no recent breeding records.

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Presumed breeding near Sonoyta (Russell & Monson 1998). Rare transient through Río

Colorado, El Doctor, and along the coast.

Yellow Warbler (Dendroica petechia) - Chipe Amarillo. Formerly a common breeding resident in the Colorado delta (Grinnell 1928, van Rossem 1945), is now a rare summer visitor with unconfirmed breeding. Common transient through El Doctor, Río Colorado, and Río Sonoyta. Rare winter visitor, with only two records at Puerto Peñasco (Russell &

Monson 1998) and two at the Mexicali Valley (Patten et al. 2001; RAE, January 2003).

Cape May Warbler (Dendroica tigrina) - Chipe Atigrado. Accidental winter vagrant.

Only one recorded at Puerto Peñasco on December 1989 (David Stejskal in Russell &

Monson 1998).

Black-throated Blue Warbler (Dendroica caerulescens) – Chipe Azulnegro. Accidental fall vagrant. Only one recorded at Río Sonoyta on October 1975 (Groschupf et al. 1988).

Yellow-rumped Warbler (Dendroica coronata) - Chipe Rabadilla Amarilla. Common transient and winter resident in the Colorado delta, Río Sonoyta, Pinacate, and coastal desertscrub.

Black-throated Gray Warbler (Dendroica nigrescens) - Chipe Negrigris. Fairly common spring and uncommon fall transient through El Doctor, Río Colorado, and

Puerto Peñasco.

Townsend's Warbler (Dendroica towsendi) - Chipe de Townsend. Fairly common spring transient through the coastal desertscrub, El Doctor, and Río Colorado. The species has been recorded three times during winter at Puerto Peñasco (Russell &

Monson 1998).

109

Hermit Warbler (Dendroica occidentales) - Chipe Cabeciamarillo. Uncommon spring transient through El Doctor and Río Colorado.

Yellow-throated Warbler (Dendroica dominica) – Chipe Garganta Amarilla. Accidental spring vagrant. Only one recorded at Quitovac (about 40 kilometers southeast of

Sonoyta) on May 1982 (Amadeo Rea in Russell & Monson 1998).

Prairie Warbler (Dendroica discolor) – Chipe Pradeño. Accidental fall vagrant. Only one observed at El Doctor on October 1999 (van Riper III et al. 1999).

Palm Warbler (Dendroica palmarum) - Chipe Playero. Accidental winter vagrant. Ten birds were observed at El Doctor on December 1983 (Peter Pyle and Steve Howell in

Russell & Monson 1998), and three at Puerto Peñasco on December 1993 (Steve Ganley in Russell & Monson 1998).

American Redstart (Setophaga rutinilla) - Pavito Migratorio. Casual transient, with one recorded at Sonoyta on November 1968 (R. Cunningham in Russell & Monson 1998) and two at El Doctor: on September 17, 2002 (HIR) and September 26, 2003(banded; ACF).

Ovenbird (Seiurus aurocapillus) – Chipe suelero. Accidental spring vagrant. Only one recorded, at El Doctor in May 2002 (OHH and EZH.).

Northern Waterthrush (Seiurus noveboracensis) – Chipe Charquero. Accidental fall vagrant. Only one recorded (banded) at El Doctor in November 8, 2003 (ACF).

Macgillivray's Warbler (Oporornis tolmiei) - Chipe de Tolmie. Fairly common spring and fall transient through coastal desertscrub, Río Sonoyta, El Doctor, and Río Colorado.

110

Common Yellowthroat (Geothlypis trichas) - Mascarita Común. Common breeding resident at the Hardy and Colorado rivers, Ciénega de Santa Clara, and El Doctor.

Common transient and winter visitor at Río Sonoyta and Puerto Peñasco.

Hooded Warbler (Wilsonia citrine) – Chipe Encapuchado. Accidental spring vagrant, with one individual banded at El Doctor in June 12, 2004 (HIR).

Wilson's Warbler (Wilsonia pusilla) - Chipe de Wilson. The most abundant of the migrant warblers. Common spring and fall transient through coastal desertscrub, El

Doctor, Río Sonoyta, and Río Colorado.

Canada Warbler (Wilsonia canadensis) – Chipe de Canadá. Accidental spring vagrant, with one individual banded at El Doctor in May 27, 2004 (HIR). This is the first record in the state of Sonora.

Yellow-breasted Chat (Icteria virens) - Gritón Pechiamarillo. Uncommon breeder along

Río Hardy and Río Colorado. Uncommon spring and fall transient through coastal desertscrub, El Doctor, and Río Colorado.

THRAUPIDAE - TANAGERS

Summer Tanager (Piranga rubra) - Tángara Roja. Formerly a common breeder along

the Hardy and Colorado rivers (Grinnell 1928, Miller et al. 1957), but no recent breeding

activity has been documented. Only three recent records, a female at the Río Hardy on

April 1984 (Patten et al. 2001), a male at Río Colorado in September 1999 (van Riper III

et al. 1999), and a second year male, banded at Río Colorado in May 26, 2004 (HIR).

Western Tanager (Piranga ludoviciana) - Tángara Occidental. Common spring and fall

transient through coastal desertscrub, El Doctor, Río Sonoyta, and Río Colorado.

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EMBERIZIDAE – TOWHEES, SPARROWS, AND LONGSPURS

Green-tailed Towhee (Pipilo chlorurus) - Rascador Coliverde. Uncommon transient and

winter visitor along Río Colorado and Río Sonoyta.

Spotted Towhee (Pipilo maculates) - Rascador Pinto. Rare winter visitor at San Felipe

(Patten et al. 2001), El Golfo de Santa Clara, Río Colorado (OHH) and Puerto Peñasco

(Russell & Monson 1998).

Canyon Towhee (Pipilo fuscus) - Rascador Arroyero. Common resident along Río

Sonoyta, where breeding is presumed (Russell & Monson 1998).

Abert's Towhee (Pipilo aberti) - Rascador de Abert. Common breeding resident

throughout the Colorado delta, especially along Río Colorado.

Cassin's Sparrow (Aimophila cassinii) - Zacatonero de Cassin. Casual spring vagrant.

Recorded once north of Puerto Peñasco (Russell & Monson 1998).

Rufous-crowned Sparrow (Aimophila ruficeps) – Zacatonero Corona Rufa. Rare

resident near Sonoyta, where breeding is presumed (Russell & Monson 1998).

Chipping Sparrow (Spizella passerina) - Gorrión Cejiblanco. Uncommon winter visitor

and transient throughout the Colorado delta, Puerto Peñasco, and Río Sonoyta.

Clay-colored Sparrow (Spizella pallida) - Gorrión Pálido. Casual transient. Only one

bird recorded, at Puerto Peñasco (Russell & Monson 1998).

Brewer’s Sparrow (Spizella breweri) - Gorrión de Brewer. Common winter visitor

throughout the region.

Vesper Sparrow (Poocetes gramineus) - Gorrión Coliblanco. Uncommon winter visitor

at Río Colorado and Río Sonoyta.

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Lark Sparrow (Chondestes grammacus) - Gorrión Arlequín. Fairly common winter visitor to the Colorado delta and Puerto Peñasco. Breeding might occur in the Mexicali

Valley (Patten et al. 2001).

Black-throated Sparrow (Amphispiza bilineata) - Gorrión Gorjinegro. Uncommon breeding resident in desertscrub areas, in both the Colorado Desert region in Baja

California (Patten et al. 2001) and the Pinacate region in Sonora (Russell & Monson

1998).

Sage Sparrow (Amphispiza belli) - Gorrión de Artemesia. Fairly common winter visitor at coastal dunes, open creosote bush, and saltbush communities throughout the region

(Russell & Monson 1998).

Lark Bunting (Calamospiza melanocorys) - Gorrión Alipálido. Rare winter visitor and spring transient, with three records near San Felipe (Patten et al. 2001) and four near

Puerto Peñasco (Russell & Monson 1998).

Savannah Sparrow (Passerculus sandwichensis) - Gorrión Sabanero. Common winter visitor throughout the region. The Large-billed Savannah Sparrow (P. s. rostratus) is a common breeder at Isla Montague, Cerro Prieto, Ciénega de Santa Clara, El Doctor, and coastal salt marshes, although is threatened and declining (Mellink & Ferreira-Bartrina

2000). P. s. rostratus, is under special protection in México (Diario Oficial de la

Federación 2002).

Grasshopper Sparrow (Ammodramus savannarum) - Gorrión Chapulín. Casual winter vagrant, with one record north of San Felipe (Patten et al. 2001) and one north of Puerto

Peñasco (Russell & Monson 1998).

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Fox Sparrow (Passerella iliaca) - Gorrión Rascador. Casual winter visitor. Two records in the Mexicali Valley (Patten et al. 2001) and one in the Río Sonoyta (Russell &

Monson 1998).

Song Sparrow (Melospiza melodia) - Gorrión Cantor. Common breeding resident throughout the Colorado delta.

Lincoln's Sparrow (Melospiza lincolnii) - Gorrión de Lincoln. Fairly common winter visitor to the Colorado delta, coastal desertscrub, and Río Sonoyta.

Swamp Sparrow (Melospiza georgiana) - Gorrión Pantanero. Rare winter visitor along coastal marshes, Río Sonoyta, and Río Colorado.

White-throated Sparrow (Zonotrichia albicollis) - Gorrión Gorjiblanco. Casual winter visitor near Puerto Peñasco; only recorded once (Russell & Monson 1998).

White-crowned Sparrow (Zonotrichia leucophrys) - Gorrión Coroniblanco. Common winter visitor and transient throughout the region.

Golden-crowned Sparrow (Zonotrichia atricapilla) - Gorrión Coronidorado. Rare winter visitor, one record at Mexicali (Patten et al . 2001) and another near Puerto

Peñasco (Russell & Monson 1998).

Dark-eyed Junco (Junco hyemalis) - Junco Ojioscuro. Uncommon winter visitor at

Colorado delta, Puerto Peñasco, and Río Sonoyta.

McCowns’s Longspur (Calcarius mccownii) – Escribano de McCown. Accidental winter visitor, with four individuals observed on December 8, 2004 at the Mesa de

Andrade dunes (OHH).

114

Chestnut-Collared Longspur (Calcarius ornatos) - Escribano Cuellicastaño. Casual winter visitor, with a flock of more than 50 birds observed at Río Colorado on November

1994 (Patten et al. 2001) and a flock of 24 recorded at Puerto Peñasco in October 1976

(Russell & Monson 1998).

CARDINALIDAE - CARDINALS

Northern Cardinal (Cardinalis cardinalis) - Cardenal Norteño. Uncommon resident

around Puerto Peñasco and Sonoyta, where breeding is presumed (Russell & Monson

1998). Only one record at Río Colorado, 6 km south of Morelos Dam (May 6, 2003;

OHH).

Pyrrhuloxia (Cardinalis sinuatus) - Cardenal Desértico. Rare summer resident around

Puerto Peñasco and Sonoyta; breeding is presumed in the last (Russell & Monson 1998).

Rose-breasted Grosbeak (Pheucticus ludovicianus) – Picogordo Pecho Rosa. Casual

spring vagrant, with three records at El Doctor (K. Garrett in April 1999; EZH in May 17,

2002; OHH in May 20, 2003, this bird was captured, photographed, and released).

Black-headed Grosbeak (Pheucticus melanocephalus) - Picogrueso Tigrillo. Common spring and uncommon fall transient through El Doctor, Río Sonoyta, and Río Colorado.

Blue Grosbeak (Guiraca caerulea) - Picogrueso Azul. Common breeder along riparian areas of Río Colorado.

Lazuli Bunting (Passerina amoena) - Colorín Lazulita. Fairly common spring transient through coastal desertscrub and El Doctor; uncommon thoughout the Mexicali Valley.

Indigo Bunting (Passerina cyanea) - Colorín Azul. Casual spring vagrant, with one

recorded at El Doctor on April 2002 (OHH and EZH).

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Painted Bunting (Passerina ciris) - Colorín Sietecolores. Accidental winter vagrant. One male was collected near Puerto Peñasco in December 1965 (Russell & Monson 1998).

ICTERIDAE - BLACKBIRDS

Red-winged Blackbird (Agelaius phoeniceus) - Tordo Sargento. Common breeding

resident throughout the Colorado delta. Common winter visitor at Puerto Peñasco and

Río Sonoyta. The population of this species has increased over the last decades in relation

to increased agriculture in the region.

Eastern Meadowlark (Sturnella magna) - Pradero Común. Casual winter vagrant, with

only three records from Puerto Peñasco (Russell & Monson 1998).

Western Meadowlark (Sturnella neglecta) - Pradero Occidental. Fairly common

breeding resident, especially at El Doctor, Ciénega de Santa Clara, and alfalfa fields of

the Mexicali Valley. Common winter visitor throughout the region.

Yellow-headed Blackbird (Xanthocephalus xanthocephalus) - Tordo Cabeciamarillo.

Fairly common breeding resident, especially at Ciénega de Santa Clara. Common winter

visitor throughout the region.

Rusty Blackbird (Euphagus carolinus) - Tordo Canadiense. Accidental, with only one

record near Puerto Peñasco (Russell & Monson 1998).

Brewer's Blackbird (Euphagus cyanocephalus) - Tordo de Brewer. Common winter

visitor throughout the Colorado delta, Puerto Peñasco, and Río Sonoyta. Only two

records of summer birds (Ruiz-Campos & Rodríguez-Meraz 1997).

116

Great-tailed Grackle (Quiscalus mexicanus) - Zanate Mayor. Common breeding resident throughout most of the region. Most abundant around agricultural fields and towns.

Bronzed Cowbird (Molothrus aenus) - Vaquero Ojirojo. Rare summer resident, presumed breeding at Río Colorado and Puerto Peñasco. We observed displaying males at Río Colorado (April 2002, HIR), at Ejido Johnson near the Ciénega de Santa Clara

(May 2002, EZH), and Ejido Pachuca near Morelos Dam (June 2003, OHH). Rare winter visitor, with 9 birds recorded in the Mexicali Valley on January 13, 2003 (RAE).

Brown-headed Cowbird (Molothus ater) - Vaquero Cabecicafé. Common breeding resident throughout the Colorado delta, Puerto Peñasco, and Río Sonoyta, with numbers augmented in winter. Populations of this cowbird have increased with farming activity in the region.

Hooded Oriole (Icterus cucullatus) - Bolsero Cuculado. Fairly common breeder along the riparian areas of Río Colorado. Presumed breeding near Sonoyta (Russell & Monson

1998).

Bullock's Oriole (Icterus bullockii) - Bolsero de Bullock. Common breeder along Río

Colorado. Common transient through Puerto Peñasco, Río Sonoyta, and El Doctor.

Baltimore Oriole (Icterus galbula) – Bolsero de Baltimore. Accidental spring vagrant, with only one recorded (banded) at El Doctor on May 30, 2004 (HIR).

Scott's Oriole (Icterus parisorum) - Bolsero Tunero. Rare spring transient and winter visitor, and uncommon breeder around San Felipe and the Colorado Desert region of Baja

California (Patten et al. 2001).

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FRINGILLIDAE - FINCHES

Purple Finch (Carpodacus purpureus) - Fingílido Purpureo. Accidental winter vagrant,

with only one bird recorded at the 1995 Christmas Bird Count of Puerto Peñasco (S.

Ganley).

Cassin’s Finch (Carpodacus cassinii) – Fringílido de Cassin. Accidental winter vagrant.

Only one record from Puerto Peñasco in December 2001 (National Audubon Society

2002).

House Finch (Carpodacus mexicanus) - Fringílido Mexicano. Common breeding resident throughout the region.

Pine Siskin (Carduelis pinus) - Dominico Pinero. Rare and irregular winter visitor, with three records from the Colorado delta region (Grinnell 1928, Patten et al. 1993, Ruiz-

Campos & Rodríguez-Meraz 1997), one from Puerto Peñasco, and one from Sonoyta

(Russell & Monson 1998).

Lesser Goldfinch (Carduelis psaltria) - Dominico Dorsioscuro. Fairly common winter visitor throughout the region and uncommon breeder along Río Colorado.

Lawrence's Goldfinch (Carduelis lawrencei) - Dominico de Lawrence. Rare transient and casual winter visitor at Puerto Peñasco, Río Sonoyta, Río Hardy, Sierra Cucapá, and

Sierra las Pintas (south of Sierra Cucapá), where was recorded breeding only once (Patten et al. 2001).

American Goldfinch (Carduelis tristis) - Dominico Americano. Probably a rare winter visitor, only two records, near La Ventana (Patten et al. 2001) and near Sonoyta (Russell

& Monson 1998).

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NON-NATIVE SPECIES

Ring-necked Pheasant (Phasianus colchicus) - Faisán de Collar. Common breeding resident in the Mexicali Valley.

Rock Dove (Feral Pigeon) (Columba livia) - Paloma Doméstica. Common breeding resident, even colonizing pipes through the levee system of the Río Colorado.

Eurasian Collared-Dove (Streptopelia decaocto) – Paloma de Collar. Detected recently in the Mexicali Valley (2003; RAE), probable expanding and increasing its numbers in the region.

European Starling (Sturnus vulgaris) - Estornino Europeo. Common breeding resident around urban areas and farms. Reached the Mexicali Valley in the 1950s (Cardiff 1961).

House Sparrow (Passer domesticus) - Gorrión Doméstico. Common breeding resident throughout the region, especially around cities and towns. Probably reached the Mexicali

Valley after 1910 (Patten et al. 2001).

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APPENDIX B

DENSITIES, SPECIES RICHNESS AND HABITAT RELATIONSHIPS OF THE

AVIAN COMMUNITY IN THE COLORADO RIVER, MEXICO

Manuscript prepared for submission to the journal The Condor

120

Avian Community of the Colorado River, Mexico

DENSITIES, SPECIES RICHNESS AND HABITAT RELATIONSHIPS OF THE

AVIAN COMMUNITY IN THE COLORADO RIVER, MEXICO

Osvel Hinojosa-Huerta1,2

Helena Iturribarría-Rojas2

Enrique Zamora-Hernández2

Alejandra Calvo-Fonseca2

1104 Biological Sciences East

School of Natural Resources, University of Arizona

Tucson, AZ 85721

e-mail: [email protected]

2Pronatura Noroeste, Avenida Jalisco 903,

San Luis Río Colorado, Sonora, México. 83440.

121

Abstract. We determined the spatial and temporal patterns of avian species richness and density and explored their relationships with habitat features in the floodplain of the Colorado River in Mexico, which was subject to regeneration through pulse-floods in the last 20 years. Our work included monthly point counts at 30 transects

(240 points) from May 2002 to July 2003. The average abundance per point was 29.2 individuals (± 1.2) with an average richness of 8.6 species (± 0.2), and an average density of 47.7 birds per ha (± 7.0). The most common species were Mourning Doves, Red- winged Blackbirds, and Brown-headed Cowbirds, but another 64 species were commonly found, including Verdins, Song Sparrows, and Abert’s Towhees. Surface water was the most important habitat feature related to avian richness and density regardless of vegetation type or land cover (P < 0.005). During summer, species richness was explained by variations in water and the cover of cottonwoods (r2 = 0.56, P < 0.001), and the variation in bird densities was explained by variations in water and the cover of willows (r2 = 0.35, P = 0.003). The dedication of instream flows and pulse floods, the maintenance of vegetation cover and structural diversity, and an increase of older riparian

stands will secure the viability of existing bird populations and will increase the

probability of recovery of the species that are still extirpated from the floodplain of the

Colorado River in Mexico.

Key words: birds, Colorado River delta, cottonwood, floodplain, riparian, water,

willow.

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INTRODUCTION

The recovery of ecosystem functions in degraded riparian areas has become one of the major conservation goals throughout North America (Rich et al. 2003). In western North

America, about 95% of riparian areas have been destroyed, altered, or degraded by human activities (Ohmart 1994). Yet, these riparian ecosystems maintain the highest numbers of bird species and densities in the region (Knopf et al. 1988, Rosenberg et al.

1991), providing critical breeding grounds, wintering and stopover areas and migratory corridors (Ohmart and Anderson 1986, Knopf and Samson 1994, Skagen et al. 2005).

Thus, the resulting cumulative effect of habitat loss in riparian areas through the life cycle of birds has become one of the most important causes for land bird population declines in western North America (DeSante and George 1994, Hutto 2000, Norris et al.

2004).

Multiple efforts have been triggered to understand the biotic responses of riparian ecosystems to regeneration events. Results of these studies emphasize the importance of maintaining a natural pulse flood regime, the dynamic geomorphologic processes in the floodplains, and a diverse mosaic of habitat structures (Gore 1985, Richter and Richter

2000, Stromberg and Chew 2002, Glenn et al. 2001).

The response of avian diversity and abundance to restoration efforts has been documented, showing a positive relationship with an increase of cottonwood (Populus fremontii) and willow (Salix gooddingii) cover and an increase in the structural complexity of vegetation (Scott et al. 2003, Krueper et al. 2003, Anderson et al. 2004).

However, the success of revegetation (planting) efforts in restoring riparian ecosystem

123 functions and the native avifauna has been limited. Revegetated sites were found to have lower avian diversity, densities, and reproductive success than sites under natural regeneration processes, as a result of lower habitat diversity, structure, and unnatural patterns of hydrology (Larison et al. 2001, Snell-Rood and Cristol 2003).

Other scientists have suggested that more natural revegetation can be stimulated by releasing water from upstream reservoirs in short pulses (Richter and Richter 2000,

Sher et al. 2000, Stromberg and Chew 2002, Glenn and Nagler 2005). However, questions remain whether a degraded floodplain can be enhanced with a designed pulse- flood regime, and whether and how the avian community responds to such regeneration events.

The floodplain of the Colorado River in Mexico is a degraded environment.

Before the development of the hydraulic infrastructure in the basin, the Colorado River delta supported over 200 000 hectares of riparian and wetland areas (Sykes 1937). After the completion of the larger dams in the basin in the 1930s, no base or pulse flow reached the area for nearly 50 years, causing the virtual disappearance of the cottonwood and willow forest and the invasion of the exotic saltcedar (Tamarix ramosissima; Glenn et al.

2001). This caused the local extirpation of nine breeding species, including Southwestern

Willow Flycatcher, Yellow Warbler, and Bell’s Vireo (Hinojosa-Huerta et al. 2004).

However, a modest but significant portion of the riparian ecosystem in the floodplain of the Colorado River in Mexico has been regenerated in response to large- volume water releases from U.S. dams over the past 25 years (Glenn et al. 2001, Zamora-

Arroyo et al. 2005). The releases have simulated a natural pulse-flood regime and a base

124 flow, thus maintaining young and dynamic stands of cottonwood and willows, which have covered over 3000 ha despite the dominant presence of saltcedar (Nagler et al.

2005).

Our work targeted two main issues relevant to avian ecology and restoration of riparian systems: 1) we determined the spatial and temporal patterns of species richness, abundance, and community structure in a degraded floodplain that was subject to regeneration through pulse-floods; and 2) we explored the relationships of species richness, density and community structure with land cover and vegetation features.

Finally, with this information we analyzed the restoration options for the floodplain of the

Colorado River in Mexico.

METHODOLOGY

STUDY AREA

The study area encompasses the floodplain of the Colorado River in Mexico, from San

Luis Río Colorado downstream to the confluence of the Colorado with the Hardy River

(Figure 1). The floodplain traverses the Mexicali Valley as the river flows toward the

Gulf of California, and is surrounded by flood control levees on each margin. The total area is 43 000 ha, and extends for 150 river kilometers. This includes the main stem of the Colorado, secondary streams, backwater lagoons, and the portion of the major agricultural drains that are within the floodplain.

Water flows in the area have been intermittent since the completion of Hoover

Dam (1937), depending upon excess deliveries from the U.S. to Mexico, and operational

125 releases from the Mexicali Irrigation District and agricultural drainage water. Extended dry periods have occurred (1952-1979), in which no flows reached the area, as well as extreme flooding events (1981-1983) of over 2000 m3 s-1. During the last 12 years, the

area has experienced significant flooding events (1993, 1998, 2002, and 2005) in the

magnitude of 40-100 m3 s-1, as well as modest semi-continuous instream flows (2-8 m3 s-1) during several years (1993, 1997, 1998, 1999, 2001, 2002, and 2004; Zamora-Arroyo et al. 2005).

Two different sections can be distinguished in the floodplain during its progression towards the Gulf of California, with important changes in vegetation structure, species composition, hydrology, and water quality (Figure 2). From north to south, the first section goes from San Luis Río Colorado to the Railroad Bridge. This

stretch of the river is narrow and sparsely vegetated, but contains some dense thickets of willow. Older plants reach 8-15 m, although most are less than 4 m in height.

Cottonwood trees are also found along this reach, but they appear only as isolated individuals. Saltcedar dominates the mid- and understory over most of the area.

The second portion ends with the southernmost stands of cottonwoods and

willows along the river corridor. Although numerous pockets of cottonwood and willow

are still found along the main river channel, they constitute a lower proportion of the

riparian vegetation than that found in the upper stretches of the river. Over 70% of this

zone is dominated by a mixture of saltcedar, mesquite (Prosopis glandulosa and P. pubescens), and significant numbers of large saltbush (Atriplex spp.) plants.

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BIRD SURVEYS

We conducted bird counts following a variable distance point count methodology (Ralph et al. 1996). The counts were conducted monthly for 15 months (May 2002 – July 2003) on 30 transects randomly distributed along the floodplain (Figure 3). The whole levee system extends for 189 km. The initial point of each transect was selected by randomly picking 30 kilometer numbers (between 0 and 189, and at least 2 km apart from each other), which correspond to the km of the levee where a particular transect was started.

Each transect was composed of 8 point counts (200 m apart), and extended for 1.6 km, starting at the levee, and moving toward the main channel of the river. Transects were run by teams of two persons starting at sunrise and continuing until no later than 4 hours after sunrise. At each survey station we counted all birds heard or seen within a 5 min period, estimating distance to the observer and annotating the time at which it was detected. The position at each station (UTM, NAD 1927 Mexico) was recorded using a handheld GPS receiver (Garmin Etrex).

HABITAT SURVEYS

We measured habitat features in the 30 survey transects. At each station we estimated the percent ground coverage, and the minimum, maximum, and average height of each of the following strata: trees (vegetation >3 m in height), shrubs (0.5 – 3 m), herbs (0.1 – 0.5 m), forbs (< 0.1 m), emergent plants, bare soil, and open water. We then categorized each stratum by estimating the percent coverage and average height of each plant species within a stratum. For open water, we recorded type (primary or secondary stream, drain,

127 irrigation canal, or lagoon), depth, and width. The estimates of land cover were obtained with the aid of measuring tapes, the GPS receivers, and pacing.

STATISTICAL ANALYSES

All the data were entered in a relational database in MS Access. Statistical analyses were conducted using JMP IN 3.2 (Sall and Lehman 1996). Detections of flyover birds were excluded from the analyses. Bird densities were estimated using DISTANCE (Thomas et al. 2002). Distance models were selected using a combination of Akaike’s Information

Criterion, Goodness of Fit test, and the coefficient of variation in the parameter estimates.

Estimates of abundance were obtained considering the study area of the point count surveys (12 630 ha), and the 95% confidence intervals of the density estimates from

DISTANCE.

The comparison of richness and density among seasons was performed using

ANOVA and a Turkey-Kramer pairwise comparison. The grouping of visits by season was based on the pattern of temporal shift in the avian community, considering Spring

(March, April, May), Summer (June, July, August), Fall (September, October,

November), and Winter (December, January, February).

The habitat relationships were determined with a multiple linear regression of the measured avian parameters (densities and richness) with habitat features. For avian density, we estimated the overall density of birds per transect per visit. For species richness, we used the average species/point at each transect, for each visit.

128

We tested for pairwise correlation of explanatory variables (habitat features). If two variables were correlated >0.75, we excluded the variable with less value in management or ecological terms. We conducted a forward stepwise selection of variables for each model (P < 0.25) and ran the models including only variables with P < 0.05. The values reported in the Results are means ± SE, except for estimates of density, where

95% confidence intervals are given. We used a significance level of 0.05 for all statistical tests.

RESULTS

VEGETATION COVER

Between May 2002 and July 2003, the floodplain of the Colorado River in Mexico supported a diverse array of riparian habitat types, with vegetation cover of 70%, of which 88% was comprised by shrubs and trees (Table 1). Bare soil and open water covered almost 30%. Native plants covered 34% of the floodplain, while exotic plants covered 37%. Cottonwoods and willows covered 8% of the floodplain (Table 2). Other trees present in the floodplain were honey mesquite (Prosopis glandulosa) and screwbean mesquite (Prosopis pubescens), but in lower numbers (Table 2). Saltcedar was the most common shrub, followed by arroweed (Pluchea sericea), seep willow (Baccharis spp.), and saltbush (Table 3). Cattail (Typha domengensis) was the dominant emergent species, but common reed (Phragmytes australis) and bulrush (Scirpus spp.) were also present

(Table 4).

129

Cottonwood and willow trees had a higher total coverage in the area between the

Railroad Bridge and Vado Carranza (Table 5, Figure 2). However the tree strata had a higher coverage on the left margin south of Vado Carranza, mostly dominated by saltcedar (Table 5 and 6). The survey sites with higher coverage of bare soil were scattered throughout the floodplain, but were mostly located between San Luis and the railroad bridge on the left margin (Table 6). The area of the railroad bridge had the highest coverage of emergent vegetation, followed by the sites close to Ayala Drain (31 and 32; Table 6). Seven transects had no open water (Table 6). These were mostly located on the right margin closer to the Hardy River. Of the rest, 14 transects had a water coverage >5%.

AVIAN COMMUNITIES

The floodplain of the Colorado River in Mexico supported an abundant and diverse avifauna. We obtained a total of 109 287 bird records from 186 species from May 2002 to July 2003 (Table 7). The average abundance per point was 29.2 individuals (± 1.2) with an average richness of 8.6 species (± 0.2, Table 8), and an average density of 47.7 birds per ha (± 7.0). Overall, the most common species were Mourning Doves, Red- winged Blackbirds, and Brown-headed Cowbirds (Table 9), which together comprise

41% of all records. However, 64 species were commonly found (>10 records per visit), including Verdins, Cliff Swallows, Song Sparrows, and Abert’s Towhees (Table 9).

There were 38 species with <5 total records, some of which were accidental or vagrant birds in the area (Zone-tailed Hawk, White-breasted Nuthatch, Gray Vireo, Red-

130 shouldered Hawk), while others were formerly common and now have become rare

(Lucy’s Warbler, Bell’s Vireo, and Brown-Crested Flycatcher).

Abundance was higher during the winter months (F3,446 = 10.05, P < 0.001,

Turkey-Kramer pairwise comparisons among seasons P < 0.001, Table 8, Figure 4).

Changes in abundance of Red-winged Blackbirds in the floodplain account for up to 65%

of the differences in abundances between seasons, as they increase from an estimate of 88

2 500 individuals (95% C.I. 29 480 – 265 780, 467 observations, χ 480 = 0.52) in summer

(July-August), to 1 473 000 individuals (95% C.I. 728 285 – 2 979 750, 5815

2 observations; χ 89 = 0.48) in winter (December-January), when they were the most

common species detected. Beside the common resident birds that maintain their numbers

in the area, the floodplain receives the influx of wintering residents, such as Ruby-

Crowned Kinglets, Yellow-Rumped Warblers, and Blue-Gray Gnatcatchers, which contribute to the higher abundance during this season.

The average species richness by transect was higher during spring (April-June,

F3,446 = 8.89, P <0.001, Turkey-Kramer pairwise comparisons among seasons P < 0.02;

Table 8, Figure 4). This pattern corresponds to the temporary presence of 64 species of neotropical migratory birds visiting the floodplain as a stopover site on their way north, being most common Northern Rough-winged Swallows, Wilson’s Warbler, Warbling

Vireo, Willow Flycatcher, Pacific-slope Flycatcher, Yellow Warbler, Townsend’s

Warbler and Western Tanager. The pattern is also influenced by the initial detections in the year of 14 species of breeding residents, arriving from their wintering grounds.

131

During summer, the avifauna in the floodplain is limited to the resident species and breeding seasonal visitors. The breeding community of birds in the area was composed of 61 species (4 non-native), including riparian generalists (White-winged

Dove, Blue Grosbeak, Western Kingbird, Ash-throated Flycatcher, and Ladder-backed

Woodpecker), riparian specialists (Yellow-billed Cuckoo, Vermillion Flycatcher, and

Yellow-breasted Chat), marsh breeders (Clapper Rail, Least Bittern, and Marsh Wren), raptors (Barn Owl, Osprey, and White-tailed Kite), and waterbirds (Cinnamon Teal,

Snowy Egret, and Black-necked Stilt).

Brown-headed Cowbirds are resident in the Colorado River delta/Mexicali Valley area. However, they have regional movements, almost disappearing from the riparian areas in late fall and winter (i.e. no records in November and 4 records in December).

Then they drastically increase their numbers during summer, with an estimate of 105 400

2 individuals in the floodplain (95% C.I. 84 400 – 131 700, 757 observations, χ 370 = 0.35).

The indices are lower in the fall, as most of the breeding residents start their

southbound migration, and the influx of transient birds is not as high as during the spring.

The geographic distribution of bird densities and species richness in the

floodplain followed similar patterns (Figure 5 and 6). Both are high in the wide plain near

San Luis, where surface water is almost perennial due to drainage and discharges from

the irrigation canals. In the thin stretch between San Luis and the railroad bridge, there

are some spots where density and richness are high, but those patches are relatively small,

and follow a narrow pattern around the main channel of the river. Between the Railroad

Bridge and Vado Carranza, the floodplain widens, has a softer slope, and contains large

132 stands of cottonwoods and willows. Here, bird densities and species richness are increased. Below Vado Carranza, both parameters tend to decrease, especially on the northwestern section of the floodplain, which consists primarily of elevated terraces dominated by saltcedar. However, there are some areas in the southwestern portion of this section that have high values of bird densities and species richness, basically the areas influenced by the main channel, some secondary streams, and agricultural drains.

HABITAT RELATIONSHIPS

The variability in species richness in the floodplain was explained mostly by variations in cover (ha) of surface water (r2 = 0.47, P < 0.001, Table 10 and 11). When analyzing the

relationship through the seasons, the importance of surface water was consistent, but other variables were also significant, particularly during summer, when average species richness was explained by variations in water (P < 0.001) and the cover of cottonwoods

(P = 0.02; overall model r2 = 0.56 and P < 0.001, Table 10 and 11), both habitat features

with strong positive relationships with species richness.

The variability in bird densities in the floodplain was explained mostly by variations in cover of surface water and screwbean mesquite (r2 = 0.32, P = 0.005), both

habitat features with a positive relationship to avian densities. The relationship was

similar during spring, fall, and winter. During summer, surface water was still important in explaining variation in bird densities (P = 0.02), but the other important habitat feature,

also with a positive relationship, was the percent cover of willows (P = 0.006, overall model r2 = 0.35 and P = 0.003).

133

DISCUSSION

The flows that have reached the floodplain of the Colorado River in Mexico in the last 25 years have regenerated limited but important stands of native riparian vegetation, despite the previous dominance of saltcedar (Zamora-Arroyo et al. 2001, Nagler et al. 2005). Our results suggest that the bird community has responded accordingly. Assuming that our estimates of avian indices and those from the Lower Colorado in the U.S. (Anderson et al. 1983) are comparable and unbiased, we calculate that bird densities are one order of magnitude higher in the Colorado River in Mexico than in the U.S. and that species richness values are similar.

Even though the influence of the adjacent agricultural areas and the long-lasting degradation are evident in the Colorado River in Mexico, the floodplain maintains large populations of many species of riparian birds, many of which are protected species or are targets of continental or regional bird conservation plans (Hinojosa-Huerta et al. 2004).

The floodplain also functions as an important connection in the migration of neotropical migratory landbirds and some waterbirds. During spring, the floodplain connects the migration route that extends north following the coast of the Gulf of

California with the corridor of the whole Colorado River, also serving as a stopover area for birds that migrate through coastal and central California (Ecton 2003).

Species that were considered extirpated in this region, such as Yellow-billed

Cuckoo, Vermillion Flycatcher, Osprey, and Clapper Rail (Ruiz-Campos and Rodriguez

–Meraz 1997, Patten et al. 2001) were found to be commonly breeding in the floodplain

134 during our study. Although no controlled bird surveys were performed before and after the regeneration events, the historic information on vegetation dynamics in the area during the last 25 years (Glenn et al. 1996, Glenn et al. 2001, Zamora-Arroyo et al. 2001) suggests that habitat for these species disappeared from the floodplain, and that these birds returned as breeders after the regeneration of the riparian ecosystem vegetative communities.

However, not all potential breeding species have returned to the floodplain. In some cases, this could be attributed to factors related to the overall status of the population, and not to the lack of appropriate habitat features in the area, as might be the case of the Southwestern Willow Flycatcher. The floodplain appears to have adequate vegetation features (young stands of willows and saltcedar with very dense mid and understory, near shallow water areas) for breeding Southwestern Willow Flycatchers

(Sogge et al. 1997), but the population may simply be too small to colonize recently restored areas.

In other cases, the lack of certain vegetation attributes might be precluding the colonization of some species. This might be the case of the Summer Tanager, Lucy’s

Warbler, Bell’s Vireo, Yellow Warbler, and Elf Owl, which require older and mature trees and/or cavities to nest. Although the floodplain maintains significant riparian forests, the estimated median age of cottonwoods and willows in the floodplain is 3 years, with a rapid turnover rate due to the prevalence of human-induced disturbance events, particularly logging, fire, and flood-prevention clear cuttings (Nagler et al. 2005). Thus, stands of older (>8 years old) trees are missing from the floodplain.

135

Water has been long recognized as the basis for riparian ecosystems. But it is not only valuable as a base flow to maintain the vegetation and as a pulse flood to maintain dynamics and enhance recruitment, but also as a land cover feature (surface water) that provides habitat for a variety of species and promotes primary productivity and insect biomass (Naiman et al. 2005). In our study, the presence of surface water was a significant predictor of both species richness and abundance, regardless of vegetation type or other land cover features. As expected, native trees had a positive association with the avian indices, particularly during the breeding season.

The relationship between cottonwood/willows and saltcedar in the floodplain in

Mexico appeared to be a function of the occurrence of flows and pulse floods, as the native trees were germinating, growing and seeding throughout the study area, particularly in the areas influenced by overbank flooding. Saltcedar was dominant in the upper, saltier, and drier terraces. Thus cottonwoods and willows survive and reproduce successfully when adequate water is present, even when saltcedar is common (Sher et al.

2000, Stromberg and Chew 2002, Nagler et al. 2005).

The areas dominated by cottonwoods and willows still had significant cover of saltcedar, but mostly as a mid- or understory species, adding structural diversity to a site.

Similar results were found in a Mojave Desert watershed, where bird diversity was not affected by the invasion of saltcedar, and the avian indices were best modeled by total vegetation volume and structural diversity (Fleishman et al. 2003).

Of major concern are the mesquite species, which only represent a small fraction of the vegetation cover in the floodplain, and yet, are important predictors of bird

136 densities. Probably the habitat of mesquite trees has been widely reduced, as it used to occupy elevated terraces, adjacent to the cottonwood-willow forests (Stromberg and

Chew 2002). These areas are now converted into agriculture, or otherwise have become too salty for mesquite and are dominated by sparse saltcedar shrubs.

In order to maintain the existing values in the Colorado River floodplain in

Mexico, several key strategies are required: 1) a base flow should be secured, in order to maintain the existing vegetation and optimize the cover of surface water, 2) pulse-flood events should be allocated to maintain dynamism and the regeneration of native trees, 3) human-induced disturbances (fires and logging) should be avoided or minimized in the floodplain, especially if they prevent the establishment of older stands of cottonwoods and willows, and 4) active manipulation may be needed to re-establish mesquite dominated terraces. Detailed estimations of the required base and pulse floods to maintain the health of the riparian corridor have been generated by Glenn et al. (2001).

Based on our results, the large-scale restoration of riparian areas and the associated bird populations is more a function of water management than of eradication of saltcedar and active plantings of cottonwood and willows. In fact, the restoration of a more natural hydrologic regime appears to control saltcedar effectively (Stromberg and

Chew 2002, Glenn and Nagler 2005, Nagler et al. 2005). However, certain species in some situations would require more active efforts, particularly the regeneration of mesquite bosque on elevated, stabilized terraces. Yet, more research is required to determine the large-scale effectiveness of a mesquite restoration effort and develop guidelines for implementation. The maintenance of existing vegetation cover and

137 structural diversity, and an increase in the amount of older riparian stands and mesquite bosque will secure the viability of existing bird populations and will increase the probability of recovery of the species that are still extirpated from the floodplain of the

Colorado River in Mexico.

ACKNOWLEDGEMENTS

Our special gratitude to Juan Butrón, José Juan Butrón, Mauricio Butrón, Jaqueline

García, Victor Ortega, Juan Rivera, Gerardo Sánchez, Pablo Valle, Michael Vamstad,

Alberto Zepeda and the numerous volunteers that helped during field activities. Our work has been possible thanks to the help of Sacha Heath, Chris McCreedy, Roy Churchwell and Steve Latta (Point Reyes Bird Observatory), Robert Mesta (Sonoran Joint Venture),

Yamilett Carrillo, Meredith de la Garza and Raquel Castro (Pronatura Sonora), Consejo

Nacional de Ciencia y Tecnología (CONACyT), the National Fish and Wildlife

Foundation and the Wallace Foundation. Comments from Courtney Conway, Kevin

Fitzsimmons, Edward Glenn, William Mannan and William Shaw provided insight for the analysis and discussion.

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Sons, New York, NY.

Sykes, G. 1937. The Colorado Delta. American Geographical Society Special Publication

19.

Thomas, L., Laake, J.L., Strindberg, S., Marques, F.F.C., Buckland, S.T., Borchers, D.L.,

Anderson, D.R., Burnham, K.P., Hedley, S.L., and Pollard, J.H. 2002. Distance 4.0.

Release 1. Research Unit for Wildlife Population Assessment, University of St.

Andrews, UK. http://www.ruwpa.st-and.ac.uk/distance/

143

Zamora-Arroyo, F., P.L. Nagler, M. Briggs, D. Radtke, H. Rodríguez, J. García, C.

Valdés, A. Huete, and E.P Glenn. 2001. Regeneration of native trees in response to

flood releases from the United States into the delta of the Colorado River, Mexico.

Journal of Arid Environments 49: 49-64.

Zamora-Arroyo, F., J. Pitt, S. Cornelius, E. Glenn, O. Hinojosa-Huerta, M. Moreno, J.

García, P. Nagler, M. de la Garza, I. Parra. 2005. Conservation Priorities in the

Colorado River Delta, Mexico and the United States. Prepared by the Sonoran

Institute, Environmental Defense, University of Arizona, Pronatura Noroeste

Dirección de Conservación Sonora, Centro de Investigación en Alimentación y

Desarrollo (CIAD) and World Wildlife Fund-Gulf of California Program. Tucson,

AZ.

144

Table 1. Average cover and height of vegetation strata in the floodplain of the Colorado

River, Mexico. Confidence intervals (95%) are shown in parenthesis. The value of water in the Average Height column represents depth.

Strata Avg. Cover (%) Avg. Height (m) Trees 27.55 (24.82 - 30.28) 4.63 (4.45 - 4.85) Shrubs 35.04 (32.35 - 37.72) 1.72 (1.68 - 1.76) Emergent 5.40 (4.32 - 6.49) 2.06 (1.94 - 2.18) Herbs 1.93 (1.43 - 2.43) 0.39 (0.31 - 0.47) Forbs 0.52 (0.16 - 0.87) 0.12 (0.09 - 0.154) Water 5.65 (4.59 - 6.71) 0.34 (0.28 – 0.39) Bare Soil 23.89 (21.46 - 26.32) -

Table 2. Average cover and height of plant species within the tree stratum in the

floodplain of the Colorado River, Mexico. Confidence intervals (95%) are shown in

parenthesis.

Tree Species Avg. Cover (%) Avg. Height (m) Willow 5.52 (4.23 - 6.81) 4.89 (4.49 - 5.14) Cottonwood 1.66 (1.16 - 2.17) 6.01 (5.39 - 6.62) Honey Mesquite 0.29 (-0.10 - 0.70) 3.81 (3.36 - 4.25) Screwbean Mesquite 0.74 (0.29 - 1.19) 3.63 (3.37 - 3.89) Saltcedar 19.36 (16.82 - 21.90) 3.50 (3.35 - 3.66)

145

Table 3. Average cover and height of plant species within the shrub stratum in the floodplain of the Colorado River, Mexico. Confidence intervals (95%) are shown in parenthesis.

Shrub species Avg. Cover (%) Avg. Height (m) Saltcedar 15.37 (13.18 - 17.56) 1.89 (1.80 - 1.98) Saltbush 1.30 (0.41 - 2.18) 1.34 (1.19 - 1.50) Screwbean Mesquite 0.07 (0 - 0.15) 1.88 (1.11 - 2.63) Cottonwood 0.03 (-0.01 - 0.08) 1.87 (0.68 - 3.06) Willow 0.63 (0.34 - 0.92) 2.15 (1.96 - 2.35) Arroweed 11.23 (9.12 - 13.34) 1.43 (1.35 - 1.51) Seep Willow 4.80 (3.60 - 5.99) 1.72 (1.63 - 1.81)

Table 4. Average cover and height of plant species within the emergent stratum in the floodplain of the Colorado River, Mexico. Confidence intervals (95%) are shown in

parenthesis.

Emergent species Avg. Cover (%) Avg. Height (m) Cattail 2.11 (1.45 - 2.76) 2.03 (1.89 - 2.18) Bulrush 0.42 (0.23 - 0.61) 1.14 (0.99 - 1.29) Common Reed 1.97 (1.19 - 2.75) 2.3 (2.14 - 2.46)

146

Table 5. Average tree cover by transect in the floodplain of the Colorado River, Mexico.

COTT: Cottonwood, WILL: Willow, SALT: Saltcedar, SCME: Screwbean Mesquite,

HOME: Honey Mesquite.

Transect COTT WILL SALT SCME HOME COTT+WILL 1 5.9583 16.218818.2500 4.6250 0.0000 22.1771 2 0.0000 13.678631.1563 0.0000 0.0000 13.6786 3 0.0000 27.308624.5200 0.0000 0.2400 27.3086 4 1.8333 1.8500 10.0625 0.7500 0.8750 3.6833 5 0.7500 5.0833 8.0000 0.0000 0.0000 5.8333 6 0.5000 5.5000 19.1786 1.5000 0.2500 6.0000 7 12.0000 6.7500 30.0000 20.33330.0000 18.7500 8 8.7375 7.8429 17.3357 6.4000 3.9250 16.5804 9 5.8100 3.7400 29.5417 0.0000 0.0000 9.5500 10 0.0000 5.0000 7.5000 0.0000 0.0000 5.0000 11 0.2500 0.0000 11.9500 0.0000 0.0000 0.2500 12 0.0000 5.1875 6.0000 0.6250 0.0000 5.1875 13 0.0000 8.1200 27.6750 8.0000 0.0000 8.1200 14 1.2000 9.4250 30.6625 6.4900 4.0333 10.6250 15 0.0000 0.0000 20.0000 6.0000 0.0000 0.0000 16 6.0000 1.0000 14.6667 6.0000 0.0000 7.0000 17 3.1800 18.200024.7625 0.0000 0.0000 21.3800 18 0.0000 4.3750 9.4063 0.0000 1.0000 4.3750 19 1.0000 2.1875 6.2500 0.0000 0.0000 3.1875 20 4.6250 6.9643 17.1875 0.2500 0.0000 11.5893 21 1.9167 2.2857 23.3063 1.5000 0.0000 4.2024 22 6.1500 4.3333 24.0875 2.0000 0.0000 10.4833 23 27.0000 10.833319.1429 2.0000 0.0000 37.8333 24 9.6667 19.800014.5000 0.7500 0.0000 29.4667 25 8.4600 21.375013.3000 0.0000 0.2000 29.8350 26 5.7857 8.9286 13.8571 0.0000 0.0000 14.7143 27 3.6333 5.7333 46.6750 2.4000 49.5000 9.3667 28 3.0000 4.2800 48.1313 0.0000 0.5500 7.2800 29 0.0000 4.2500 52.4875 0.0000 0.2833 4.2500 30 0.0000 0.0000 33.1250 0.0000 0.0000 0.0000

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Table 6. Average strata coverage by transect in the floodplain of the Colorado River,

Mexico.

Transect Emergent Trees Shrubs Herbs Forbs Bare Soil Water 1 0.0000 41.2500 43.7500 0.0000 0.000010.6250 4.3750 2 1.8750 43.1250 26.2500 1.2500 0.000027.5000 0.0000 3 7.5000 39.2500 33.7500 0.1250 0.000015.0000 4.3750 4 6.8750 12.5000 55.0000 0.0000 0.000022.2500 3.3750 5 9.3750 10.0000 31.8750 5.6250 0.000031.8750 11.2500 6 10.6250 20.0000 22.5000 2.5000 0.875030.3750 13.1250 7 3.1250 42.5000 32.5000 0.6250 0.000019.3750 1.8750 8 4.8750 40.0000 35.0000 1.2500 0.125014.3750 4.3750 9 0.0000 28.1250 63.1250 0.0000 0.00005.6250 3.1250 10 0.0000 2.5000 40.0000 0.6250 0.000056.8750 0.0000 11 0.0000 7.5000 59.3750 0.0000 0.000033.1250 0.0000 12 0.0000 5.0000 63.7500 0.0000 0.000031.2500 0.0000 13 0.7500 33.7500 23.5000 4.3750 0.000032.5000 5.1250 14 2.6250 43.7500 23.1250 1.2500 0.000025.5000 3.7500 15 0.0000 18.2500 13.7500 3.6250 0.000064.3750 0.0000 16 1.8750 13.7500 20.0000 6.8750 5.625043.1250 8.7500 17 1.2500 38.1250 50.6250 0.0000 0.00007.5000 2.5000 18 0.0000 10.6250 40.0000 3.1250 0.000046.2500 0.0000 19 15.0000 8.1250 23.1250 7.5000 0.000020.6250 25.6250 20 1.2500 25.6250 46.8750 0.0000 0.000018.1250 8.1250 21 15.0000 26.2500 37.5000 1.2500 0.000010.6250 9.3750 22 18.7500 27.5000 20.0000 0.6250 0.000020.0000 13.1250 23 11.2500 21.8750 40.0000 0.0000 0.000021.8750 5.0000 24 9.3750 32.5000 28.1250 3.1250 0.750016.1250 10.0000 25 7.5000 35.0000 37.5000 5.0000 0.00009.3750 5.6250 26 10.6250 25.0000 37.5000 6.2500 0.6250 5.6250 14.3750 27 0.0000 59.1250 30.2500 0.0000 0.00005.7500 4.8750 28 3.7500 51.2500 21.8750 0.0000 0.000019.3750 3.7500 29 6.2500 53.1250 35.6250 0.0000 0.00005.0000 0.0000 30 13.1250 33.1250 26.8750 0.0000 0.000024.3750 2.5000

148

Table 7. Bird species detected during 2002 and 2003 in the floodplain of the Colorado River, Mexico. Taxonomic nomenclature and order follow the American Ornithologists’ Union (AOU 1998, Banks et al. 2004). Four-letter codes follow Pyle (1997).

Common Name Scientific Name Four-letter Code Greater White-fronted Goose Anser albifrons GWFG Snow Goose Chen caerulescens SNGO Canada Goose Branta canadensis CAGO Gadwall Anas strepara GADW American Wigeon Anas americana AMWI Mallard Anas platyrhynchos MALL Blue-winged Teal Anas discors BWTE Cinnamon Teal Anas cyanoptera CITE Northern Shoveler Anas clypeata NSHO Northern Pintail Anas acuta NOPI Green-winged Teal Anas crecca GWTE Canvasback Aythya valisineria CANV Redhead Aythya americana REDH Ring-necked Duck Aythya collaris RNDU Lesser Scaup Aythya affinis LESC Bufflehead Bucephala albeola BUFF Common Merganser Mergus merganser COME Red-breasted Merganser Mergus serrator RBME Ruddy Duck Oxyura jamaicensis RUDU Gambel's Quail Callipepla gambelii GAQU Pied-billed Grebe Podilymbus podiceps PBGR Eared Grebe Podiceps nigricollis EAGR American White Pelican Pelecanus erythrorhynchos AWPE Brown Pelican Pelecanus occidentalis BRPE Double-crested Cormorant Phalacrocorax auritus DCCO American Bittern Botaurus lentiginosus AMBI Least Bittern Ixobrychus exilis LEBI Great Blue Heron Ardea herodias GBHE Great Egret Ardea alba GREG Snowy Egret Egretta thula SNEG Tricolored Heron Egretta tricolor TRHE Reddish Egret Egretta rufescens REEG Cattle Egret Bubulcus ibis CAEG Green Heron Butorides virescens GRHE Black-crowned Night-Heron Nycticorax nycticorax BCNH White-faced Ibis Plegadis chihi WFIB Wood Stork Mycteria americana WOST Black Vulture Coragyps atratus BLVU Turkey Vulture Cathartes aura TUVU

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Osprey Pandion haliaetus OSPR White-tailed Kite Elanus leucurus WTKI Northern Harrier Circus cyaneus NOHA Sharp-shinned Hawk Accipiter striatus SSHA Cooper's Hawk Accipiter cooperii COHA Red-shouldered Hawk Buteo lineatus RSHA Swainson's Hawk Buteo swainsoni SWHA Zone-tailed Hawk Buteo albonotatus ZTHA Red-tailed Hawk Buteo jamaicensis RTHA Ferruginous Hawk Buteo regalis FEHA American Kestrel Falco sparverius AMKE Merlin Falco columbarius MERL Peregrine Falcon Falco peregrinus PEFA Prairie Falcon Falco mexicanus PRFA Yuma Clapper Rail Rallus longirostris CLRA Virginia Rail Rallus limicola VIRA Sora Porzana carolina SORA Common Moorhen Gallinula chloropus COMO American Coot Fulica americana AMCO Black-bellied Plover Pluvialis squatarola BBPL Semipalmated Plover Charadrius semipalmatus SEPL Killdeer Charadrius vociferus KILL Black-necked Stilt Himantopus mexicanus BNST American Avocet Recurvirostra americana AMAV Greater Yellowlegs Tringa melanoleuca GRYE Lesser Yellowlegs Tringa flavipes LEYE Solitary Sandpiper Tringa solitaria SOSA Willet Catotrophorus semipalmatus WILL Spotted Sandpiper Actitis macularia SPSA Whimbrel Numenius phaeopus WHIM Long-billed Curlew Numenius americanus LBCU Marbled Godwit Limosa fedoa MAGO Black Turnstone Arenaria melanocephala BLTU Sanderling Calidris alba SAND Western Sandpiper Calidris mauri WESA Least Sandpiper Calidris minutilla LESA Dunlin Calidris alpina DUNL Short-billed Dowitcher Limnodromus griseus SBDO Long-billed Dowitcher Limnodromus scolopaceus LBDO Wilson's Snipe Gallinago delicata WISN Laughing Gull Larus atricilla LAGU Franklin's Gull Larus pipixcan FRGU Bonaparte's Gull Larus philadelphia BOGU Ring-billed Gull Larus delawarensis RBGU California Gull Larus californicus CAGU Western Gull Larus occidentalis WEGU

150

Gull-billed Tern Sterna nilotica GBTE Caspian Tern Sterna caspia CATE Forster's Tern Sterna forsteri FOTE Least Tern Sterna antillarum LETE Black Tern Chlidonias niger BLTE Black Skimmer Rhynchops niger BLSK White-winged Dove Zenaida asiatica WWDO Mourning Dove Zenaida macroura MODO Inca Dove Columbina inca INDO Common Ground-Dove Columbina passerina COGD Yellow-billed Cuckoo Coccyzus americanus YBCU Greater Roadrunner Geococcyx californianus GRRO Barn Owl Tyto alba BNOW Great Horned Owl Bubo virginianus GHOW Burrowing Owl Athene cunicularia BUOW Lesser Nighthawk Chordeiles acutipennis LENI Vaux's Swift Chaetura vauxi VASW White-throated Swift Aeronautes saxatalis WTSW Black-chinned Hummingbird Archilochus alexandri BCHU Anna's Hummingbird Calypte anna ANHU Costa's Hummingbird Calypte costae COHU Allen's Hummingbird Selasphorus sasin ALHU Belted Kingfisher Ceryle alcyon BEKI Gila Woodpecker Melanerpes uropygialis GIWO Red-naped Sapsucker Sphyrapicus nuchalis RNSA Ladder-backed Woodpecker Picoides scalaris LBWO Northern Flicker Colaptes auratus NOFL Western Wood-Pewee Contopus sordidulus WEWP Willow Flycatcher Empidonax traillii WIFL Pacific-slope Flycatcher Empidonax difficilis PSFL Black Phoebe Sayornis nigricans BLPH Say's Phoebe Sayornis saya SAPH Vermilion Flycatcher Pyrocephalus rubinus VEFL Ash-throated Flycatcher Myiarchus cinerascens ATFL Brown-crested Flycatcher Myiarchus tyrannulus BCFL Western Kingbird Tyrannus verticalis WEKI Loggerhead Shrike Lanius ludovicianus LOSH Bell's Vireo Vireo bellii BEVI Gray Vireo Vireo vicinior GRVI Warbling Vireo Vireo gilvus WAVI American Crow Corvus brachyrhychos AMCR Common Raven Corvus corax CORA Horned Lark Eremophila alpestris HOLA Tree Swallow Tachycineta bicolor TRES Violet-green Swallow Tachycineta thalassina VGSW Northern Rough-winged Swallow Stelgidopterx serripennis NRWS

151

Cliff Swallow Petrochelidion pyrrhonata CLSW Barn Swallow Hirundo rustica BARS Verdin Auriparus flaviceps VERD Cactus Wren Campylorhynchus brunneicapillus CACW Rock Wren Salpinctes obsoletus ROWR Bewick's Wren Thryomanes bewickii BEWR House Wren Troglodytes aedon HOWR Marsh Wren Cistothorus palustris MAWR Ruby-crowned Kinglet Regulus calendula RCKI Blue-gray Gnatcatcher Polioptila caerulea BGGN Black-tailed Gnatcatcher Polioptila melanura BTGN Swainson's Thrush Catharus ustulatus SWTH Hermit Thrush Catharus guttatus HETH American Robin Turdus migratorius AMRO Northern Mockingbird Mimus polyglottos NOMO Crissal Thrasher Toxostoma crissale CRTH American Pipit Anthus rubescens AMPI Phainopepla Phainopepla nitens PHAI Orange-crowned Warbler Vermivora celata OCWA Nashville Warbler Vermivora ruficapilla NAWA Lucy's Warbler Vermivora luciae LUWA Yellow Warbler Dendroica petechia YWAR Yellow-rumped Warbler Dendroica coronata YRWA Black-throated Gray Warbler Dendroica nigrescens BTYW Townsend's Warbler Dendroica townsendi TOWA Hermit Warbler Dendroica occidentalis HEWA MacGillivray's Warbler Oporornis tolmiei MGWA Common Yellowthroat Geothlypis trichas COYE Wilson's Warbler Wilsonia pusilla WIWA Yellow-breasted Chat Icteria virens YBCH Western Tanager Piranga ludoviciana WETA Green-tailed Towhee Pipilo chlorurus GTTO Spotted Towhee Pipilo maculatus SPTO Abert's Towhee Pipilo aberti ABTO Chipping Sparrow Spizella passerina CHSP Song Sparrow Melospiza melodia SOSP Lincoln's Sparrow Melospiza lincolnii LISP White-crowned Sparrow Zonotrichia leucophrys WCSP Dark-eyed Junco Junco hyemalis DEJU Black-headed Grosbeak Pheuticus melanocephalus BHGR Blue Grosbeak Guiraca caerulea BLGR Lazuli Bunting Passerina amoena LAZB Red-winged Blackbird Agelaius phoeniceus RWBL Western Meadowlark Sturnella neglecta WEME Yellow-headed Blackbird Xanthocephalus xanthocephalus YHBL Great-tailed Grackle Quiscalus mexicanus GTGR

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Brown-headed Cowbird Molothrus ater BHCO Hooded Oriole Icterus cucullatus HOOR Bullock's Oriole Icterus bullockii BUOR House Finch Carpodacus mexicanus HOFI Lesser Goldfinch Carduelis psaltria LEGO Ring-necked Pheasant Phasianus colchicus RNEP Rock Dove Columba livia RODO European Starling Sturnus vulgaris EUST House Sparrow Passer domesticus HOSP

Table 8. Bird abundance and species richness per visit, per point and per route in the floodplain of the Colorado River, Mexico, 2002-2003. Standard errors are shown in parentheses.

Avg. Avg. Avg. Avg. Total abund richness abund richness Visit Abundance Species per point per point per route per route Month 1 6782 112 26 (0.9) 10 (0.3) 204 (16) 30 (1.5) May 2 6044 85 23 (0.7) 10 (0.2) 182 (11) 27 (1.3) June 3 6171 76 23 (1.0) 9 (0.2) 187 (16) 23 (1.2) July 4 4256 83 17 (0.9) 6 (0.2) 133 (13) 19 (1.5) Aug 5 6520 108 24 (1.8) 8 (0.2) 192 (21) 26 (1.8) Septr 6 5912 112 24 (2.3) 7 (0.2) 189 (28) 24 (1.7) Oct 7 6357 95 25 (3.2) 6 (0.2) 203 (34) 21 (1.4) Nov 8 7376 104 26 (3.9) 7 (0.3) 211 (41) 24 (1.9) Decr 9 11 076 108 46 (8.6) 7 (0.3) 369 (86) 26 (1.8) Jan 10 7506 100 31 (3.3) 7 (0.3) 250 (44) 23 (1.9) Feb 11 10 921 104 45 (4.5) 8 (0.3) 364 (65) 26 (2.0) March 12 7799 116 32 (1.4) 11 (0.2) 260 (23) 31 (1.7) April 13 7180 83 30 (1.3) 11 (0.2) 239 (17) 28 (1.1) May 14 7242 78 30 (1.2) 11 (0.2) 241 (16) 28 (1.1) June 15 8145 76 35 (2.0) 10 (0.2) 281 (24) 27 (1.4) July Total. 109 287 186 29 (1.2) 9 (0.2) 234 (19) 25 (1.3)

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Table 9. Total detections by visit and relative dominance of all species detected in the

Colorado River, Mexico 2002-2003. Four-letter codes for species are given in Table 8.

Visits started in May 2002 (V1) and continued monthly until July 2003 (V15).

Bird V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 Total Rel Dom MODO 1163 1033 1214 1360 1482 1059 1828 1185 907 1426 1911 1377 1366 1419 1543 20273 18.6466 RWBL 763 618 390 77 711 1161 1496 1275 4539 1844 2784 829 749 923 1123 19282 17.7351 BHCO 757 557 624 81 729 67 0 4 136 6 141 726 595 571 485 5479 5.0395 VERD 290 269 304 181 342 258 155 214 344 325 441 481 459 366 325 4754 4.3726 CLSW 309 320 552 113 38 0 0 0 0 35 659 295 372 229 1288 4210 3.8723 GTGR 245 144 226 89 27 288 259 256 506 393 585 248 135 310 219 3930 3.6147 SOSP 355 247 181 82 129 105 100 156 260 299 368 352 389 238 184 3445 3.1686 ABTO 121 163 164 73 301 228 129 154 192 163 179 262 316 430 392 3267 3.0049 GAQU 193 261 191 77 114 94 54 36 108 84 148 251 283 279 234 2407 2.2139 WWDO 94 161 207 254 13 1 0 0 0 0 0 154 341 226 263 1714 1.5765 BNST 205 256 374 206 79 60 53 26 31 46 55 68 65 67 83 1674 1.5397 COYE 86 151 172 25 51 78 79 94 77 99 106 145 213 142 156 1674 1.5397 YRWA 8 0 0 0 0 191 200 272 354 214 276 3 0 0 0 1518 1.3962 WEKI 213 160 248 40 48 4 1 0 0 0 1 208 162 192 207 1484 1.3649 DCCO 57 44 21 4 76 92 123 191 606 65 66 20 12 6 13 1396 1.2840 MAWR 25 39 21 36 71 70 92 92 138 164 152 118 123 75 57 1273 1.1709 KILL 136 127 112 109 139 38 10 18 30 50 83 106 100 84 67 1209 1.1120 RNEP 156 152 47 1 22 31 13 10 35 61 113 170 184 146 41 1182 1.0872 AMCO 13 6 14 1 23 81 139 291 194 190 144 32 17 24 9 1178 1.0835 RBGU 45 4 0 7 2 6 178 628 93 86 39 72 1 0 0 1161 1.0679 SNEG 100 144 126 109 131 26 45 90 24 12 18 90 80 95 58 1148 1.0559 WFIB 18 60 14 23 95 205 22 74 6 268 307 52 0 0 0 1144 1.0522 YHBL 35 43 67 25 176 21 40 0 265 41 223 9 18 18 43 1024 0.9419 NRWS 52 138 24 175 23 80 1 0 5 67 157 90 71 77 34 994 0.9143 BLGR 68 74 110 132 34 0 0 0 0 0 0 87 120 139 214 978 0.8995 AMWI 0 0 0 0 0 53 29 361 156 129 215 0 0 0 0 943 0.8673 BTGN 90 55 45 22 136 51 17 59 29 57 32 53 96 95 91 928 0.8536 MALL 16 9 0 6 18 17 77 238 122 227 88 13 5 1 0 837 0.7699 BLPH 18 17 21 43 100 106 101 122 94 54 13 16 32 27 24 788 0.7248 CACW 72 45 48 21 26 31 4 15 45 48 60 68 69 88 66 706 0.6494 GREG 46 49 25 40 53 63 38 17 25 16 32 58 40 64 122 688 0.6328 TUVU 25 27 34 114 100 122 69 41 8 8 28 9 18 22 26 651 0.5988 LBWO 7 20 14 9 65 39 31 63 47 45 72 39 53 63 57 624 0.5739 ATFL 19 46 55 24 36 20 16 20 26 37 41 69 62 58 56 585 0.5381 COMO 6 17 8 19 33 22 24 45 22 76 48 53 60 67 74 574 0.5280 TRES 22 0 0 58 26 3 1 0 69 38 131 99 78 28 3 556 0.5114 CITE 39 22 68 2 30 0 0 16 68 83 142 19 28 20 0 537 0.4939 HOSP 13 14 8 0 0 4 0 14 200 171 60 10 16 6 7 523 0.4810

154

AWPE 32 5 4 19 109 0 147 152 49 0 0 0 1 0 0 518 0.4764 EUST 0 12 0 0 19 51 76 51 40 5 7 27 15 181 8 492 0.4525 WESA 53 0 0 93 35 0 15 54 17 24 28 130 0 0 26 475 0.4369 LENI 63 45 42 39 3 0 0 0 0 0 0 46 68 57 84 447 0.4111 CRTH 5 13 14 5 44 30 19 24 37 39 37 25 24 28 41 385 0.3541 BCNH 17 27 38 34 45 26 7 13 61 4 8 22 21 32 28 383 0.3523 GBHE 28 31 16 28 41 33 29 40 33 13 20 13 8 14 23 370 0.3403 CATE 37 47 25 38 35 32 22 20 10 6 3 36 22 13 23 369 0.3394 OSPR 8 3 11 11 39 60 62 47 46 27 20 12 2 1 4 353 0.3247 WEME 16 20 24 1 18 22 13 22 25 32 19 19 29 33 17 310 0.2851 LBCU 1 0 0 5 27 14 0 68 49 0 129 0 0 0 7 300 0.2759 WHIM 26 0 0 52 13 31 35 0 0 8 90 8 0 0 33 296 0.2723 WCSP 7 0 0 0 0 85 61 65 60 11 5 0 0 0 0 294 0.2704 GWTE 0 0 0 0 0 0 0 4 168 64 46 0 0 0 0 282 0.2594 RCKI 1 0 0 0 1 39 28 65 64 30 35 3 0 0 0 266 0.2447 SBDO 19 0 0 32 16 14 0 27 3 15 17 116 0 0 0 259 0.2382 LESA 34 0 4 46 21 21 31 19 19 0 19 39 0 0 0 253 0.2327 GRYE 5 3 12 16 49 99 16 12 8 3 5 3 1 8 11 251 0.2309 HOOR 42 28 25 1 0 0 0 0 0 0 0 42 42 35 34 249 0.2290 CAEG 4 4 12 35 78 15 15 22 21 0 14 1 0 11 7 239 0.2198 BGGN 1 1 0 1 6 44 32 41 31 41 29 2 0 0 1 230 0.2115 GRHE 25 24 30 17 26 0 0 2 1 2 3 16 20 23 21 210 0.1932 SAND 0 0 0 10 0 59 58 5 42 0 19 5 0 0 0 198 0.1821 BARS 14 2 1 0 83 43 0 0 0 1 19 9 1 0 0 173 0.1591 COGD 16 6 8 7 15 13 2 2 12 3 7 17 27 14 20 169 0.1554 NOMO 17 24 36 3 11 7 1 4 13 2 2 7 20 8 6 161 0.1481 WILL 4 0 0 1 9 56 44 8 24 0 0 2 0 0 0 148 0.1361 CAGU 0 0 0 0 0 0 0 90 2 1 41 11 0 0 0 145 0.1334 YBCH 0 9 12 1 2 0 0 0 0 0 0 16 25 51 25 141 0.1297 WIWA 50 0 0 0 19 2 0 0 0 1 4 59 2 0 0 137 0.1260 LESC 0 0 0 0 0 3 6 22 96 1 8 0 0 0 0 136 0.1251 NOHA 2 0 0 0 10 24 21 28 16 23 9 1 0 2 0 136 0.1251 NOPI 0 0 0 0 8 17 0 6 35 28 35 0 0 0 0 129 0.1187 BUOR 7 27 15 1 0 0 0 0 0 0 0 31 18 12 16 127 0.1168 WIFL 0 91 0 0 0 0 0 0 0 0 0 0 12 0 0 103 0.0947 RODO 6 12 24 4 12 3 2 6 0 2 14 2 1 9 2 99 0.0911 NSHO 0 0 0 0 0 3 0 35 22 2 34 2 0 0 0 98 0.0901 WAVI 57 0 0 0 10 2 4 0 0 0 0 15 1 0 0 89 0.0819 SPSA 10 0 0 3 5 5 2 5 1 5 3 47 1 0 1 88 0.0809 GBTE 40 4 1 13 0 1 0 0 0 0 18 4 3 0 1 85 0.0782 LBDO 5 0 0 12 3 5 16 14 2 0 1 26 0 0 0 84 0.0773 BUOW 6 13 9 10 5 5 0 0 0 0 1 3 5 8 15 80 0.0736 GIWO 5 8 11 1 12 5 1 2 1 5 3 6 9 8 3 80 0.0736 LEYE 2 1 7 10 15 12 1 18 3 0 8 1 0 2 0 80 0.0736 AMCR 1 0 0 0 0 35 2 0 30 0 0 0 1 7 1 77 0.0708 CORA 5 5 3 1 6 8 8 3 10 6 0 5 2 5 6 73 0.0671 PBGR 4 4 3 0 2 0 3 4 4 6 18 7 2 7 9 73 0.0671

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AMKE 0 1 3 7 16 11 7 9 3 1 1 0 1 4 8 72 0.0662 VEFL 4 21 3 5 4 0 1 2 1 5 7 3 8 5 3 72 0.0662 PSFL 32 14 1 0 11 1 0 0 0 0 0 9 2 0 0 70 0.0644 RTHA 1 0 0 2 2 16 9 12 12 4 4 0 0 3 0 65 0.0598 FOTE 6 3 2 16 4 0 0 0 0 0 0 22 3 0 7 63 0.0579 LEBI 0 1 0 7 9 1 0 0 0 1 1 4 10 16 11 61 0.0561 BWTE 2 0 1 0 0 0 0 8 16 15 4 5 0 0 9 60 0.0552 GRRO 1 2 0 0 8 5 2 2 2 0 4 1 10 9 13 59 0.0543 BEKI 0 0 0 0 18 9 7 11 2 1 2 3 0 1 0 54 0.0497 LOSH 0 1 3 5 9 2 2 7 4 2 1 0 1 3 13 53 0.0487 SAPH 0 0 0 0 1 6 8 10 13 3 3 6 0 0 0 50 0.0460 CANV 0 0 0 0 0 0 0 35 14 0 0 0 0 0 0 49 0.0451 VGSW 20 2 0 1 22 0 0 2 0 1 1 0 0 0 0 49 0.0451 OCWA 9 0 0 0 2 2 4 1 7 11 4 8 0 0 0 48 0.0441 YWAR 21 1 4 0 4 0 0 0 0 0 0 10 8 0 0 48 0.0441 SORA 0 0 0 0 0 2 8 12 6 6 8 3 0 0 0 45 0.0414 WTKI 2 6 1 0 4 4 3 3 3 2 4 1 2 6 4 45 0.0414 CLRA 3 6 0 5 0 3 3 0 0 1 0 7 4 5 4 41 0.0377 CHSP 0 0 0 0 0 27 0 0 0 0 13 0 0 0 0 40 0.0368 AMAV 4 0 0 0 0 0 0 3 3 7 12 5 0 0 0 34 0.0313 INDO 1 2 6 8 0 1 0 0 0 8 0 1 4 1 0 32 0.0294 TOWA 21 0 1 0 0 0 0 0 0 0 0 8 0 0 0 30 0.0276 BRPE 0 1 19 3 6 0 0 0 0 0 0 0 0 0 0 29 0.0267 GADW 0 0 0 0 0 4 1 5 0 12 7 0 0 0 0 29 0.0267 NOFL 0 0 0 0 0 4 0 9 11 2 2 0 0 1 0 29 0.0267 AMPI 0 0 0 0 0 0 1 0 0 0 26 0 0 0 0 27 0.0248 COME 0 0 0 0 0 0 0 0 26 0 0 0 1 0 0 27 0.0248 HOWR 0 0 0 0 13 1 0 3 0 4 3 3 0 0 0 27 0.0248 DEJU 0 0 0 0 0 1 14 0 2 1 8 0 0 0 0 26 0.0239 DUNL 0 0 0 0 0 23 0 0 0 0 0 0 0 0 0 23 0.0212 HOFI 0 0 0 0 3 3 3 12 2 0 0 0 0 0 0 23 0.0212 BEWR 11 1 4 0 1 0 0 1 2 2 0 0 0 0 0 22 0.0202 WETA 19 0 0 0 0 0 0 0 0 0 0 2 0 0 0 21 0.0193 NAWA 4 0 0 0 0 0 0 0 1 0 0 14 0 0 0 19 0.0175 SWHA 0 0 0 0 10 0 1 6 0 0 0 0 0 0 0 17 0.0156 WOST 0 0 0 0 0 0 0 0 0 0 0 0 2 11 4 17 0.0156 PEFA 0 1 0 0 4 3 1 2 2 2 0 0 0 1 0 16 0.0147 SSHA 0 0 0 0 1 4 0 5 1 2 2 1 0 0 0 16 0.0147 REDH 0 0 0 0 0 0 0 2 4 9 0 0 0 0 0 15 0.0138 BUFF 0 0 0 0 0 0 0 0 0 14 0 0 0 0 0 14 0.0129 GWFG 0 0 0 0 0 0 0 0 14 0 0 0 0 0 0 14 0.0129 BOGU 0 0 0 0 0 0 0 0 0 0 0 0 0 0 13 13 0.0120 WEWP 5 2 0 0 0 0 0 0 0 0 0 2 4 0 0 13 0.0120 COHA 0 0 0 0 1 0 2 5 1 0 3 0 0 0 0 12 0.0110 HOLA 0 1 0 0 0 0 0 0 8 0 1 0 0 2 0 12 0.0110 AMRO 0 0 0 0 0 1 1 1 8 0 0 0 0 0 0 11 0.0101 BBPL 0 0 0 0 0 0 0 11 0 0 0 0 0 0 0 11 0.0101

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RUDU 0 0 0 0 0 6 0 0 0 2 3 0 0 0 0 11 0.0101 VASW 10 0 0 0 0 0 0 0 0 0 0 1 0 0 0 11 0.0101 BHGR 8 0 0 0 0 0 0 0 0 0 0 1 0 0 0 9 0.0083 EAGR 0 0 0 0 0 0 0 1 0 1 6 1 0 0 0 9 0.0083 RBME 0 0 0 0 0 0 0 0 1 8 0 0 0 0 0 9 0.0083 VIRA 0 0 0 0 2 1 1 1 1 1 0 2 0 0 0 9 0.0083 HEWA 7 0 0 0 0 0 0 0 0 0 0 1 0 0 0 8 0.0074 AMBI 1 0 1 0 1 0 0 0 1 0 0 2 1 0 0 7 0.0064 BLTE 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 7 0.0064 LEGO 0 0 0 0 0 0 0 1 0 0 0 0 2 0 4 7 0.0064 LISP 2 0 0 0 0 3 0 2 0 0 0 0 0 0 0 7 0.0064 SWTH 2 0 0 0 2 1 0 0 0 0 0 2 0 0 0 7 0.0064 BTYW 1 0 0 0 1 2 0 0 1 0 0 1 0 0 0 6 0.0055 CAGO 0 0 0 0 0 0 0 0 5 1 0 0 0 0 0 6 0.0055 WEGU 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 6 0.0055 WTSW 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 6 0.0055 BLSK 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 5 0.0046 BNOW 0 0 1 0 0 1 0 0 0 0 0 0 0 1 2 5 0.0046 COHU 1 1 1 0 0 1 0 0 0 0 0 0 1 0 0 5 0.0046 WISN 0 0 0 0 0 0 0 0 0 2 3 0 0 0 0 5 0.0046 MERL 0 0 0 0 3 0 1 0 1 0 0 0 0 0 0 5 0.0046 SPTO 0 0 0 0 4 1 0 0 0 0 0 0 0 0 0 5 0.0046 YBCU 0 0 0 0 3 0 0 0 0 0 0 0 0 0 2 5 0.0046 ANHU 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 4 0.0037 FEHA 0 0 0 0 0 0 1 0 2 0 1 0 0 0 0 4 0.0037 MAGO 3 0 0 1 0 0 0 0 0 0 0 0 0 0 0 4 0.0037 ROWR 0 0 0 0 0 3 1 0 0 0 0 0 0 0 0 4 0.0037 SNGO 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 4 0.0037 BEVI 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0.0028 HETH 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 3 0.0028 LAGU 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 3 0.0028 LAZB 2 0 0 0 0 0 0 0 0 0 0 1 0 0 0 3 0.0028 SEPL 2 0 0 0 0 0 0 0 0 0 0 1 0 0 0 3 0.0028 BCFL 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 2 0.0018 BCHU 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 2 0.0018 LUWA 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 2 0.0018 RNSA 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 2 0.0018 SOSA 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 2 0.0018 ZTHA 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 2 0.0018 ALHU 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0.0009 BLTU 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0.0009 FRGU 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0.0009 GHOW 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0.0009 GRVI 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0.0009 GTTO 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0.0009 LETE 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0.0009 MGWA 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0.0009

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PHAI 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0.0009 PRFA 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0.0009 REEG 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0.0009 RNDU 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0.0009 RSHA 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0.0009 TRHE 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0.0009

Table 10. Analysis of variance results of the multiple regression models of avian richness and density in the floodplain of the Colorado River in Mexico.

Model df F P r Adjusted r2 Bird Species Richness 1, 28 24.83 < 0.001 0.69 0.45 Bird Species Richness Summer 2, 27 17.4 < 0.001 0.75 0.53 Bird Density 2, 27 6.63 0.005 0.57 0.28 Bird Density Summer 2, 27 7.49 0.003 0.60 0.31

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Table 11. Effects and coefficient results of the multiple regression models of avian richness and density in the floodplain of the Colorado River in Mexico.

Response Std Std variable/Effect Coefficient Error Coef Tolerance t P Bird Species Richness Constant 20.74 1.34 0 . 15.49 < 0.001 Water 0.84 0.17 0.67 1.00 4.98 < 0.001

Bird Species Richness Summer Constant 19.89 1.07 0 . 18.55 < 0.001 Water 0.63 0.12 0.65 0.99 5.09 < 0.001 Cottonwoods 0.32 0.13 0.32 0.99 2.49 0.02

Bird Density Constant 22.50 9.38 0 . 2.40 0.02 Water 2.74 1.07 0.41 0.98 2.57 0.02 Screwbean Mesquites 4.21 1.45 0.46 0.98 2.90 0.01

Bird Density Summer Constant 9.75 7.50 0 . 1.30 0.20 Water 1.84 0.73 0.39 1.00 2.54 0.02 Willows 1.83 0.61 0.47 1.00 3.01 0.01

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Figure 1. Ecozones of the Colorado River delta, México. Agricultural areas include the

Mexicali and San Luis valleys. Off-channel wetlands refer to wetlands maintained by agricultural drainage discharge or seepage, and not directly connected with the active floodplain of the Colorado River.

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Figure 2. Sections of the floodplain in the Colorado River in México. The sections delimitate the extent of the native riparian vegetation in the area.

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Figure 3. Survey points for birds and vegetation in the floodplain of the Colorado River,

México.

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Figure 4. Average bird abundance and species richness per point by month in the floodplain of the Colorado River, Mexico, 2002-2003. Values for abundance are shown on the left y axis and values for richness are shown on the right y axis.

50 12 Avg. Abundance per point 45

Avg. richness per point 10 40

35 8

30

25 6

20

4 15

10 2

5

0 0 July July June June May May April March August January October February December November September

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Figure 5. Bird densities in the floodplain of the Colorado River, Mexico 2002-2003.

Values were estimated with 15 monthly surveys at 240 sites. The grid was interpolated using the Spatial Analyst extension of ArcView 3.2.

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Figure 6. Species richness in the floodplain of the Colorado River, Mexico 2002-2003.

Values were estimated with 15 monthly surveys at 240 sites. The grid was interpolated using the Spatial Analyst extension of ArcView 3.2.

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APPENDIX C

EFFECT OF VEGETATION TYPE AND SURFACE WATER ON RIPARIAN AVIAN

COMMUNITIES

Manuscript prepared for submission to the journal The Condor

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Effect of vegetation and water on riparian birds

EFFECT OF VEGETATION TYPE AND SURFACE WATER ON RIPARIAN AVIAN

COMMUNITIES

Osvel Hinojosa-Huerta1,2

Helena Iturribarría-Rojas2

William W. Shaw3

1104 Biological Sciences East

School of Natural Resources, University of Arizona

Tucson, AZ 85721

e-mail: [email protected]

2Pronatura Noroeste, Avenida Jalisco 903,

San Luis Río Colorado, Sonora, México. 83440.

3225 Biological Sciences East

School of Natural Resources, University of Arizona

Tucson, AZ 85721

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Abstract. The restoration of riparian systems in western North America deals with the challenge of scarce water resources and the prevalence of the invasive saltcedar

(Tamarix ramosissima). We evaluated the effect of vegetation type and the presence of surface water on the avian communities in the floodplain of the Colorado River in

Mexico during the summer of 2002 and 2003. Avian diversity and species richness was more influenced by the presence of water than by vegetation type. Bird abundance was more influenced by vegetation type, but water also had an important effect, as wet sites had higher bird abundance than dry sites with the same vegetation type, and saltcedar wet areas had similar avian abundance to native dry sites. The avian community composition was similar among habitat types, with only 7% of the variation explained by vegetation type and the presence of water, and an average Morisita-Horn value = 0.93 (± 0.02) of pairwise comparisons between habitat types. The major factors that appear to determine the ecological value for birds in riparian areas are vegetation biomass, structural diversity, and the presence of surface water. Those three components should be the focus for the management of riparian ecosystems. In the floodplain of the Colorado River in

Mexico, conservation efforts should be directed to the prevention of human-induced disturbances and the maintenance of water sources.

Key words: Colorado River, floodplain, instream flows, restoration, saltcedar.

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INTRODUCTION

The populations of at least 30 riparian dependant birds have been declining in Western

North America over the last 50 years, including not only riparian specialists, like Willow

Flycatcher and Yellow-billed Cuckoo, but also some generalists, like Song Sparrow and

Gila Woodpecker (DeSante and George 1994, Ballard et al. 2003). A major cause linked to these declines has been habitat loss, particularly the destruction of cottonwood-willow gallery forests (Ohmart 1994, Rich et al. 2003). The increasing dominance of saltcedar has also been postulated as a cause for avian population declines in riparian areas

(Anderson et al. 1977, Rosenberg et al. 1991, Ellis 1995).

Saltcedar dominated areas in riparian systems have been found to have lower bird species richness and densities than cottonwood-willow dominated sites (Anderson et al.

1977, Cohan et al. 1978); and some guilds occur only in native riparian forests (Hunter et al. 1988, Rosenberg et al. 1991, Ellis 1995). However, relatively high bird richness and densities have been observed in some saltcedar areas, comparable to native riparian sites

(Brown and Johnson 1987, Hunter et al. 1988, Ellis 1995, Fleishman et al. 2003), and some endangered or sensitive species have been nesting in saltcedar dominated areas, including the Southwestern Willow Flycatcher, Yellow-billed Cuckoo, and Yellow

Warbler (Hunter et al. 1988, Rosenberg et al. 1991, Sogge et al. 1997). Furthermore, species richness has been found to be best explained by vegetation volume, and the dominance of saltcedar was found to have no effect on species richness, abundance or evenness of birds (Fleishman et al. 2003).

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The ecological value of saltcedar for birds depends at least on the geographic region, vegetation biomass and habitat structure of a site (Hunter et al. 1988, Fleishman et al. 2003, Shafroth et al. 2005), as well as on the feeding behavior, nesting requirements and seasonal status of the bird species in a particular region (Rosenberg et al. 1991, Ellis

1995, Shafroth et al. 2005).

The role of instream flows or presence of surface water has not been evaluated as a potential factor in determining the relative ecological value of saltcedar compared to native riparian trees. Surface water might have a strong confounding effect in studies that compare habitat value for birds of saltcedar and native vegetation, as saltcedar tends to dominate in areas exposed to extended desiccation, while native vegetation tends to dominate in areas exposed to periodic pulse flood events, near surface water or shallow groundwater (Vandersande et al. 2001, Stromberg and Chew 2002, Glenn and Nagler

2005).

There are two current approaches for the management of saltcedar and restoration of riparian systems in Western North America. One approach proposes the large-scale eradication of saltcedar whenever and wherever possible via chemical or mechanical means, in order to improve habitat quality for wildlife, salvage water, reduce fire risk, and increase recreational value (Barrows 1998, Saltcedar Task Force 2004, Hart et al.

2005). An alternative approach proposes the restoration of the natural flood regimes and the maintenance of a sustainable mix of saltcedar and native trees, which in conjunction could maintain the ecological functions and biodiversity of the original riparian systems

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(Anderson 1998, Sher et al. 2000, Stromberg and Chew 2002, Glenn and Nagler 2005,

Nagler et al. 2005).

Our goal was to evaluate the bird habitat values of saltcedar and identify plausible restoration guidelines for riparian ecosystems and native birds in the presence of saltcedar. In particular, we assessed the difference in avian richness, diversity, and abundance values between cottonwood-willow sites and saltcedar sites, with similar vegetative biomass and similar conditions of surface water.

METHODOLOGY

STUDY AREA

The study area encompasses the floodplain of the Colorado River in Mexico, from

Morelos Dam downstream to the confluence of the Colorado with the Hardy River

(Figure 1). The floodplain traverses the Mexicali Valley as the river flows toward the

Gulf of California, and is surrounded by flood control levees on each margin. The total area is 43 000 ha, and includes 150 kilometers of river. This includes the main stem of the Colorado, secondary streams, backwater lagoons, and the portion of the major agricultural drains that are within the floodplain. Water flows in the area have been intermittent since the completion of Hoover Dam (1937), depending upon excess deliveries from the U.S. to Mexico, administrative losses from the Mexicali Irrigation

District and agricultural drainage water.

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The floodplain of the Colorado River in Mexico has an average vegetation cover of 70%, of which 88% is comprised by shrubs and trees (Hinojosa-Huerta et al. unpublished). Native plants average a cover of 33.71%, while exotic plants cover

36.74%. Cottonwoods (Populus fremontii) and willows (Salix gooddingii) cover 8% of the floodplain (Hinojosa-Huerta et al. unpublished). Saltcedar is the most common shrub, followed by arroweed (Pluchea sericea), seep willow (Baccharis spp.), and saltbush

(Atriplex spp; Nagler et al. 2005).

SURVEY SITES

We randomly placed 175 survey sites within the study areas, classified in 4 groups: 1- sites dominated by cottonwoods and/or willows, with surface water (Native Wet, n = 50),

2-sites dominated by cottonwoods and/or willows, without surface water (Native Dry, n =

31), 3-sites dominated by saltcedar, with surface water (Saltcedar Wet, n = 44), and 4- sites dominated by saltcedar, without surface water (Saltcedar Dry, n = 50). The position at each survey site (UTM, NAD 1927 Mexico) was recorded using a handheld GPS receiver (Garmin Etrex).

All of the selected sites had at least 50% vegetation cover. Native sites had at least

15% cover by cottonwood and/or willow trees, with these species dominant in the mid- and overstory. Saltcedar sites had at least 30% cover of saltcedar and no cottonwoods, willows or mesquite. Wet sites had between 5 and 30% cover of open water continuously

(> 1 cm deep). Dry sites had 0% surface water and were located at least 400 m from

172 surface water. Both wet and dry sites met these conditions for at least 2 years before this study was conducted. The original design consisted of 50 sites in each category, but during the study 19 Native Dry sites were flooded and 6 Saltcedar Wet sites dried out, and were removed from the analysis.

The information for the selection of sites was based on a vegetation map of the floodplain, created with satellite image and aerial photography (Nagler et al. 2005) and on extensive habitat measurements collected on 240 sites throughout the study area

(Hinojosa-Huerta et al. unpublished).

HABITAT SURVEYS

We measured habitat features at the 175 survey sites (50 m radius) once per year, during the summer (June-July), in order to verify the adequacy of the categorization of sites, and to compare the vegetation density, the vegetation structure, and the percent cover of surface water (at wet sites), testing the null hypothesis of no difference between categories. At each station we estimated the percent coverage, and the minimum, maximum, and average height of each of the following strata: trees (vegetation >3 m in height), shrubs (0.5 – 3 m), herbs (0.1 – 0.5 m), forbs (< 0.1 m), emergent plants, bare soil, and open water. We then categorized each strata by estimating the percent coverage and average height of each plant species within a stratum. We measured the diameter at breast height (dbh) of five individuals from each species present at the tree stratum. For open water, we recorded type (primary or secondary stream, drain, irrigation canal, or

173 lagoon), depth, and width. The estimates of land cover were obtained with the aid of measuring tapes, the GPS receivers, and pacing. The data were used to corroborate the classification of sites and verify that the habitat conditions were met. The habitat structural diversity was calculated using the Shannon index of diversity (H’ vegetation =

Σ pilnp, where pi is the percent vegetation cover found at the ith stratum; Scott et al.

2003).

BIRD SURVEYS

We conducted bird counts following a variable distance point count methodology (Ralph et al. 1996) at the selected sites, 3 times every summer (once per month from May to

July) during 2002 and 2003.

Surveys were conducted by teams of two persons starting at sunrise and until no later than 4 hours after sunrise. At each survey station we counted all birds heard or seen within a 5 min period, estimating distance to the observer. The effective detection radius for the bird counts at each point was 57.14 m (± 1.00), based on an estimate using the program DISTANCE (Thomas et al. 2002).

STATISTICAL ANALYSES

Detections of flyover birds were excluded from the analyses. Bird species were assigned to a foraging guild (based on Ehrlich et al. 1988) and a residency status guild (based on species status in the region, following Patten et al. 2001 and Hinojosa-Huerta et al. 2006,

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Table 1). We used JMP IN 3.1 (Sall and Lehman 1996) and SYSTAT 10.2 (SYSTAT

Software Inc. 2002) for the statistical analyses. Abundance data for all species were used to calculate the ecological indices.

We applied the Shapiro-Wilk W test to the data sets to test for normality and plotted the distributions of the data sets and the residuals of the analyses in order to verify the robustness of the procedures. We used a t-test to compare the indices between years, and ANOVA to test if the difference was consistent among habitat types.

We performed ANOVA and Turkey-Kramer tests pooling the data of 2002 and

2003 to compare different response variables among habitat groups: 1- the average species richness (average number of species detected per point per survey), 2- the average bird abundance (average total individuals detected per point per survey), 3- the diversity per point (Hill’s N2 and the Shannon index of diversity H’ birds), and 4- the evenness per

point (Hill’s N2/N1 ratio and Pielou’s J). For formulas on the diversity and evenness indices see Hayek and Buzas (1997). We used the program CANOCO 4.53 (ter Braak and Šmilauer 2002) to calculate the diversity and evenness indices.

We used the program EstimateS 7.5 (Colwell 2005) to compare the avian communities between habitat types. We made pair-wise calculations of the Jaccard Index

as an indicator of the qualitative similarity among groups (shared species), and the

Morisita-Horn Index as a quantitative indicator of community similarity (shared species

and their relative abundance; Magurran 2004).

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To evaluate the community composition along a vegetation gradient (Native-

Saltcedar) and along a water cover gradient (Dry-Wet), we used canonical correspondence analysis (CCA), performed with CANOCO 4.53 (ter Braak and Šmilauer

2002). CCA is a constrained ordination technique based on regression analysis in a multivariate space, incorporating the unimodal response of species to environmental variables, in order to find the variability in species composition explained by the environmental variables (Lepš and Šmilauer 2003, ter Braak and Šmilauer 2002).

The species data consisted of the total count of individuals in each species per survey site. The environmental data consisted of four nominal variables for each site:

Native (sites dominated by cottonwoods and/or willows), Saltcedar (sites dominated by saltcedar), Wet (sites with surface water), and Dry (sites without surface water). For the analysis we used biplot scaling, focusing on inter-species distances. We performed a

Monte Carlo randomization test (500 random permutations) on the projected relationships

(ter Braak and Šmilauer 2002) to evaluate the significance of the environmental variables in explaining the species composition.

We evaluated the effect of each environmental gradient on species richness (total number of species per point), abundance (total number of species per point), diversity (N2

and H’ birds) and evenness (N2/N1 and J) by performing multivariate regressions in a

general linear model and Gaussian distribution of these response variables against the

environmental variables. We used CanoDraw 4.12 (ter Braak and Šmilauer 2002) for the

analyses. We also performed the multivariate tests using H’ vegetation as a covariable, in

order to control for the effect of the difference of habitat structural diversity among sites.

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The values reported in the Results are means ± SE. We used a significance level of 0.05 for all statistical tests.

RESULTS

HABITAT MEASUREMENTS

The average vegetation cover at the survey sites in the floodplain of the Colorado River in Mexico was 74% (± 1.03), with no difference detected among groups (F3,171 = 0.27, P

= 0.88, Table 2). The average water cover at the wet sites was 10% (± 0.72), with no

difference among them (Turkey-Kramer P = 0.36, Table 2). The average percent cover by

trees at the survey sites was 32% (± 1.32), with no difference among groups (F3,171 =

1.65, P = 0.18).

The average percent cover by shrubs was 34% (± 1.31), with some differences among habitat types (F3,171 = 12.30, P < 0.001, Table 2).The percent cover of shrubs was significantly higher at Saltcedar Dry sites than at Native Wet and Saltcedar Wet sites, and

the shrub cover was significantly higher at Native Dry sites than at Native Wet sites

(Table 3). The cover of emergent vegetation was higher at wet sites than at dry sites

(F3,171 = 22.28, P < 0.001, Table 2 and 3) and the cover of herbs was higher at Native Dry

sites than at saltcedar sites (F3,171 = 6.62, P < 0.001, Table 2 and 3) The vegetation

structural diversity was different among sites (F3,171 = 46.35, P < 0.001, Table 2), as it

was higher at the Native and Saltcedar Wet sites (no difference among them, Turkey-

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Kramer P = 0.20), 16% lower at the Native Dry sites (Turkey-Kramer P < 0.001), and

32% lower at the Saltcedar Dry sites (Turkey-Kramer P < 0.001, Table 3).

BIRD COUNTS

We counted a total of 19 386 birds representing 120 species during the six summer visits of 2002 and 2003 in the Colorado River floodplain in Mexico (Table 4). The overall average bird abundance per point was 20.12 individuals (± 0.48) and the overall avian species richness per point was 9.23 species (± 0.15). The average bird abundance was higher in 2003 than in 2002 (mean difference of 5.47 individuals, ± 0.64, two-tailed t174 =

8.50, P < 0.001). This difference was consistent among groups (F3,171 = 2.19, P = 0.09),

and the data had a similar pattern in both years in terms of the ranking of abundance

among groups (Table 5).

The average species richness per point was also higher in 2003 than in 2002

(mean difference of 1.27 species, ± 0.21, two-tailed t174 = 6.04, P < 0.001). The mean

difference of species richness per point between 2002 and 2003 was also consistent

among groups (F3,171 = 0.87, P = 0.46), maintaining a similar pattern in both years (Table

5).

The indices of diversity at each point (N2 and H’ birds) were not different between

2002 and 2003 (two-tailed t174 = 0.52 and -0.16, P = 0.61 and 0.87 respectively). The

evenness indices (N2/N1 and J) were slightly higher in 2002 than in 2003 (mean

difference of 0.02 in both cases, two-tailed t174 = 2.21 and 3.98, P = 0.02 and 0.001

178

respectively), and the differences were consistent among habitat groups (F3,171 = 0.83 and

0.97, P = 0.47 and 0.42 respectively).

ABUNDANCE AND SPECIES RICHNESS

Average bird abundance per point was different among groups (F3,171 = 18.97, P <

0.001), being higher at the Native Wet sites (Table 5, Figure 2). Average bird abundance

was similar in the Native Dry and Saltcedar Wet sites, both about 15% lower than at

Native Wet, while abundance was lower at Saltcedar Dry (35% lower than Native Wet

and about 23% lower than Saltcedar Wet and Native Dry, Table 6).

Average species richness among the groups also differed (F3,171 = 22.86, P <

0.001, Table 5, Figure 3). Saltcedar Dry sites had lower average species richness than all other groups: 15%, 21%, and 26% lower than Native Dry, Saltcedar Wet and Native Wet respectively (Table 6). The average species richness was 14% lower at Native Dry than at

Native Wet. Species richness of Saltcedar Wet sites was not significantly different than

Native Wet or Native Dry sites (about 7% difference, P > 0.25, Table 6).

DIVERSITY AND EVENNESS

The average value of H’ birds was 2.64 (± 0.02) and the average value of N2 was 10.71 (±

0.23, Table 7). Both diversity indices were different among groups (F3,171 = 17.31, P <

0.001 for N2 and F3,171 = 23.89, P < 0.001 for H’ birds, Figure 4 and 5). The difference was not significant within wet sites (difference of 3% and 0.1% for N2 and H’ birds

179

respectively, Turkey-Kramer P > 0.8) or within dry sites (difference of 5% and 3% for N2 and H’ birds respectively, Turkey-Kramer P > 0.4, Table 6). The dry sites had lower diversity values than the wet sites: an average 24% lower in N2 (Turkey-Kramer P <

0.001) and 9.7% lower for H’ birds (Turkey-Kramer P < 0.001, Table 6).

The average value of N2/N1 measure of evenness was 0.73 (± 0.005) and the average value of J was 0.85 (± 0.003, Table 7). N2/N1 was no different among groups

(F3,171 = 1.92, P = 0.12, Table 6). J was different only between Saltcedar Wet and Native

Dry sites (F3,171 = 4.47, P = 0.005, Turkey-Kramer P = 0.002), but the difference was

only of 3% (lower at Native Dry sites, Table 6).

COMMUNITY COMPOSITION

The percent of shared species between pairs of groups (Jaccard Index) was on average

63% (± 2), being higher between Native Dry and Saltcedar Dry, and lower between

Native Dry and Saltcedar Wet (Table 8). The quantitative comparisons between pairs of

groups (Morisita-Horn Index) had an average value of 0.93 (± 0.02), where 1 means

identical community composition. The higher value occurred between Native Dry and

Saltcedar Dry and the lower value occurred between Native Dry and Saltcedar Wet

(Table 8).

The top 3 overall ranking species (ranking within the top 5 in all habitat types)

were Mourning Dove, Verdin and Brown-headed Cowbird, together comprising 33% of

all detections (Table 9). The top 25 ranking species comprises 90% of all records, with

180 almost all of these species ranking within the top 25 in all habitat types, except for Marsh

Wren (rank 43 and 47 in Native Dry and Saltcedar Dry respectively), Snowy Egret (33,

28, and 48 in Native Dry, Native Wet, and Saltcedar Dry), Common Moorhen (34 in

Native Dry and 52 in Saltcedar Dry), Crissal Thrasher (26 in Native Dry and 30 in

Saltcedar Wet), Lesser Nighthawk (45 in Native Wet) and Hooded Oriole (37 in

Saltcedar Wet, Table 9).

Twenty of the detected species were not observed at the Native sites combined

(Table 9). All of those species were rare during the study (together comprise 0.2% of all detections), and 18 of them were species with < 10 total detections. Most of the missing species were migratory, except for Foster’s Tern and Gull-billed Tern. Twenty one species were not observed at the Saltcedar sites (Table 9). These species were also rare in the area (0.2% of all detections) and mostly migratory, except for American Kestrel,

Yellow-billed Cuckoo, Black-chinned Hummingbird, Costa’s Hummingbird, House

Finch, Horned Lark and Lesser Goldfinch.

Only 4 species were not detected at the Wet sites combined, all of them only observed once during the study (Table 9). In contrast, 42 species were not detected at the

Dry sites, although together these species comprise only 1% of all detections (Table 9).

Some of these species were not rare in Wet sites (> 30 detections), including Pied-billed

Grebes, Clapper Rails, and Caspian Terns. Other species of significance missing from the

Dry sites include Yellow-billed Cuckoo, Bell’s Vireo, and Black-chinned Hummingbird.

Saltcedar sites had a larger total number of detections of breeding, resident, and migratory waterbirds, while Native sites had a larger total number of detections of

181 breeding landbirds Table 9, Figure 6). Resident landbirds and migratory landbirds had a similar number of detections among Saltcedar and Native sites (difference < 5%).

Saltcedar sites had more detections of birds in all waterbird foraging guilds (except dense vegetation waders), while Native sites had more detections of nectar feeders (100% of the detections), scavengers, timber drillers, flycatchers and predators (Table 10, Figure 7).

The difference in detections on ground-slash foragers, timber-foliage searchers, and dense vegetation waders was < 5%. Wet sites had more bird detections across all residency status and foraging guilds, except for predators, flycatchers, and breeding landbirds, in which detections were similar among Wet and Dry sites (difference < 4%,

Table 9, Figure 7).

CANONICAL CORRESPONDENCE ANALYSIS

The two canonical axes of the environmental gradients explained 7% of the variation in avian community composition among sites in the CCA analysis (Figure 8). The Wet-Dry axis was 3.8 times more important in explaining the variation in community composition of the surveyed sites (Monte Carlo permutation test, F2,173 = 8.85, P = 0.02, eigenvalue =

0.07), also explaining 79% of the variation in the species-environment relation. Although

of secondary importance, the Native-Saltcedar axis was also significant in explaining the variation in community composition (Monte Carlo permutation test, F2,173 = 3.22, P =

0.02, eigenvalue = 0.02).

182

Species richness was associated with both environmental axes (F3,172 = 41.19, P <

0.001), with a 15% larger effect produced by the Wet-Dry gradient (Figure 9). The

diversity indices shared a similar pattern, with the N2 model (F3,172 = 25.45, P < 0.001)

showing an effect of the Wet-Dry gradient 2.59 times larger than the Native-Saltcedar

gradient (Figure 10), and the H’ birds model (F3,172 = 35.10, P < 0.001) showing an effect of the Wet-Dry gradient 1.9 times larger than the Native-Saltcedar gradient (Figure 11).

Abundance was also associated with both environmental axes (F3,172 = 22.51, P < 0.001),

but the Native-Saltcedar gradient had an effect 3 times larger than the Wet-Dry gradient.

N2/N1 was weakly associated with the environmental gradients (F3,172 = 2.88, P = 0.06),

with the Wet-Dry gradient having no effect, and evenness increasing 3% towards

Saltcedar sites in the vegetation type gradient. The model J with the environmental gradient was significant (F3,172 = 6.74, P = 0.002), but the vegetation type gradient was

not significant and the Wet-Dry gradient showed an increase of 3% towards wet sites.

After controlling for habitat structural diversity (as a covariable in the CCA

model), the patterns and significance of the environmental gradients were maintained, but

the two canonical axis of the environmental gradients only explained 3% of the variation

in avian community composition among sites. The relationships and significances of

species richness, N2, H’ birds, abundance, and J with the environmental gradients were also maintained after controlling for structural diversity. The relative associations of

N2/N1 with the environmental gradients were similar after controlling for structural

diversity, but were not significant (F3,172 = 2.51, P = 0.08).

183

DISCUSSION

In the Colorado River delta, the diversity of birds was more influenced by the presence of surface water than by vegetation type. On the other hand, bird abundance was more influenced by vegetation type, but surface water also had an important effect. Wet sites had significantly higher bird abundance than dry sites with the same vegetation type, and wet saltcedar areas had average abundance very similar to dry native sites. In all cases, the presence of water was an important factor determining the richness, abundance, and diversity of birds at both native riparian and saltcedar areas. Saltcedar areas with surface water had avian characteristics similar to native riparian sites. Community composition also appeared to be more influenced by differences in water conditions than by vegetation type.

Several ecological processes might be involved in the observed patterns of avian indices in relation to water conditions and vegetation type (Figure 12). As the percent cover of water increases along with vegetation structural diversity and biomass, more niches appear to be available, and thus more species could be present at a site (Tews et al.

2004). The availability of food resources and improved micro-climate conditions might also play a role in the observed patterns.

Insect biomass in saltcedar areas has been found to be similar to or even greater than in native riparian trees (Cohan et al. 1978, Drost et al. 2001, Anderson et al. 2004,

Yard et al. 2004). Additionally, an increase in stream edge and stream area has been found to increase insect diversity and biomass, and the abundance of insectivorous birds

(Gray 1993, Iwata et al. 2003, Naiman et al. 2005). Finally, the maintenance of instream

184 flows and pulse floods has been associated with increased productivity in riparian systems (Richter and Richter 2000, Zamora-Arroyo et al. 2001, Nagler et al. 2005).

The role of foliage density, canopy structure and surface water has also been explored in terms of the micro-climate effect on breeding birds in the riparian areas of the

Southwestern U.S. The results suggest that due to the extreme temperatures during summer, reaching over 45° C, breeding birds tend to prefer areas in which physical conditions maintain lower canopy temperatures, resulting from the shade and evapotranspiration of dense foliage and the presence of water (Hunter et al. 1988, Allison et al. 2003, Brodhead 2005). In the Colorado River delta, multi-layered, dense foliage and the presence of surface water might have a significant role in terms of creating adequate micro-climate conditions for breeding riparian birds.

An alternative explanation for the patterns that we observed is that surface water and vegetation biomass might be strong cues for the selection of territories by birds, and that wet saltcedar sites might present those cues. Therefore, saltcedar dominated sites present relatively high values of avian density and richness, but might function as ecological traps (Schlaepfer et al. 2002), with high mortality rates and/or low productivity. In order to test this explanation, we need additional research to evaluate avian productivity and survivorship at different vegetation types. Research on the Southwestern Willow

Flycatcher has shown that saltcedar sites have similar productivity and survivorship values than native riparian sites (Owen et al. 2005). This suggests that saltcedar areas are not ecological traps, at least for the Southwestern Willow Flycatcher, but additional research is required to evaluate the effect on a variety of riparian dependant birds.

185

IMPLICATIONS FOR RESTORATION

The decline of native riparian forests has not been caused simply by direct competition with saltcedar, but by major disruptions of hydrological regimes in the rivers of Western

North America, including the modification or elimination of pulse flood events, canalization of streams, lowering of groundwater levels, and the elimination or reduction of instream flows (Stromberg 1998, Glenn et al. 2001, Shafroth et al. 2005, Nagler et al.

2005). These disruptions have created terraces and banks subject to extended periods of desiccation and higher salt concentrations, which are not suitable for most of the native riparian plants, but adequate for saltcedar colonization (Vandersande et al. 2001,

Stromberg and Chew 2002, Glenn and Nagler 2005).

At the same time, current economical, social and political conditions preclude the feasibility of full-scale restoration to pre-dam conditions (Fleishman et al. 2003, Shafroth et al. 2005). However, existing floodplains and water resources could be managed in a way that can mimic historic flooding regimes, such that ecologically functional riparian systems can be maintained in the long-term, although in reduced sizes.

Considering results from previous studies (Anderson et al. 1983, Ellis 1995,

Fleishman 2003) and our findings, three major factors appear to be key in determining the ecological value (at least for birds) of a riparian area: total vegetation biomass, structural diversity, and the presence of surface water. Those three components should be the focus of management and restoration efforts of riparian areas in the Sonoran Desert.

186

The regular incidence of instream flows and pulse floods in the Colorado River floodplain in Mexico during the last 20 years, although unintentional, has restored the ecological functions of this riparian system in a geographically limited but biologically significant way. The vegetation matrix of saltcedar and native trees appears to be able to sustain an abundant and diverse avifauna. However, not all habitat types within the riparian structure and not all of the bird species have recuperated. This seem to be a function of the lack of older-larger stands of native trees, which apparently do not exist in the floodplain due to human-induced effects, such as wildfires and logging (Nagler et al.

2005). Thus, conservation efforts should be directed to the prevention of the human- induced disturbances and maintenance of water sources.

Resource managers must evaluate management alternatives with consideration of their effectiveness in accomplishing management goals as well as the economic feasibility of implementing a given strategy. This study focused on determining which environmental variables are most powerful in creating habitats for riparian birds in the

Sonoran Desert region and specifically, the Colorado River Delta.

This is an environment in which saltcedar has invaded and established vast stands and some authors have suggested that removal of salt cedar (if it were feasible), could be an important strategy for enhancing bird habitats in the region (Barrows 1998, Hart et al.

2005). While there may be many valid environmental arguments for eliminating invasive exotic plants, the findings of this study suggest that when the goal is to enhance riparian bird habitats, emphasis should be placed on management strategies that result in more surface water rather than upon elimination of saltcedar. Saltcedar, in the presence of

187 surface water, provides habitats for a diverse and abundant avifauna. When compared with native vegetation, the value of saltcedar stands in the presence of surface water was either equivalent or only slightly less valuable as bird habitats. On the other hand, the absence of surface water in either native or saltcedar stands had dramatic negative effects.

Managing stream flows to increase areas covered with surface waters may actually have additional effects of favoring native vegetation over saltcedar. Several authors (Glenn et al. 2001, Stromberg and Chew 2002, Nagler et al. 2005, Tiegs et al.

2005) have indicated that allowing periodic pulse flows of water in the Colorado River and the maintenance of modest instream flows would result in more native trees. Since these flows would also significantly increase surface waters, the results of this study suggest that such a strategy would have major benefits for riparian birds, even in areas where saltcedar persists.

ACKNOWLEDGEMENTS

Our special gratitude to Juan Butrón, José Juan Butrón, Alejandra Calvo, Victor Ortega,

Juan Rivera, Gerardo Sánchez, Pablo Valle, Michael Vamstad, Enrique Zamora, Alberto

Zepeda and the numerous volunteers that helped during field activities. Our work has been possible thanks to Sacha Heath, Chris McCreedy, Roy Churchwell and Steve Latta

(PRBO Conservation Science), Robert Mesta (Sonoran Joint Venture), Yamilett Carrillo,

Meredith de la Garza and Raquel Castro (Pronatura Sonora), Consejo Nacional de

Ciencia y Tecnología (CONACyT), the National Fish and Wildlife Foundation and the

Wallace Foundation. Comments from Courtney Conway, Kevin Fitzsimmons, Edward

188

Glenn, William Mannan, and Alberto Macias provided insight for the analysis and discussion.

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Table 1. Bird species detected during 2002 and 2003 summer surveys in the floodplain of the Colorado River, Mexico. Taxonomic nomenclature and order follow the American

Ornithologists’ Union (AOU 1998, Banks et al. 2004). Four-letter codes follow Pyle

(1997). Feeding guilds follow Ehrlich et al. (1988). Residency status guilds are based on the status of species in the region, and follow Patten et al. (2001) and Hinojosa-Huerta et al. (2006).

Four Letter Feeding Residency Common Name Scientific Name Code Guild1 Status Guild2 Mallard Anas platyrhynchos MALL DDF Mig WB Cinnamon Teal Anas cyanoptera CITE DDF Br WB Common Merganser Mergus merganser COME D Mig WB Gambel's Quail Callipepla gambelii GAQU GS Res LB Pied-billed Grebe Podilymbus podiceps PBGR D Res WB Eared Grebe Podiceps nigricollis EAGR D Mig WB American White Pelican Pelecanus erythrorhynchos AWPE AP Mig WB Brown Pelican Pelecanus occidentalis BRPE AP Mig WB Double-crested Cormorant Phalacrocorax auritus DCCO D Mig WB American Bittern Botaurus lentiginosus AMBI DVW Br WB Least Bittern Ixobrychus exilis LEBI DVW Res WB Great Blue Heron Ardea herodias GBHE OWW Res WB Great Egret Ardea alba GREG OWW Res WB Snowy Egret Egretta thula SNEG OWW Res WB Reddish Egret Egretta rufescens REEG OWW Mig WB Cattle Egret Bubulcus ibis CAEG GS Res LB Green Heron Butorides virescens GRHE DVW Res WB Black-crowned Night- Heron Nycticorax nycticorax BCNH DVW Res WB White-faced Ibis Plegadis chihi WFIB MSF Mig WB Wood Stork Mycteria americana WOST OWW Br WB Turkey Vulture Cathartes aura TUVU S Res LB Osprey Pandion haliaetus OSPR AP Res WB White-tailed Kite Elanus leucurus WTKI P Br LB Northern Harrier Circus cyaneus NOHA P Mig LB Red-tailed Hawk Buteo jamaicensis RTHA P Mig LB American Kestrel Falco sparverius AMKE P Res LB Peregrine Falcon Falco peregrinus PEFA P Mig LB Yuma Clapper Rail Rallus longirostris CLRA DVW Res WB

197

Common Moorhen Gallinula chloropus COMO DDF Res WB American Coot Fulica americana AMCO DDF Res WB Semipalmated Plover Charadrius semipalmatus SEPL MSF Mig WB Killdeer Charadrius vociferus KILL MSF Res WB Black-necked Stilt Himantopus mexicanus BNST MSF Res WB Greater Yellowlegs Tringa melanoleuca GRYE MSF Mig WB Lesser Yellowlegs Tringa flavipes LEYE MSF Mig WB Solitary Sandpiper Tringa solitaria SOSA MSF Mig WB Willet Catotrophorus semipalmatus WILL MSF Mig WB Spotted Sandpiper Actitis macularia SPSA MSF Mig WB Whimbrel Numenius phaeopus WHIM MSF Mig WB Marbled Godwit Limosa fedoa MAGO MSF Mig WB Western Sandpiper Calidris mauri WESA MSF Mig WB Least Sandpiper Calidris minutilla LESA MSF Mig WB Short-billed Dowitcher Limnodromus griseus SBDO MSF Mig WB Long-billed Dowitcher Limnodromus scolopaceus LBDO MSF Mig WB Ring-billed Gull Larus delawarensis RBGU MSF Mig WB California Gull Larus californicus CAGU MSF Mig WB Gull-billed Tern Sterna nilotica GBTE AP Res WB Caspian Tern Sterna caspia CATE AP Res WB Forster's Tern Sterna forsteri FOTE AP Res WB White-winged Dove Zenaida asiatica WWDO GS Br LB Mourning Dove Zenaida macroura MODO GS Res LB Inca Dove Columbina inca INDO GS Res LB Common Ground-Dove Columbina passerina COGD GS Res LB Yellow-billed Cuckoo Coccyzus americanus YBCU TFS Br LB Greater Roadrunner Geococcyx californianus GRRO P Res LB Barn Owl Tyto alba BNOW P Res LB Burrowing Owl Athene cunicularia BUOW P Res LB Lesser Nighthawk Chordeiles acutipennis LENI F Br LB Black-chinned Hummingbird Archilochus alexandri BCHU N Br LB Costa's Hummingbird Calypte costae COHU N Res LB Allen's Hummingbird Selasphorus sasin ALHU N Mig LB Belted Kingfisher Ceryle alcyon BEKI AP Mig WB Gila Woodpecker Melanerpes uropygialis GIWO TD Res LB Ladder-backed Woodpecker Picoides scalaris LBWO TD Res LB Western Wood-Pewee Contopus sordidulus WEWP F Mig LB Willow Flycatcher Empidonax traillii WIFL F Mig LB Pacific-slope Flycatcher Empidonax difficilis PSFL F Mig LB Black Phoebe Sayornis nigricans BLPH F Res LB Vermilion Flycatcher Pyrocephalus rubinus VEFL F Res LB Ash-throated Flycatcher Myiarchus cinerascens ATFL F Res LB Western Kingbird Tyrannus verticalis WEKI F Br LB Loggerhead Shrike Lanius ludovicianus LOSH P Res LB

198

Bell's Vireo Vireo bellii BEVI TFS Mig LB Warbling Vireo Vireo gilvus WAVI TFS Mig LB American Crow Corvus brachyrhychos AMCR GS Mig LB Common Raven Corvus corax CORA GS Res LB Horned Lark Eremophila alpestris HOLA GS Res LB Tree Swallow Tachycineta bicolor TRES F Mig LB Violet-green Swallow Tachycineta thalassina VGSW F Mig LB Northern Rough- winged Swallow Stelgidopterx serripennis NRWS F Res LB Cliff Swallow Petrochelidion pyrrhonata CLSW F Res LB Verdin Auriparus flaviceps VERD TFS Res LB Campylorhynchus Cactus Wren brunneicapillus CACW TFS Res LB Bewick's Wren Thryomanes bewickii BEWR TFS Mig LB Marsh Wren Cistothorus palustris MAWR TFS Res LB Blue-gray Gnatcatcher Polioptila caerulea BGGN TFS Mig LB Black-tailed Gnatcatcher Polioptila melanura BTGN TFS Res LB Swainson's Thrush Catharus ustulatus SWTH GS Mig LB Northern Mockingbird Mimus polyglottos NOMO TFS Res LB Crissal Thrasher Toxostoma crissale CRTH GS Res LB Orange-crowned Warbler Vermivora celata OCWA TFS Mig LB Nashville Warbler Vermivora ruficapilla NAWA TFS Mig LB Yellow Warbler Dendroica petechia YWAR TFS Mig LB Yellow-rumped Warbler Dendroica coronata YRWA TFS Mig LB Black-throated Gray Warbler Dendroica nigrescens BTYW TFS Mig LB Townsend's Warbler Dendroica townsendi TOWA TFS Mig LB Hermit Warbler Dendroica occidentalis HEWA TFS Mig LB Common Yellowthroat Geothlypis trichas COYE TFS Res LB Wilson's Warbler Wilsonia pusilla WIWA TFS Mig LB Yellow-breasted Chat Icteria virens YBCH TFS Br LB Western Tanager Piranga ludoviciana WETA TFS Mig LB Abert's Towhee Pipilo aberti ABTO GS Res LB Song Sparrow Melospiza melodia SOSP TFS Res LB Lincoln's Sparrow Melospiza lincolnii LISP GS Mig LB Dark-eyed Junco Junco hyemalis DEJU GS Mig LB Black-headed Grosbeak Pheuticus melanocephalus BHGR TFS Mig LB Blue Grosbeak Guiraca caerulea BLGR TFS Br LB Red-winged Blackbird Agelaius phoeniceus RWBL TFS Res LB Western Meadowlark Sturnella neglecta WEME GS Res LB Yellow-headed Xanthocephalus Blackbird xanthocephalus YHBL TFS Res LB Great-tailed Grackle Quiscalus mexicanus GTGR GS Res LB Brown-headed Cowbird Molothrus ater BHCO GS Res LB

199

Hooded Oriole Icterus cucullatus HOOR TFS Br LB Bullock's Oriole Icterus bullockii BUOR TFS Br LB House Finch Carpodacus mexicanus HOFI GS Res LB Lesser Goldfinch Carduelis psaltria LEGO GS Br LB Ring-necked Pheasant3 Phasianus colchicus RNEP GS Res LB Rock Dove3 Columba livia RODO GS Res LB European Starling3 Sturnus vulgaris EUST GS Res LB House Sparrow3 Passer domesticus HOSP GS Res LB

1Feeding guilds: AP = Aerial Piscivore, D = Diver, DDF = Dipping/Dabbling Forager, DVW = Dense Vegetation Wader, F = Flycatcher, GS = Ground or Slash Forager, MSF = Moist Soils Forager, N = Nectar Feeder, OWW = Open Water Wader, P = Predator on Vertebrates, TD = Timber Driller, and TFS = Timber-Foliage Searcher.

2 Residency Status Guilds: Br LB = Breeding Landbird, Mig LB = Migratory Landbird, Res LB = Resident Landbirds, Br WB = Breeding Waterbird, Mig WB = Migratory Waterbird, Res WB = Resident Waterbird.

3Introduced species

200

Table 2. Average habitat characteristics of the survey sites by habitat type in the floodplain of the Colorado River, Mexico (2002 and 2003). Standard errors are shown in parenthesis. The habitat structural diversity was calculated using the Shannon index of diversity.

Veg Water Cover Trees Shrubs Emergent Herbs Forbs Cover H' veg

Native 75.48 36.54 35.64 1.51 4.35 1.08 Dry (2.47) (3.20) (2.84) (1.26) (0.69) 0 0 (0.04)

Native 73.14 33.52 26.10 11.20 2.12 0.20 11.30 1.38 Wet (1.94) (2.52) (2.24) (0.99) (0.54) (0.05) (0.72) (0.03)

Saltcedar 74.80 28.08 45.00 1.18 0.74 0.88 Dry (1.94) (2.52) (2.24) (0.99) (0.54) 0 0 (0.03)

Saltcedar 74.75 33.47 32.25 8.09 0.93 9.56 1.29 Wet (2.07) (2.68) (2.39) (1.06) (0.58) 0 (0.72) (0.03)

201

Table 3. Matrix of pairwise average differences of habitat features between habitat types in the floodplain of the Colorado River, Mexico. The matrix only includes features in which an ANOVA test among habitat types was significant. Comparison probabilities of

Turkey-Kramer tests are shown in parenthesis.

Saltcedar Shrubs Native Dry Native Wet Saltcedar Dry Wet Native Dry 0 Native Wet -9.5 (0.04) 0 Saltcedar Dry 9.4 (0.05) 18.9 (< 0.01) 0 Saltcedar Wet -3.4 (0.80) 6.1 (0.24) -12.7 (<0.01) 0 Emergent Native Dry 0 Native Wet 9.7 (< 0.01) 0 Saltcedar Dry -0.3 (0.99) -10.0 (< 0.01) 0 Saltcedar Wet 6.6 (0< 0.01) -3.1 (0.1) 6.9 (< 0.01) 0 Herbs Native Dry 0 Native Wet -2.3 (0.06) 0 Saltcedar Dry -3.6 (< 0.01) -1.4 (0.28) 0 Saltcedar Wet -3.4 (< 0.01) -1.2 (0.46) 0.2 (99) 0 H' vegetation Native Dry 0 Native Wet 0.3 (<0.01) 0 Saltcedar Dry -0.2 (<0.01) -0.5 (< 0.001) 0 Saltcedar Wet 0.2 (<0.01) -0.1 (0.20) 0.4 (< 0.01) 0

202

Table 4. Number of survey sites, total birds counted and total bird species detected during the summer of 2002 and 2003 in the floodplain of the Colorado River in Mexico, presented by year and habitat type.

Total Total Bird Bird Total Total Total Survey Count Count Bird Species Species Total Sites 2002 2003 Count 2002 2003 Species Native Dry 31 1584 2019 3603 48 55 62 Native Wet 50 2871 3637 6508 86 74 97 Saltcedar Dry 50 1877 2593 4470 56 59 72 Saltcedar Wet 44 2130 2675 4805 84 70 93 Total 175 8462 10 924 19 386 106 92 120

Table 5. Average bird abundance and species richness per survey point observed during

the summer of 2002 and 2003 in the floodplain of the Colorado River in Mexico,

presented by year and habitat type. Standard errors are presented in parenthesis.

Abundance Abundance Average Richness Richness Average per point per point Abundance per point per point Richness 2002 2003 per point 2002 2003 per point Native 17.73 22.83 20.36 8.54 9.44 9.03 Dry (1.14) (1.35) (1.00) (0.40) (0.40) (0.31) Native 20.04 27.99 24.05 9.56 11.34 10.45 Wet (0.90) (1.06) (0.79) (0.31) (0.31) (0.24) Saltcedar 13.36 17.93 15.65 7.04 8.30 7.68 Dry (0.90) (1.06) (0.79) (0.31) (0.31) (0.24) Saltcedar 18.55 22.43 20.54 9.23 10.23 9.75 Wet (0.96) (1.13) (0.84) (0.33) (0.33) (0.26)

203

Table 6. Average richness, diversity and evenness indices for summer birds in the floodplain of the Colorado River Mexico during 2002 and 2003. Indices include total cumulative species during six summer visits, Hill’s N2 diversity index, N2/N1 evenness

measure, Shannon’s H’ diversity index and Pielou’s J measure of evenness. All indices were estimated by survey point. Standard errors are shown in parenthesis.

Total Cumulative Species per N2 Diversity H’ birds per N2/N1 point per point point Evenness J Evenness Native 0.72 Dry 21.16 (0.82) 9.40 (0.48) 2.54 (0.04) (0.01) 0.84 (0.006) Native 0.72 Wet 26.10 (0.64) 11.87 (0.38) 2.77 (0.03) (0.01) 0.85 (0.005) Saltcedar 0.75 Dry 18.42 (0.64) 8.96 (0.38) 2.46 (0.03) (0.01) 0.85 (0.005) Saltcedar 0.75 Wet 24.70 (0.68) 12.29 (0.40) 2.77 (0.03) (0.01) 0.87 (0.005)

204

Table 7. Pairwise differences of avian indices between habitat groups in the Colorado

River, Mexico, 2002-2003. P-values of Turkey-Kramer tests are shown in parenthesis.

Saltcedar Abundance Native Dry Native Wet Saltcedar Dry Wet Native Dry 0 Native Wet 3.7 (0.02) 0 Saltcedar Dry -4.7 (<0.01) -8.4 (< 0.01) 0 Saltcedar Wet 0.2 (.99) -3.5 (0.01) 4.9 (< 0.01) 0 Richness Native Dry 0 Native Wet 1.4 (<0.01) 0 Saltcedar Dry -1.3 (<0.01) -2.7 (< 0.01) 0 Saltcedar Wet 0.7 (0.29) -0.7 (0.21) 2.0 (<0.01) 0 Cumulative Species Native Dry 0 Native Wet 4.9 (< 0.01) 0 Saltcedar Dry -2.7 (0.04) -7.6 (< 0.01) 0 Saltcedar Wet 3.5 (<0.01) -1.4 (0.45) 6.3 (< 0.01) 0

N2 Native Dry 0 Native Wet 2.4 (< 0.01) 0 Saltcedar Dry -0.4 (0.89) -2.9 (< 0.01) 0 Saltcedar Wet 2.8 (< 0.01) 0.4 (0.88) 3.3 (< 0.01) 0 H’ birds Native Dry 0 Native Wet 0.2 (< 0.01) 0 Saltcedar Dry -0.07 (0.44) -0.3 (< 0.01) 0 Saltcedar Wet 0.2 (< 0.01) 0.003 (0.99) 0.3 (< 0.01) 0

N2/N1 evenness Native Dry 0 Native Wet 0.01 (0.99) 0 Saltcedar Dry 0.02 (0.29) 0.02 (0.32) 0 Saltcedar Wet 0.03 (0.32) 0.02 (0.37) 0 (0.99) 0 J Evenness Native Dry 0 Native Wet 0.01 (0.32) 0 Saltcedar Dry 0.01 (0.30) 0 (0.99) 0 Saltcedar Wet 0.03 (0.002) 0.02 (0.12) 0.02 (0.13) 0

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Table 8. Avian community similarity indices between habitat types for the floodplain of the Colorado River, Mexico, 2002-2003.

Species Species Observed Observed Shared First Second First Second Species Jaccard Morisita- Sample Sample Sample Sample Observed Index Horn

Native Native Dry Wet 62 97 59 0.59 0.94

Native Saltcedar Dry Dry 62 72 56 0.72 0.98

Native Saltcedar Dry Wet 62 93 56 0.57 0.87

Native Saltcedar Wet Dry 97 72 65 0.63 0.95

Native Saltcedar Wet Wet 97 93 74 0.64 0.97

Saltcedar Saltcedar Dry Wet 72 93 66 0.67 0.90

206

Table 9. Total detections, relative dominance, and ranking by habitat type of the summer avian community in the floodplain of the Colorado River, Mexico, 2002-2003. The four- letter code for the species is given in Table 1. ND = Native Dry, NW = Native Wet, SD =

Saltcedar Dry, Saltcedar Wet.

Total Rank Rank Rank Rank Relative Bird ND NW SD SW Total Rank ND NW SD SW Dominance MODO 735 1079 975 684 3473 1 1 1 1 1 17.91 VERD 340 444 431 322 1537 2 2 4 2 4 7.93 BHCO 263 508 348 368 1487 3 5 2 4 3 7.67 ABTO 315 405 385 303 1408 4 3 5 3 5 7.26 SOSP 99 452 191 374 1116 5 9 3 7 2 5.76 WWDO 304 386 255 162 1107 6 4 6 6 9 5.71 GAQU 203 300 302 192 997 7 8 7 5 8 5.14 WEKI 217 282 158 132 789 8 7 9 8 13 4.07 RWBL 223 245 151 138 757 9 6 10 9 12 3.90 COYE 48 285 105 231 669 10 16 8 13 6 3.45 BLGR 96 156 148 124 524 11 10 12 10 15 2.70 RNEP 85 136 115 140 476 12 11 14 11 11 2.46 GTGR 35 180 70 141 426 13 17 11 17 10 2.20 BNST 21 127 46 205 399 14 23 16 19 7 2.06 KILL 25 130 58 128 341 15 22 15 18 14 1.76 BTGN 68 71 107 57 303 16 12 20 12 19 1.56 CACW 51 95 71 50 267 17 15 17 16 21 1.38 MAWR 4 138 3 118 263 18 43 13 47 16 1.36 ATFL 54 62 86 32 234 19 14 22 14 25 1.21 LBWO 57 85 37 32 211 20 13 18 20 26 1.09 LENI 32 12 81 33 158 21 18 45 15 24 0.82 HOOR 32 73 31 18 154 22 19 19 21 37 0.79 SNEG 8 36 3 91 138 23 33 28 48 17 0.71 COMO 8 65 2 53 128 24 34 21 52 20 0.66 CRTH 17 46 22 24 109 25 26 24 24 30 0.56 WEME 29 37 21 11 98 26 21 27 25 48 0.51 BUOR 31 35 9 18 93 27 20 30 34 38 0.48 GREG 0 36 18 35 89 28 63 29 26 22 0.46 BLPH 17 46 2 20 85 29 27 25 53 35 0.44 YBCH 5 28 26 23 82 30 41 33 22 32 0.42 TUVU 18 46 5 4 73 31 24 23 41 60 0.38 GRHE 1 34 3 34 72 32 53 31 49 23 0.37 NOMO 17 21 11 23 72 33 28 34 30 33 0.37 CITE 0 3 1 65 69 34 64 66 66 18 0.36 WIFL 7 39 7 15 68 35 36 26 35 42 0.35 COGD 18 14 16 12 60 36 25 43 28 47 0.31 AMCO 1 30 1 27 59 37 54 32 59 28 0.30 GBHE 0 18 3 32 53 38 65 38 50 27 0.27 PSFL 10 19 13 11 53 39 31 35 29 49 0.27

207

GRRO 15 10 10 11 46 40 29 48 32 50 0.24 LEBI 1 18 0 26 45 41 55 37 73 29 0.23 NRWS 8 17 2 18 45 42 35 39 54 39 0.23 HOSP 7 1 26 10 44 43 37 88 23 51 0.23 BCNH 3 17 5 16 41 44 45 40 42 41 0.21 LOSH 6 4 17 12 39 45 38 61 27 46 0.20 TRES 6 8 4 19 37 46 39 52 44 36 0.19 PBGR 0 12 0 24 36 47 66 46 76 31 0.19 WESA 0 14 0 17 31 49 67 44 75 40 0.16 WAVI 1 10 7 13 31 48 56 49 36 44 0.16 VEFL 14 2 10 4 30 50 30 72 33 59 0.15 GRYE 0 6 1 22 29 52 68 56 62 34 0.15 GIWO 6 15 3 5 29 51 40 41 51 57 0.15 YWAR 0 11 10 7 28 53 69 47 31 53 0.14 CATE 0 9 0 15 24 55 70 51 77 43 0.12 BUOW 10 9 1 4 24 54 32 50 61 61 0.12 YHBL 2 19 1 2 24 56 49 36 60 72 0.12 CLSW 2 4 4 13 23 57 50 62 46 45 0.12 WIWA 5 6 5 6 22 58 42 54 43 56 0.11 CORA 3 5 7 2 17 60 46 58 37 69 0.09 CLRA 0 15 0 2 17 59 71 42 74 74 0.09 INDO 2 6 4 2 14 61 51 55 45 70 0.07 OSPR 3 5 1 2 11 62 47 59 63 73 0.06 TOWA 0 1 6 3 10 64 73 89 39 63 0.05 BEWR 0 2 7 1 10 63 72 76 38 76 0.05 RBGU 0 2 0 7 9 66 74 77 88 55 0.05 AMKE 4 5 0 0 9 65 44 57 79 100 0.05 FOTE 0 0 0 8 8 67 75 101 107 52 0.04 RODO 0 0 1 7 8 69 77 102 69 54 0.04 WTKI 3 3 1 1 8 70 48 64 64 78 0.04 MALL 0 7 0 1 8 68 76 53 78 81 0.04 WHIM 0 0 6 1 7 71 78 103 40 77 0.04 WETA 0 2 0 4 6 74 80 78 89 62 0.03 BHGR 0 5 0 1 6 72 79 60 80 82 0.03 LEGO 2 3 1 0 6 73 52 65 65 96 0.03 SPSA 0 0 0 5 5 78 83 105 108 58 0.03 HEWA 0 0 2 3 5 75 81 104 58 64 0.03 LESA 0 2 0 3 5 76 82 79 90 65 0.03 WEWP 1 0 2 2 5 79 58 98 57 71 0.03 OCWA 1 2 1 1 5 77 57 73 68 79 0.03 AMCR 0 2 2 0 4 80 84 80 55 94 0.02 BNOW 0 2 2 0 4 82 86 81 56 95 0.02 EUST 0 3 1 0 4 83 87 67 67 97 0.02 BCHU 0 4 0 0 4 81 85 63 81 101 0.02 GBTE 0 0 0 3 3 86 90 106 109 66 0.02 SBDO 0 0 0 3 3 89 92 107 110 67 0.02 VGSW 0 0 0 3 3 90 93 108 111 68 0.02 WFIB 0 2 0 1 3 91 94 82 91 83 0.02 BEVI 0 3 0 0 3 84 88 68 82 102 0.02 COHU 0 3 0 0 3 85 89 69 83 103 0.02 HOFI 0 3 0 0 3 87 91 70 84 104 0.02 YBCU 0 3 0 0 3 92 95 71 85 105 0.02 NAWA 1 2 0 0 3 88 59 74 86 106 0.02

208

YRWA 1 2 0 0 3 93 60 75 87 107 0.02 DCCO 0 0 0 2 2 98 100 109 112 75 0.01 LEYE 0 0 1 1 2 99 101 110 70 80 0.01 AWPE 0 1 0 1 2 95 97 90 97 84 0.01 CAEG 0 1 0 1 2 97 99 91 98 85 0.01 AMBI 0 2 0 0 2 94 96 83 92 108 0.01 BGGN 0 2 0 0 2 96 98 84 93 109 0.01 NOHA 0 2 0 0 2 100 102 85 94 110 0.01 RTHA 0 2 0 0 2 101 103 86 95 111 0.01 SEPL 0 2 0 0 2 102 104 87 96 112 0.01 CAGU 0 0 0 1 1 107 108 111 113 86 0.01 DEJU 0 0 0 1 1 109 110 113 114 87 0.01 EAGR 0 0 0 1 1 110 111 114 115 88 0.01 LISP 0 0 0 1 1 113 113 115 116 89 0.01 MAGO 0 0 0 1 1 114 114 116 117 90 0.01 SOSA 0 0 0 1 1 117 117 118 118 91 0.01 SWTH 0 0 0 1 1 118 118 119 119 92 0.01 WILL 0 0 0 1 1 119 119 120 120 93 0.01 COME 0 0 1 0 1 108 109 112 71 98 0.01 PEFA 0 0 1 0 1 115 115 117 72 99 0.01 ALHU 0 1 0 0 1 103 105 92 99 113 0.01 BRPE 0 1 0 0 1 105 106 93 100 114 0.01 BTYW 0 1 0 0 1 106 107 94 101 115 0.01 LBDO 0 1 0 0 1 112 112 95 102 116 0.01 REEG 0 1 0 0 1 116 116 96 103 117 0.01 WOST 0 1 0 0 1 120 120 97 104 118 0.01 BEKI 1 0 0 0 1 104 61 99 105 119 0.01 HOLA 1 0 0 0 1 111 62 100 106 120 0.01

209

Table 10. Relative dominance by habitat type of feeding guilds and residency status guilds of birds in the floodplain of the Colorado River, Mexico, 2002-2003.

Native Saltcedar Saltcedar Feeding Guild Native Dry Wet Dry Wet Aerial Piscivores 8.00 32.00 2.00 58.00 Divers 0.00 30.00 2.50 67.50 Dipping/Dabbling Foragers 3.41 39.77 1.52 55.30 Dense Vegetation Waders 2.82 48.59 4.52 44.07 Open Water Waders 2.84 32.62 8.51 56.03 Moist Soil Foragers 5.47 34.01 13.32 47.21 Flycatchers 24.05 32.09 24.12 19.74 Ground-Slash Foragers 20.71 31.96 26.17 21.16 Nectar Feeders 0.00 100.00 0.00 0.00 Predators on Vertebrates 28.15 27.41 23.70 20.74 Scavengers 24.66 63.01 6.85 5.48 Timber Drillers 26.25 41.67 16.67 15.42 Timber-Foliage Searchers 17.09 35.24 22.05 25.62 Residency Status Guild Breeding Landbirds 24.66 33.64 24.25 17.45 Breeding Waterbirds 0.00 8.33 1.39 90.28 Migratory Landbirds 10.51 38.85 21.34 29.30 Migratory Waterbirds 0.85 33.05 7.63 58.47 Resident Landbirds 19.16 33.15 24.45 23.24 Resident Waterbirds 4.85 37.70 9.56 47.88

210

Figure 1. Study area and survey sites in the floodplain of the Colorado River in Mexico.

Circles = Native Wet sites, squares = Native Dry sites, diamonds = Saltcedar Wet sites, and triangles = Saltcedar Dry sites. Large areas of the floodplain, particularly in the southern portion, does not have survey sites because these sections do not met the selection criteria, especially in terms of vegetation cover.

CA

Mexicali, Baja California

Map Area AZ

Mexicali Valley

San Luis Río Colorado, Sonora

Hardy River Colorado River

Ciénega de Santa Clara

Upper Gulf of California

211

Figure 2. Average bird abundance by habitat type in the floodplain of the Colorado River,

Mexico, 2002-2003. ND = Native Dry, NW = Native Wet, SD = Saltcedar Dry, SW =

Saltcedar Wet. Dots indicate values per point. Green diamonds indicate mean and 95% confidence intervals. Circles indicate probability values of the Turkey-Kramer tests.

Overlapping circles represent habitat types where the average bird abundance was not different.

212

Figure 3. Average bird species richness by habitat type in the floodplain of the Colorado

River, Mexico, 2002-2003. ND = Native Dry, NW = Native Wet, SD = Saltcedar Dry,

SW = Saltcedar Wet. Dots indicate values per point. Green diamonds indicate mean and

95% confidence intervals. Circles indicate probability values of the Turkey-Kramer tests.

Overlapping circles represent habitat types where the average bird abundance was not different.

213

Figure 4. Average Hill’s N2 avian diversity by habitat type in the floodplain of the

Colorado River, Mexico, 2002-2003. ND = Native Dry, NW = Native Wet, SD =

Saltcedar Dry, SW = Saltcedar Wet. Dots indicate values per point. Green diamonds

indicate mean and 95% confidence intervals. Circles indicate probability values of the

Turkey-Kramer tests. Overlapping circles represent habitat types where the average bird abundance was not different.

214

Figure 5. Average Shannon’s H’ avian diversity by habitat type in the floodplain of the

Colorado River, Mexico, 2002-2003. ND = Native Dry, NW = Native Wet, SD =

Saltcedar Dry, SW = Saltcedar Wet. Dots indicate values per point. Green diamonds indicate mean and 95% confidence intervals. Circles indicate probability values of the

Turkey-Kramer tests. Overlapping circles represent habitat types where the average bird abundance was not different.

215

Figure 6. Canonical correspondence analysis ordination diagram of avian residency status guilds against environmental variables. The red arrows represent environmental gradients from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D) dominated sites. The distance between the guilds approximates the dissimilarity of distribution of relative abundance of those guilds across the survey sites. The position of the guilds in relation to the environmental gradients is an estimation of the optimum abundance of the guild in respect to values of the environmental gradient.

216

Figure 7. Canonical correspondence analysis ordination diagram of avian feeding guilds against environmental variables. The red arrows represent environmental gradients from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D) dominated sites. The distance between the feeding guilds approximates the dissimilarity of distribution of relative abundance of those guilds across the survey sites. The position of the feeding guilds in relation to the environmental gradients is an estimation of the optimum abundance of the guild in respect to values of the environmental gradient.

217

Figure 8. Canonical correspondence analysis ordination diagram of the 25 most common species during the study (>90 % of all detections). The red arrows represent environmental gradients from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D) dominated sites. The distance between species approximates the dissimilarity of distribution of relative abundance of those species across the survey sites.

The position of the species in relation to the environmental gradients is an estimation of the optimum abundance of that species in respect to values of the environmental gradient.

218

Figure 9. Ordination diagram of species richness (cumulative species per point) in relation to vegetation type and surface water. The red arrows represent environmental gradients from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D) dominated sites. The distribution of the contour plot of richness values summarizes a multivariate general linear model regression of the cumulative species richness by survey site against the environmental variables.

219

Figure 10. Ordination diagram of Hill’s N2 avian diversity index per point in relation to

vegetation type and surface water. The red arrows represent environmental gradients

from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D)

dominated sites. The distribution of the contour plot of N2 diversity values summarizes a

multivariate general linear model regression of avian diversity by survey site against the

environmental variables.

220

Figure 11. Ordination diagram of bird cumulative abundance per point in relation to vegetation type and surface water. The red arrows represent environmental gradients from saltcedar (S) toward native (N) dominated sites, and from wet (W) towards dry (D) dominated sites. The distribution of the contour plot of abundance values summarizes a multivariate general linear model regression of avian abundance by survey site against the environmental variables.

221

Figure 12. Possible paths in which surface water enhances avian richness and abundance in riparian areas. The arrows indicate the possible direction of causality.

222

APPENDIX D

STRATEGIES FOR THE CONSERVATION OF BIRDS IN THE COLORADO RIVER

DELTA, MEXICO

Manuscript prepared for submission to the journal The Condor

223

Bird Conservation in the Colorado River Delta

STRATEGIES FOR THE CONSERVATION OF BIRDS IN THE COLORADO RIVER

DELTA, MEXICO

Osvel Hinojosa-Huerta1,2

Helena Iturribarría-Rojas2

Yamilett Carrillo-Guerrero1,2

William W. Shaw3

Carlos Valdés-Casillas1,2

1104 Biological Sciences East

School of Natural Resources, University of Arizona

Tucson, AZ 85721

e-mail: [email protected]

2Pronatura Noroeste, Avenida Jalisco 903,

San Luis Río Colorado, Sonora, México. 83440.

3225 Biological Sciences East

School of Natural Resources, University of Arizona

Tucson, AZ 85721

224

Abstract. We developed strategies for the conservation of birds in the Colorado River delta. Major goals include protecting all bird species, recovering species at risk, maintaining common birds, and basing all actions on collaborative, voluntary efforts. We selected seven conservation targets, which included 56 focal species: Marshbirds,

Colonial Waterbirds, Riparian Birds, Migratory Landbirds, Migratory Waterbirds,

Saltgrass Bird Community, and Marine Zone Bird Community. The criteria for the selection of conservation targets and focal species included their population and habitat status, current threats, endemism, considerations to cover a wide range of ecological requirements, and considerations to develop effective biological indicators of the system’s health. Analysis of the focal species revealed that: 1) availability of fresh water is the major requirement for the recovery and conservation of birds in the delta, 2) loss of habitat structure and size has extirpated or greatly reduced breeding populations of several bird species, and 3) recent floods and restoration efforts have recovered part of the wetland areas, increasing the populations of threatened or endangered species. We identified eight lines of action for implementation: 1) collaborate with the Upper Gulf of

California and Colorado River Delta Biosphere Reserve, 2) legally protect the Colorado

River floodplain, 3) develop a Management Plan with the National Water Commission for the floodplain of the Colorado River, 4) acquire water rights to secure flows to the wetland areas, 5) expand the community-based conservation projects, 6) implement restoration projects, 7) develop a program of environmental education, and 8) develop an outreach and communications program.

Key words: instream flows, pulse floods, riparian, wetlands

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INTRODUCTION

The process of defining conservation priorities has become a critical requirement to achieve recovery objectives for many bird species and their habitats (Dunn et al. 1999,

Carter et al. 2000). This need has become evident as bird populations across North

America have suffered population declines over the last century (Kushlan et al. 2002,

Rich et al. 2003). These declines are related to the dramatic rate at which habitat has been destroyed, diminishing the area and quality of breeding grounds, wintering areas, and migratory stopover sites (Weller 1988, North American Bird Conservation Initiative

2000).

Wetland and riparian areas have been more susceptible to the effects of increased human activities (National Research Council 1995). In western North America, the patterns of degradation are significant: wetland loss in the California Central Valley is estimated at

95% (Zedler 1988), and loss along the U.S. Pacific coast has been 50% (Helmers 1992).

This trend has been particularly critical in the Sonoran Desert, where the allocation of water for human uses has dried up most of the riparian forests and wetlands (Brown

1985). The Lower Colorado River is a clear example, as its delta has lost more than 80% of wetland area over the last 80 years (Valdés-Casillas et al. 1998).

Worldwide, loss of wetland and riparian areas is often related to water management practices (Lemly et al. 2000), and this certainly is the case in the Colorado Basin (Lemly

1994, Morrison et al. 1996), where water diversions for human activities have negatively impacted the delta region (Glenn et al. 1996). Nevertheless, agricultural runoff, sporadic flood flows, and their interaction with the tidal regime from the Upper Gulf of California

226 have restored and maintained part of these wetlands, showing that environmentally sound water management could help restore and conserve some avian habitats (Glenn et al.

2001, Zamora-Arroyo et al. 2001).

The interest in restoring the Colorado River delta has been increasing on both sides of the border (Valdés-Casillas et al. 1998, Pitt 2001). Opportunities for restoration have been identified (Briggs and Cornelius 1998, Luecke et al. 1999, Glenn et al. 2001) and these ideas have been discussed in public forums incorporating environmental considerations into the political, social, and economic framework (Varady et al. 2001).

The process has resulted in a binational consensus among stakeholders, agencies, environmental groups, and academia on the importance of developing and implementing a binational conservation/restoration program, based on scientific information, which would consider water requirements for wildlife conservation. These concepts were the basis for the development of the strategies for the conservation of birds in the Colorado

River delta, which is only the next step in this long-term process to ensure the permanence of birds and their habitats in this region.

The strategies were developed under an existing framework of institutions working toward the conservation of the delta ecosystem, optimizing the existing constituency among government agencies and stakeholders. The overall vision was to establish criteria for the long-term conservation of avian communities in the Colorado River delta, that could: 1) recover populations of birds that have been extirpated or are in very reduced numbers, 2) maintain the populations of common birds, and 3) maintain the ecological integrity of the system that provides functions and services to a diversity of life. The

227 process included an analysis and generation of scientific information, the analysis of threats, the definition of conservation goals, and the definition of management guidelines.

An extended version of this publication has been prepared as a Bird Conservation Plan for the Colorado River Delta.

The Colorado River Delta

The Colorado River delta covers 169,000 ha and supports an array of contrasting ecozones, ranging from the harsh desert to the productive wetlands (Fig.1). The major ecozones in the Colorado River delta considered in these strategies are: the Colorado

River floodplain, the wetlands of the Hardy River, off-channel wetlands, the intertidal and marine zone, and agricultural areas (Fig.1, Table 2).

Between 1993 and 2003, 358 bird species have been detected in the Colorado delta

(Patten et al. 2001, Hinojosa-Huerta et al. 2006). The delta provides habitat for migratory and wintering waterbirds and for neotropical migrant landbirds (García-Hernández et al.

2001, Mellink and Ferreira-Bartrina 2000). Nearly 200,000 shorebirds and 60,000 ducks and geese use the delta wetlands as wintering grounds or for stopover habitat during migration (Morrison et al. 1992, Mellink et al. 1997), and at least 110 species of neotropical migratory landbirds visit the delta during their migratory movements (Patten et al. 2001).

The delta ecosystem has long been recognized as one of the richest regions for wildlife in the southwestern United States and northwestern México (Sykes 1937, Leopold 1953,

Glenn et al. 2001). Prior to the dam era, cottonwood (Populus fremontii) – willow (Salix

228 gooddingii) forest was very common in the region, extending over tens of thousands of hectares throughout the Mexicali Valley (Sykes 1937). Mesquite bosque (Prosopis pubescens and P. glandulosa) dominated the upland terraces, in association with arroweed (Pluchea sericea) and quail bush (Atriplex lentiformis; Mearns 1907). Oxbows, backwaters, and seepage were common, and provided for vast extensions of marshlands

(Sykes 1937).

Eighty years later, only 3,000 ha of cottonwood-willow remain, regenerated after pulse floods reached the delta, and maintained with “administrative losses” from the irrigation systems (Glenn et al. 2001). The extent of mesquite bosque has been largely diminished, as upland areas have been cleared for agriculture development (Valdés-Casillas et al.1998). Marshlands have been reduced as well, although in a lesser extent (Glenn et al.

1996).

As in other delta ecosystems worldwide, insufficient and unreliable water supplies and poor water quality are the ultimate causes of environmental degradation in the Colorado

River delta, intensified in this particular case by location in an arid ecoregion.

The use of the river’s water is governed by a complex set of legal and administrative agreements known collectively as the Law of the River (Luecke et al. 1999). This group of agreements gives the lowest priority to uses such as maintaining a flow in the river to support plants, fish, and wildlife, and it does not consider water allocation to maintain the delta’s ecological health in the Mexican side of the river.

Lower basin states in the U.S. are now using their full entitlement of water from the river and are working to secure access to additional supplies (Cornelius et al. 2004). The

229 environment in the Mexican portion of the Colorado River does not have an allocation of water, and thus is maintained with unintended water releases from dams and irrigation systems upstream (Zamora-Arroyo et al. 2001). In the United States, criteria for retaining surplus water for human use are being revised. Currently, little or no water reaches the

Gulf of California.

Most of the present delta vegetation has been enhanced and maintained by flood releases over the last 20 years (Glenn et al. 1996), restoring in part the willow-cottonwood stands.

However, lack of yearly flooding regime inhibits riverbank salt washing and augments the tidal influence, causing soil salinity to increase. This allows invasive exotic plants, such as saltcedar (Tamarix ramosissima), to colonize vast areas.

The ecological deterioration in the delta has significantly impacted the local avifauna.

Ten species of breeding birds and 14 species that use this area as stopover or wintering ground have required a status of legal protection under Mexican laws (Diario Oficial de la Federación [DOF] 2002; Table 1).

Populations of many species have declined regionally, and some have been extirpated locally, including populations of five breeding and two wintering species (Hinojosa-

Huerta et al.2006; Table 1). Most affected have been riparian-obligate breeders, waterfowl, and some marshbirds. Despite these changes, the delta still maintains an abundant and diverse avifauna (Hinojosa-Huerta et al. unpublished [a]). Its importance for the conservation of birds has been recognized both nationally and internationally (see

Zamora-Arroyo et al. 2005).

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METHODOLOGY

The major components in the process of defining the conservation strategies included: 1)

compilation of existing information, 2) analysis of information gaps, 3) data collection, 4) analysis of the information, 5) definition of conservation targets and management recommendations, and 6) definition of recommendations for implementation.

Compilation of Information

This component included the compilation and analysis of geographic material, scientific papers, gray literature, field notes, and information from personal interviews with biologists and residents. This yielded a collection of over 100 papers related to birds and their conservation in the Colorado River delta.

All of the reviewed material contributed to a better understanding of the delta system, but

several of these papers were essential for the definition of the status of birds or as a

baseline of the historic avifauna of the delta. These include the work of Grinnell (1928),

Rosenberg et al. (1991), Russell and Monson (1998), Ruiz-Campos and Rodríguez-Meraz

(1997), and Patten et al. (2001), as well as the numerous papers published by Eric

Mellink, Eduardo Palacios, and collaborators (Palacios and Mellink 1992, 1993, 1996;

Mellink and Rea 1994, Peresbarbosa and Mellink 1994, 2001; Mellink et al. 1996, 1997,

2002; Mellink and Ferreira-Bartrina 2000; Palacios et al. 2000). In terms of changes in the landscape and vegetation, important benchmarks were the work of Sykes (1937) and

Glenn et al. (1996, 2001).

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Recent avian research has also provided much of the basis for the development of the strategies, including information on the populations of protected species (García-

Hernández et al. 2001, Hinojosa-Huerta et al. 2001a, 2001b, Hinojosa-Huerta et al.

2004), a review of the status and changes in the avifauna of the region (Hinojosa-Huerta et al. 2006), an analysis of the spatial and temporal patterns of birds use and their habitat relationships in the riparian areas (Hinojosa-Huerta et al. unpublished[a]), information on the patterns of relative abundance, species composition, temporal presence and habitat use of migrant landbirds through the region (Hinojosa-Huerta et al. 2005), and the effect of water changes and saltcedar on riparian birds (Hinojosa-Huerta et al. unpublished [b]).

On the other hand, recent information on vegetation and wetlands has also improved the definition of strategies, including a review on the status and priorization of wetland areas in the Colorado River delta (Zamora-Arroyo et al. 2005), an analysis of the regeneration processes of native riparian vegetation and its relationship with saltcedar (Nagler et al.

2005) and an analysis of the ecophysiology of native trees and saltcedar (Glenn and

Nagler 2005).

Definition of Conservation Targets, Focal Species, and Management Recommendations

We selected bird conservation targets in order to define the management recommendations for the conservation of birds and their habitats. The targets were defined as bird groups with similar habitat requirements, thus sharing similar pressures and needs. In the process we applied the guild concept, in order to identify and manage the capability of habitat zones to support bird populations (Verner 1984, Block et al.

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1987). Besides a complete list of species within each group, we also defined focal species within each target, in order to further refine the habitat management implications and facilitate monitoring and evaluation efforts.

A preliminary list of conservation targets was prepared, based on existing information of the status of birds and habitat types in the Colorado River delta. Emphasis was placed on bird groups whose habitats have deteriorated in the delta, and which included endangered and threatened species or whose populations in the region have declined drastically. Bird groups with species whose breeding populations have been extirpated and might be recovered with restoration efforts were also considered.

A list of focal species was selected for each group, considering the most representative birds which might cover the habitat needs of all the species within the group, and function as indicators in monitoring efforts (Szaro 1986, Croonquist and Brooks 1991).

Focal birds also included key species within the delta ecosystem, as well as endemics and those that require special attention due their status (endangered or threatened).

The preliminary list was analyzed and discussed by an expert panel to define a final list of targets and species. This process was part of the Workshop to Identify Conservation

Priorities in the Colorado River Delta, held in Tijuana, Baja California on October 14-17,

2002 (Zamora-Arroyo et al. 2005). The panel included expertise in different topics of ornithology and bird conservation (see Appendix A for list of participants). The discussions and final selections were based on the purpose of guiding conservation and restoration efforts in the Colorado River delta, and providing insight of the role of the delta ecosystem at the regional and hemispheric scales.

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The analysis was continued to the selection of a network of priority sites in the Colorado

River delta that, with proper management, could ensure the long-term persistence of the delta avifauna, including rare and common species, their habitats, and the ecological processes that maintains the integrity of the ecosystem.

This analysis also yielded the following products: 1) restoration potential of priority conservation sites, 2) assessment of the quantity, quality, and timing of water flows required to support each of the identified sites and habitat types, and 3) a state-of- knowledge and gap analysis identifying priority research needs and resources required to implement them. This information was integrated in the management recommendations for each of the conservation targets.

Finally, all this information was put together in a draft document, that was further reviewed by the participants in the workshop, as well as by staff from government agencies, NGO’s, and academic institutions involved in the restoration of the Colorado

River delta (Appendix A).

CONSERVATION TARGETS AND FOCAL SPECIES

The conservation targets are the centerpiece of the strategies, as they set the guidelines

for the definition of conservation priorities. The focal species help to provide the details

for the management recommendations.

Seven bird groups were included in the list of conservation targets, with a selection of 56

focal species, covering a wide range of habitat requirements (Table 3). The final list of

targets include: 1) marshbirds, 2) colonial waterbirds, 3) riparian birds, 4) migratory

234 landbirds, 5) migratory waterbirds, 6) saltgrass bird community, and 7) marine zone bird community

Marshbirds

This conservation target included species from two families: Rallidae and Ardeidae

(Table 3). These birds strongly depend upon the emergent vegetation of freshwater and brackish marshes. The focal species for this conservation target are: Yuma Clapper Rail,

California Black Rail (Laterallus jamaicensis coturniculus), Least Bittern (Ixobrychus exilis), and Virginia Rail (Rallus limicola).

The overall goal for this target is maintaining a dynamic system of marsh areas in the

Colorado River delta that secures the preservation of these birds. Specific goals include conserving existing marshlands (Ciénega de Santa Clara and El Doctor), restore or enhance degraded areas (Hardy and Colorado rivers), limit the expansion of saltcedar, and protect the marshes from cattle.

From these species, the Yuma Clapper Rail is endemic to the Lower Colorado River and its delta, and is listed as Endangered in the U.S. and Threatened in México (Eddleman and Conway 1998, DOF 2002). The California Black Rail is listed as Endangered in

México and in California, and is a candidate species to be listed in the United States

(California Department of Fish and Game 1999, DOF 2002).

Populations of marshbirds have declined in North America during the last decades

(Eddleman et al. 1988). This has been the case in the delta, where much habitat has been lost or degraded. Nevertheless, the status of marshbirds in the delta is in fairly good

235 condition, especially due to the existence of the Ciénega de Santa Clara and El Doctor wetlands, which together provide about 6,300 ha of habitat for these birds. In particular, the Ciénega maintains about 70% of the total population of the Yuma Clapper Rail, with a population estimate of 4,850 individuals in 2003 (Hinojosa-Huerta 2003). On the other hand, the California Black Rail is very reduced in numbers, with an estimate of less than

50 pairs in the delta (Hinojosa-Huerta et al. 2001b, 2003). The contrast is based on the specific habitat requirements of the two species: while the Clapper Rail inhabits cattail stands, with brackish water (3-8 ppt of salinity), and variable water depths (0-70 cm;

Eddleman 1989), the Black Rail prefers bulrush stands, with freshwater (0-3.5 ppt of salinity), and very shallow (<5 cm) and stable water levels (Flores and Eddleman 1995).

The drastic difference in status between these two marshbirds is a good example of the importance of maintaining a diversity of marsh habitat types, and in monitoring several focal species in order to secure the preservation of the diversity of bird life.

The maintenance of dynamism in the marshes and management to maintain stands of emergent vegetation of different ages is one of the major conservation actions for this target. This is critical in particular for the preservation of Yuma Clapper Rails. Between

1999 and 2002, the species had a population decline of 52% (Hinojosa-Huerta et al.

2003). This trend was related to the senescence of cattail stands in the Ciénega de Santa

Clara. From 2002 to 2003, fluctuations in the direction of water flows created patches of mixed ages of cattails. During the breeding season of 2003, the Clapper Rail counts increased 40%, compared with counts in 2001 and 2002.

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Restoration is also a critical part of the conservation of marshbirds, in particular for the expansion of available habitat in the Colorado River delta. Current projects have shown that restoration is feasible. In the main stem of the Colorado River, marshes have regenerated in response to instream flows. These marshes were soon colonized by

Clapper Rails, Black Rails, Virginia Rails, and Least Bitterns. In the Hardy River, community projects have restored about 40 ha of marshes, which has resulted in a four- fold increase in the density of Yuma Clapper Rails there (Hinojosa-Huerta et al. in press[a]).

Management Recommendations for Marshbirds

• Secure water for the Ciénega de Santa Clara, at least at current flow and quality.

• Maintain salinity levels of water sources for marshlands at 3.2 ppt or preferably lower.

• Exclude cattle from El Doctor and the eastern side of the Ciénega de Santa Clara.

• Limit groundwater extractions in the San Luis Mesa and nearby El Doctor, to protect the water sources for these wetlands.

• Manage cattail stands to avoid marsh senescence in the Ciénega (>6 or 7 years old), with water flows, controlled fires, or clearing vegetation.

• Enhance marshes in the Hardy River: 1) by managing agricultural runoff with dikes, to flood a larger area in the floodplain, and 2) by increasing the water flow through the

Hardy River.

• Enhance marshes in the Colorado River, by maintaining a constant instream flow and restoring water access to backwaters and secondary streams.

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• Optimize the potential for marsh maintenance with agricultural drainage water, especially at Laguna del Indio and the eastern drains of the Mexicali Valley, by avoiding extended periods of desiccation and avoiding extreme fluctuations in water flows and salinity.

Information Needs for Marshbirds

• Determine population trends.

• Evaluate the risk of contaminants.

• Evaluate the effect of restoration and management activities on the populations of marshbirds.

• Determine the exact sources of groundwater maintaining El Doctor wetlands, and the effect of groundwater pumping at the San Luis Mesa on these wetlands.

• Determine the groundwater dynamics that maintain the Andrade Mesa wetlands, evaluate the potential effects of lining the All-American Canal, and identify alternatives to protect these wetlands.

Nesting Waterbirds

This conservation target included the waterbird species that breed in aggregations

(colonies or semi-colonies) in the Colorado River delta. This included 14 species from three families: Ardeidae, Charadriidae, and Laridae. Major breeding sites for these birds are Montague Island, Cerro Prieto ponds, and the saltflats of El Doctor and Ciénega de

Santa Clara (Mellink et al. 1996, Molina and Garrett 2001, Peresbarbosa and Mellink

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2001). There are also important heronries at some drains in the Mexicali Valley (Mellink et al. 2002). The focal species for this target are: Snowy Egret (Egretta thula), Snowy

Plover (Charadrius alexandrinus), Gull-billed Tern (Sterna nilotica), and Black Skimmer

(Rhynchops niger; Table 3).

The goal for the conservation target is to maintain suitable nesting, roosting, and foraging sites for these species in the Colorado River delta. One of the major conservation objectives is to protect the highly localized aggregation sites, and protect the colonies from predators and human disturbance.

The breeding waterbirds of the Colorado River delta are fairly well known, in particular their status and relative abundance (Patten et al. 2001, Peresbarbosa and Mellink 2001).

Yet, there is little information on their population dynamics and trends, which are critical to effectively protect these birds. Equally important is determining the factors influencing their productivity and survivorship, which is necessary to adequately amend any activities harming them.

Aquatic habitat types in the delta have been decimated, and populations of waterbirds have been reduced accordingly. However many species, including most herons and egrets, are still common or fairly common, as large wetland areas have been maintained.

Other species are not as common, and require specific conservation measures.

Populations of the western subspecies of the Gull-billed Tern appear to be declining, and the species is under consideration to be listed as Endangered in the United States (Parnell et al. 1995). The Least Tern (Sterna antillarum) is under Special Protection in México, as its populations have been reduced across the Gulf of California (Palacios and Mellink

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1996). Western populations of Snowy Plovers have also declined drastically, and the subspecies is listed as Threatened in México and Endangered in the United States (Powell

1998, DOF 2002). The Reddish Egret (Egretta rufescens) is a rare breeder in the delta, with just a few pairs (Mellink et al. 2002), and is under Special Protection in México

(DOF 2002).

Management Recommendations for Nesting Waterbirds

• Continue the protection of Montague Island as the core zone of the Biosphere Reserve, restricting human disturbance during the breeding season.

• Exclude cattle from nesting sites at El Doctor and Ciénega de Santa Clara.

• Protect and secure the permanence of the sediment islands at the evaporation ponds of

Cerro Prieto where waterbirds nest; restrict human disturbance during breeding season.

• Protect the heronries in the Mexicali Valley (Hardy River, Ejido Cucapá Indígena, and

Ejido Oaxaca) from human disturbance and destruction.

• Protect and enhance wetland areas that provide foraging, roosting, and dispersal sites for the waterbirds in the Colorado River delta.

Information needs for Nesting Waterbirds

• Determine population trends.

• Determine the major factors affecting productivity and survivorship.

• Determine the effect of lack of freshwater on the breeding success and abundance of waterbirds at the intertidal and marine zones of the Colorado River delta.

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• Determine if artificial nesting platforms or mounds could improve breeding success of waterbirds at Montague Island.

• Determine if increasing the amount of available sediment islands at Cerro Prieto could improve productivity and population numbers of waterbirds.

• Evaluate the risk of contaminants on the populations of waterbirds.

• Evaluate the effect and value of agricultural areas on the populations of waterbirds.

Riparian Birds

This conservation target included the birds that breed in the riparian areas, with a special emphasis on those species that are riparian-obligate nesters. The selected species encompass a wide variety of habitat types, from mature cottonwood-willow forests, to mesquite woodlands, and young stands of colonizing willow, seep willow, and arroweed.

The purpose of this selection was to provide the basis to restore and maintain a diverse and ecologically functional riparian system in the delta.

The goal for this target is to protect the habitat of these birds: in particular the cottonwood and willow forests, but also the mesquite woodlands that occupy the terraces in the floodplain. It is important to maintain foliage diversity and species heterogeneity in the floodplain of the Colorado River, as well as the maintenance of both connectivity and large blocks of habitat. The target area includes the floodplain of the river delimited by the levee system that traverses the Mexicali Valley, starting in the north at Morelos Dam, and extending down to the confluence of the Hardy and Colorado Rivers.

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Focal species for this target include 11 birds from 8 families (Table 3). This list includes species that were common breeding residents in the Colorado River in México, but that are now extirpated, such as the Southwestern Willow Flycatcher (Empidonax traillii extimus) and the Fulvous Whistling Duck (Dendrocygna bicolor). It also includes some species that are now rare or occasional breeders in this region, such as Yellow-billed

Cuckoos (Coccyzus americanus). In the list are also species that have returned or have increased their numbers in response to revegetation of the floodplain, and some species that have remained common, but that their population fluctuations indicate the health of the system.

One species, the Brown-headed Cowbird, was included in the group in order to track disturbances in the floodplain and any impacts this species might cause on other riparian birds.

Brown-headed Cowbirds have expanded their range and increased their populations in western North America in relation to increased human activities. Along riparian areas of the Sonoran Desert, habitat fragmentation and intensified farming practices have increased the nest parasitism success of cowbirds, causing population declines in riparian-dependant songbirds, such as Willow Flycatchers and Bell’s Vireos (Vireo bellii;

Sogge et al. 1997, Averill-Murray et al. 1999, Powell and Steidl 2000).

The group of riparian birds is the conservation target with the least information available about them. The status of many of these species is just being determined, and for some is still unclear. As with other targets, there is no information on population trends, productivity, survivorship, and the factors influencing these parameters.

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On the other hand, this is the conservation target that has probably been under higher pressure, as riparian areas were almost non-existent for several decades in the delta, and these systems require freshwater as a source, one of the most rare commodities on the region. Furthermore, this stretch of the Colorado River lies outside the limits of the

Biosphere Reserve, and thus does not have any protection. A similar situation occurs for its species: while it is the target with the highest number of extirpated species (6 extirpated; 3 in very reduced numbers), there are no riparian birds that breed or used to breed in the delta that have legal protection in México, and only one is listed in the

United States (the Southwestern Willow Flycatcher).

Yet, the conservation and restoration opportunities are enormous. After almost 20 years of continuous desiccation (1960-1979), the floodplain has been revegetated in response to pulse floods that occurred during 1983-1986, 1993-1994 and 1997-1999 and a modest but continuous instream flow during the last 3 years. Near 3,000 ha of cottonwood-willow association have been reestablished in the 20,000 ha floodplain, and now there are numerous breeding species that are common in the floodplain, including Abert’s

Towhees (Pipilo aberti), Song Sparrows (Melospiza melodia), Crissal Thrashers

(Toxostoma crissale), Ash-throated Flycatchers (Myiarchus cinerascens), and Bullock’s

Orioles (Icterus bullockii). Some species have reestablished in the area recently in response to the revegetation, and now are uncommon, but regular breeders, including

Ospreys (Pandion haliaeetus), Vermillion Flycatchers (Pyrocephalus rubinus), Yellow- breasted Chats (Icteria virens), and Lesser Goldfinches (Carduelis psaltria). This shows that proper management can reestablish the functions of the riparian corridor, and

243 hopefully, with the adequate conservation measures, the extirpated species might return to the delta.

A 15-year drought is expected for the Colorado River basin, which would mean an extended desiccation again of the Colorado floodplain in México. This would cause the loss of the restored cottonwood-willow areas, and an impact for the avifauna regionally.

Therefore, is now even more critical to implement conservation measures to protect the riparian corridor of the Colorado delta.

Management Recommendations for Riparian Birds

• Designate the floodplain of the Colorado River in México under a protection category within the National System of Protected Areas (SINANP).

• Allocate a continuous instream flow (2-3 m3/s) and a larger pulse flood every 4 or 5

years (100 m3/s) to facilitate the propagation of new trees and maintain the floodplain dynamics.

• Limit management practices in the floodplain that damages riparian vegetation, including vegetation clearings, river canalization, and blocking of secondary streams and

backwaters.

• Control human induced fires in the floodplain.

• Restrict groundwater pumping within 100 m of the floodplain.

• Limit logging and collection of fire wood in the floodplain.

• Control solid waste in and around the floodplain.

• Restore mesquite terraces.

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• Enhance and protect priority sites

• Control sediments that build up on the main stem and block secondary streams.

Information Needs for Riparian Birds

• Clarify the status of Fulvous Whistling Duck, Western Screech Owl (Otus kennicottii),

Gilded Flicker (Colaptes chrysoides), Willow Flycatcher, Bell’s Vireo, Lucy’s Warbler

(Vermivora luciae), Yellow Warbler (Dendroica petechia), and Summer Tanager

(Piranga rubra).

• Determine the abundance of the breeding population of the focal species, in particular.

• Determine population trends.

• Determine breeding success, productivity, and survivorship; and the factors influencing them.

• Determine the response of the avian community to long-term restoration and water flows.

• Determine the effect of fire on the riparian birds.

• Evaluate the impacts of cattle (goats) grazing in the floodplain.

Migratory Landbirds

This conservation target included the species of landbirds that breed in the United States and Canada, winter in southern México and Central America, and for which the delta is an important stopover site during their migration. The goal for this target is to maintain a continuous mosaic of riparian corridors, desert shrubs, and microphyll woodlands that are

245 used by these birds during their spring migration, across the Gran Desierto, Upper Gulf

Region, and Colorado River delta. This goal also benefits fall migrants and wintering species. Many of the migratory landbirds are also benefited by the goals and management recommendations for the riparian birds.

The focal species of this target include 6 birds from 6 families (Table 3). Likewise riparian birds, this selection included a variety of birds to encompass different habitat requirements. However, emphasis was made on the most common migrants, in order to have a sufficient sample size during monitoring efforts to yield significant results on their trends and survivorship.

The status as migrants of many of these birds is fairly well known, in particular the species composition, their relative abundance, distribution, and seasonality. The detailed studies and accounts of birds conducted on nearby areas, such as the Salton Sea and the

Lower Colorado River (Rosenberg et al. 1991, Patten et al. 2001) have also provided solid background on the status as migrants of many of these species. However, there are no long-term data, and the effects of the changes in the delta on these species is unclear, as historical records do not provide a detailed baseline of the status of the migrant landbirds previous to the construction of dams.

It is likely that the habitat degradation and loss in the Colorado River delta was one of the many factors causing declines in populations of many of these birds, as the quality of stopover sites in migration routes has been identified as one of the most critical parameters defining the status and population trends of neotropical migratory landbirds

(Hutto 2000).

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This is particularly important in this region, as migratory landbirds have to fly along the coast of Sonora on their northbound migration, with the Gulf of California on one side, and the open desert on the other. A critical stopover site in this journey is El Doctor.

These wetlands are the only large patch of vegetation (>1 ha) in at least 150 miles to the south, east, and west. As such, El Doctor is a concentration spot funneling migratory landbirds north along the coast of Sonora, by providing much needed cover, freshwater, and food.

Thousands of migratory landbirds from over 80 species concentrate every spring at El

Doctor, showing the importance of the desert oases as stopover sites. Many of these birds continue north following the corridor of the Colorado River, while others move west, migrating through central and coastal California.

The species of migratory landbirds moving through the delta are not protected in México.

However, El Doctor is included in the core zone of the Biosphere Reserve, bringing protection to one of the most important sites. This type of protection should also be granted to other important stopover sites north and south of El Doctor, such as the

Colorado River.

Management Recommendations for Migratory Landbirds

• Protect critical stopover sites, either by a designation status or by means of other conservation tools, such as conservation easements.

• Maintain migration corridors along the coast with “stepping stones” stopover sites, and along the natural corridors of the Colorado, Hardy, and Sonoyta Rivers.

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• Exclude cattle from El Doctor.

• Limit groundwater extractions that could impact stopover sites, in particular in desert areas, such as El Doctor and Río Sonoyta.

• Restore critical stopover areas with native trees, in particular honey and screwbean mesquite.

Information Needs for Migratory Landbirds

• Determine the trends of landbirds migrating through the delta.

• Determine stopover length, weight changes, survivorship and habitat preferences.

• Determine breeding and wintering sites of birds that migrate through the delta.

• Determine how habitat degradation and restoration efforts affect en route survivorship, overall survivorship, productivity, and population numbers of these birds.

Saltgrass Avian Community

This conservation target included the birds that depend upon or that commonly use the saltgrass areas of the delta, in particular the endemic Palmer’s saltgrass. This grass covers the banks of the river near its confluence with the Upper Gulf and an important area of

Montague Island (Glenn et al. 2001). The goal is to maintain the remnant areas of this saltgrass in the delta.

A wide variety of birds use this area, providing food and nesting material where no other vegetation grows. Birds in this area include geese, ducks, shorebirds, herons and egrets,

248 gulls and terns, and the Large-billed Savannah Sparrow (Passerculus sandwichensis rostratus), endemic to this region, an obligate resident of the saltgrass areas, and a bird under Special Protection in México (DOF 2002). This sparrow was selected as the only focal species for this conservation target, as its conservation secures the preservation of the saltgrass areas for the benefit of other wildlife.

The Palmer’s saltgrass can live with saltwater, but it requires freshwater to reproduce and germinate (Felger 2000). Thus, its cover area has been greatly diminished. The populations of the Large-billed Savannah Sparrow have been reduced as well, as witnessed in coastal California, where it winters (Unitt 1984) and in the breeding grounds

(Mellink and Ferreira-Bartrina 2000). However, its current abundance and trends are not known. Although the whole area covered by the saltgrass is protected by the Biosphere

Reserve, its major problem originates upstream.

Management Recommendations for the Saltgrass Avian Community

• Continue the protection as part of the core zone of the Biosphere Reserve

• Allocate freshwater, at least every 4 or 5 years, that could reach that area and propagate the saltgrass. The recommended pulse floods to maintain the riparian system could help this purpose.

Information needs for the Saltgrass Avian Community

• Trends in coverage of Palmer’s saltgrass and its relation with freshwater flows.

• Abundance and population trend of the Large-billed Savannah Sparrow.

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• The effect of fluctuations of freshwater flows on the Large-billed Savannah Sparrow.

Marine Zone Avian Community

This conservation target included the species of birds that depend upon the open marine areas of the Upper Gulf of California, in particular as feeding, post-breeding dispersal, and wintering sites. The goal of this target is to maintain the productive food web in these marine areas that sustains a diversity of birds and other wildlife.

The focal species for this group includes three species: Eared Grebe (Podiceps nigricollis), Black Storm-Petrel (Oceanodroma melania), and Brown Pelican (Pelecanus occidentalis). All of these species are common non-breeding visitors to this region

(Patten et al. 2001, Hinojosa-Huerta et al. in press[b]), and their population fluctuations could be used as an indicator of the health of these marine areas. Some of the nesting waterbirds use the marine zone for feeding, and would be benefited with conservation efforts as well.

Although marine zones are included either as part of the core or buffer zones of the

Biosphere Reserve, there are several threats to birdlife in these areas, but the information on their scale and impacts is limited. In particular, commercial fisheries could be causing an impact on the populations of marine birds, as well the reduction of freshwater flows.

Management Recommendations for the Marine Zone Avian Community

It is difficult to recommend management guidelines for the benefit of birds in this zone, due the limited knowledge of the threats and their effects on birds. An increase in

250 freshwater flows in the area could enhance the food web, but this is still the topic of scientific debate, and the amount of water that would be required to have an effect on this area is unknown.

Information needs for the Marine Zone Avian Community

• Determine population trends of focal species.

• Determine the effect of reduced freshwater flows on the populations of marine birds and their food sources.

• Determine the effect of fisheries on the populations of marine birds and their food sources.

Migratory Waterbirds

This group included the species of waterbirds that spend the winter or stop during their migration in the Colorado River delta. The emphasis is on those species of waterfowl and shorebirds that occur in the delta by the hundreds of thousands of individuals every year.

The goal of this target is ensure that the delta wetlands will continue to provide habitat for these species.

The focal species for this target include 10 birds from 3 families: Anatidae, Charadriidae, and Scolopacidae (Table 3). The focal species were selected to cover the major aquatic habitat types in the delta, as well as to include the most representative species of the group.

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At the continental level, populations of migratory waterbirds have declined due to wetland loss, and their habitats are threatened and still declining (Kushlan et al. 2002).

Wetland loss in the delta has impacted drastically the abundance of wintering waterfowl in the region. Hundreds of thousands of ducks and geese from at least 26 species used to visit the region in winter (Kramer and Migoya 1989), but habitat for wintering waterfowl has been reduced to a minimum of a few thousand hectares during the dry years (Glenn et al. 1996). Recent counts from aerial winter surveys estimate about 50,000 individuals during wet years (1993-1994) and just over 4,000 individuals during dry years (1995-

1996) (U.S. Fish and Wildlife Service 1993 to 1996). Wetlands at critical sites has been restored and maintained, especially at the Ciénega de Santa Clara and Hardy River, providing over 8,000 ha of habitat for waterfowl, which now support tens of thousands of wintering individuals every winter (Hinojosa-Huerta et al. in press[b]).

Given the cumulative impacts on these species, the Colorado River delta represents a major opportunity for the conservation and recuperation of these species. This is particularly important for shorebirds, especially at the mouth of the Colorado River and the Ciénega de Santa Clara. Over 150,000 shorebirds from 32 species visit the delta every year (Mellink et al. 1997, Morrison et al. 1992). For this reason, the delta is part of the

Western Hemisphere Shorebird Reserves Network (1993) and also a Wetland of

International Importance in the Ramsar Convention (1998). The western populations of

American White Pelicans (Pelecanus erythrorhynchos) also depend strongly on the

Colorado River delta during winter and migration (Patten et al. 2001). Overall, the

Colorado River delta is a critical piece of the Pacific Flyway, necessary for the

252 conservation of waterbird populations across Western North America (Anderson et al.

2003).

Management Recommendations for Migratory Waterbirds

Many of the recommendations are covered in other groups, as they basically require what has been the most limiting factor in the delta: water. The recommendations are:

• Secure water for the Ciénega de Santa Clara, at least at current flow and quality.

• Limit cattail expansion, preventing the closure of open water areas.

• Enhance wetlands in the Hardy River: 1) by managing agricultural runoff with dikes, to flood a larger area in the floodplain, and 2) by increasing the water flow through the

Hardy River.

• Enhance wetland areas in the Colorado River, by maintaining a constant instream flow and restoring water access to backwaters and secondary streams.

• Optimize the potential for wetland maintenance of agricultural drainage water, especially at Laguna del Indio and the eastern drains of the Mexicali Valley, by avoiding extended periods of desiccation and avoiding extreme fluctuations in water flows and salinity.

• Limit the expansion of extensive shrimp farms in the intertidal zone of the delta.

• Regulate and control hunting of waterfowl, to prevent any impacts on the population of these species.

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Information needs for Migratory Waterbirds

• Determine population trends.

• Evaluate the effect of restoration efforts on the abundance of wintering waterbirds.

• Evaluate the effect of freshwater on the wintering shorebirds of the delta, especially at the intertidal areas.

• Determine stay length and survivorship of wintering and migrant waterbirds in the delta.

• Determine the sustainable number of individuals (waterfowl) that can be hunted every winter in the delta.

STRATEGIES FOR IMPLEMENTATION

The general guidelines for the development and implementation of the Conservation Plan

are based on the principles of Partners in Flight (Rich et al. 2003), which include

protecting all bird species, helping the species at risk, maintaining common birds

common, and basing all actions on collaborative, voluntary efforts for the benefit of

birds, their habitats, and people, regardless of political boundaries

With the premises of those guidelines, and with the purpose of achieving the goals for the

conservation targets, we identified eight lines for action in the Colorado River delta:

1 – Collaborate with the Biosphere Reserve

The declaration of the Upper Gulf of California and Colorado River Delta Biosphere

Reserve in 1993 by the Mexican Government has been one of the major landmarks for

254 the conservation of the delta ecosystem and a clear statement of the commitment of

México for the protection of biodiversity in this region.

The main challenges that the Reserve has faced in the ten years of operation have been lack of adequate funding and understaffing, which have limited monitoring and enforcement activities. Nevertheless, the Reserve has been effective in protecting wetland areas, in particular the Ciénega de Santa Clara, and associated species, such as the Yuma

Clapper Rail. Major opportunities to collaborate with the efforts of the Reserve for bird conservation include the implementation of a joint monitoring plan (see Appendix C), which could help evaluate and guide the activities of the reserve, under the framework of adaptive management.

Another area for cooperative efforts is the implementation of a comprehensive outreach and environmental education program for the communities within the reserve, with the objectives of 1) developing alternative economic activities, such as nature tourism, under a framework of sustainable development and conservation of natural resources; 2) reducing the pressures in these areas, such as cattle grazing and over fishing; and 3) increasing the understanding within local communities of the linkages between the ecosystem health and the health of their communities, as well as the importance of the

Colorado River delta at a regional and continental scale.

2 – Protect the Floodplain

The Biosphere Reserve is mostly marine, and it protects only a portion of the Colorado

River floodplain. As such, the Hardy River and the riparian forests of the Colorado River

255 were left out the reserve and without protection. Land tenure in this area is federal, and is managed by the National Water Commission (CNA), but there is no mandate to protect or implement conservation actions. Furthermore, the area is being managed only under considerations for drainage of the Mexicali Valley and the prevention of floods, with dredging and vegetation clearings occurring periodically.

A major step to change this situation is to establish protection for the riparian corridors of the Hardy and Colorado rivers within the National System of Natural Protected Areas, with the implementation of a conservation mandate over the federal agencies for these rivers.

3 – Develop a Plan with CNA

The legal protection of the area is only one of the steps for the conservation of the

Colorado River in México. A major activity required in this long-term process is the development and implementation of a management plan for the floodplain, in coordination with the National Water Commission, the agency in charge of this area.

The plan should be formulated in a participatory manner with the input of local communities, and in the framework of adaptive management, in constant coordination with the monitoring efforts. The plan should address the environmental needs of the area, without jeopardizing the mandates for flood control that the CNA needs to meet. It should also specify the water needs for the environment and set guidelines to protect the riparian vegetation, as well as the secondary streams and backwaters. Finally, the plan must also identify and protect or restore the required processes that maintain the health of

256 the riparian system, in particular the processes that maintain the geomorphologic dynamism of the floodplain, securing its ecologic functionality in the long term.

4 – Secure freshwater flows

Together with the legal protection and the management plan, securing an environmental instream flow is one of the priority actions to accomplish the goals of the Bird

Conservation Plan for the Colorado River delta.

A secure allocation of water for the river has been identified as the critical factor limiting the restoration of the delta (Zamora-Arroyo et al. 2001). The required maintenance water is a continuous flow of about 2 m3/s (4 X 107 m3/year; Glenn et al. 2001). At this time,

additional water transfers between the United-States and México are not allowed under

the existing International Treaty (Cornelius et al. 2004), and water for environmental

purposes needs to be identified in México. Cooperative efforts between foundations,

environmental ngo’s and government agencies should be developed for the purchase of

the required water and implementing the delivery to the required areas.

It is important to acknowledge that this maintenance flow requires to be complemented

with a larger pulse flood every 4-5 years at 80-120 m3/s (3 X 108 m3/year), to foster

recruitment of native plants, wash salts, and rework sediments in the floodplain (Glenn et al. 2001, Zamora-Arroyo et al. 2001). However, to achieve this goal will require a greater involvement of the governments of México and United States, as well as the participation of the stakeholders of water rights in the Lower Colorado Basin.

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5 – Expand the Community-based Projects

The long-term success of restoration efforts is linked to the support of local communities

(Little 1994). In this sense, the Colorado River delta provide one of the greatest opportunities for restoration in the Sonoran Desert. As local communities are strongly connected to wetland resources, they are committed to the long-term conservation of these resources, and they have joined efforts to form a local organization to achieve these goals (Carrillo-Guerrero 2002).

One of the major milestones towards these goals has been the incorporation of local communities in the process, in particular through the representation of the Ecological

Association of Users of the Hardy and Colorado Rivers (AEURHYC). The organization was formed in 1998 by different sectors of the communities of the Hardy River to work together toward the restoration of the Colorado River delta. The association includes fishermen, farmers, the Cucapá tribe, aquaculturists, and the tourist sector. In particular, they call for 1) a modification of the 1944 Treaty between México and the United States to identify the delta ecosystem as an official “user” of Colorado River water, 2) the designation of all delta wetlands under a protection status, and 3) the implementation of community-based restoration projects (AEURHYC 2001).

Community support for wetland conservation also extends to farmers and landowners located close to the riparian areas. These farmers have shown their interest in maintaining native riparian vegetation, allotting water for the environment, protecting the Colorado

River floodplain with a conservation designation, and in participating in active restoration projects by leasing land and water (Carrillo-Guerrero 2002). These community activities

258 show that long-term restoration and conservation projects for wetlands can be implemented successfully in the Colorado River delta.

A major target for the future is to expand or develop similar groups to AEURHYC in other areas of the delta, which could improve the participation of local communities and multiply their reach in supporting the restoration of the Colorado River delta.

6 – Implement Restoration Projects

Three restoration projects are currently being implemented in the delta by a diverse group of local communities, environmental groups, government agencies, universities, and research institutions from the U.S. and México (Hinojosa-Huerta et al. in press). Each one of these projects has different specific objectives and is focused on a different type of ecosystem. A riparian/mesquite restoration project is being developed by a binational team of environmental and scientific institutions in the northern area of the Hardy River, in coordination with eight local tourist camps. South from there, the Ecological

Association of Users of the Hardy and Colorado Rivers has been working on the restoration of marsh wetlands in the Hardy River. Finally, restoration activities have continued at the Laguna del Indio, in the eastern part of the delta since 1998, in coordination with an ejido.

The common goal is to reestablish some of the ecological functions of the Colorado River delta, through a more efficient and environmentally sensitive use of the available water, which allows for the conservation of biodiversity and the preservation of social and cultural values of the region.

259

It is important to continue with these efforts, and expand them into the cottonwood- willow areas. It is also important to optimize the community interest that is already in place, as well as coordinate the on the ground restoration projects with the larger restoration effort in the delta and the allocation of instream water.

7 – Develop a Program for Environmental Education

Environmental Education (EE) is one of the best positive approaches for the conservation of birds and their habitats, as it is preventive and proactive. If properly articulated, environmental education can facilitate the implementation of conservation initiatives in the long term. The EE program for the Colorado River delta will be designed under the guidelines of: 1) providing the communities with the opportunities to acquire the knowledge, values, attitudes, commitment, and skills needed to protect and improve the environment, and 2) creating new patterns of behavior of individuals, groups, and society as a whole towards the environment.

The EE program in the delta should develop local awareness of the importance of the

Colorado River delta for the conservation of biodiversity, and reduce the local threats to this ecosystem, such as wildfires, wood cutting, illegal hunting, open trash areas, cattle grazing, and agricultural expansion.

A major part of the program should be based on a cooperative effort between NGO’s and the Secretaría de Educación Pública (Ministry of Education), to implement EE activities in public schools across the Colorado River delta. As such, the program will be defined as civil education for improved community and environmental ethics.

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8 – Develop an Outreach and Communications Program

This strategic line is devised as an enhancement of the community-based initiatives and the environmental education program, but more importantly, is targeted towards reaching a broader audience with the message of the restoration of the Colorado River delta.

The program should target the public in the cities of Mexicali and San Luis, that have not been involved as strongly as rural communities. In particular, it is important to reach out local governments and special interest groups that can support the conservation initiatives in the delta, including universities and education groups, different citizens’ councils such as the Colorado River Watershed Council (Consejo de Cuenca del Río Colorado), and

Citizens’ Council of the Colorado River (Consejo Ciudadano del Río Colorado), and private groups such as the Tourism Council and the Fisheries Council.

A critical aspect of developing such a program is to increase the awareness of the importance of the Colorado River delta and the issues happening in this region at a broader scale, in particular at a national level in México, and regionally across the border.

In this sense, the development of a media campaign will be one of the major targets.

ACKNOWLEDGEMENTS

We thank the following persons for their support, participation, and encouragement to

develop these strategies: Daniel W. Anderson, Carol Beardmore, Mark Briggs, Juan

Butrón, Jose Juan Butrón Alejandra Calvo, José Campoy, Raquel Castro, Steve

Cornelius, Roy Churchwell, Meredith de la Garza, Jaqueline García Hernández, Kimball

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Garrett, Edward Glenn, Onésimo Gonzalez, Sacha Heath, Miriam Lara Flores, Steve

Latta, William Mannan, Chris McCreedy, Eric Mellink, Robert Mesta, Kathy Molina,

Javier Mosqueda, Pamela Nagler, Eduardo Palacios, Eduardo Peters, Jennifer Pitt, Norma

Ramos, Juan Rivera, Martha Román, Sam Spiller, Pablo Valle, and Francisco Zamora.

The strategies were developed with the kind support provided by the National Fish and

Wildlife Foundation, Sonoran Joint Venture, U.S. Fish and Wildlife Service-Division of

Bird Habitat Conservation, and Wallace Foundation.

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Table 1. Bird species under a protection category in México of conservation concern in the Colorado River delta. Four codes are given for each species: Protection Category in México (SP – Special Protection, TH – Threatened, EN – Endangered, NP – No Protection), Breeding Status (NB – Non-breeding, BR – Breeding), Relative Abundance (EX – Extirpated, CA – Casual, RA – Rare, UN – Uncommon, CO – Common), and Temporal Presence (WI – Winter, SP – Spring, SU – Summer, PE – Perennial). Abundance categories follow Patten et al. (2001).

Species Protection Breeding Relative Temporal Category Status Abundance Presence Least Grebe SP NB CA SU Laysan Albatross TH NB RA SP Black Storm-Petrel TH NB CO PE Least Storm-Petrel TH NB CO PE Reddish Egret SP BR RA SU Roseate Spoonbill1 NP NB EX WI Fulvous Whistling-Duck1 NP BR EX SU Brant TH NB UN WI Bald Eagle2 EN NB UN WI Sharp-shinned Hawk SP NB UN WI Cooper's Hawk SP NB UN WI Harris' Hawk SP NB UN WI Red-shouldered Hawk SP NB CA WI Swainson's Hawk SP NB UN WI Ferruginous Hawk SP NB RA WI Peregrine Falcon SP NB UN WI Prairie Falcon SP NB RA WI California Black Rail EN BR RA PE Yuma Clapper Rail2,3 TH BR CO PE Virginia Rail SP BR CO PE Sandhill Crane1 NP NB EX WI Snowy Plover2 TH BR UN SU Heermann's Gull SP NB CO PE Gull-billed Tern1 NP BR CO PE Elegant Tern SP BR RA SU Least Tern2 SP BR UN SU Yellow-billed Cuckoo1 NP BR UN SU Western Screech-Owl1 NP BR RA SU Short-eared Owl SP NB RA WI Gilded Flicker1 NP BR EX SU Southwestern Willow Flycatcher1,2,4 NP BR EX SU Bell's Vireo1 NP BR RA SU Lucy's Warbler1,4 NP BR EX SU Summer Tanager1,4 NP BR EX SU Large-billed Savannah Sparrow3 SP BR CO SU 1 Species not under a protection category, but has experienced sharp population declines in the region. 2 Species also under federal protection in the U.S. 3 Species endemic to the Colorado River delta. 4 Breeding population has been extirpated, but still present as transient.

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Table 2. Ecozones of the Colorado River delta, México.

Ecozone Hectares Included Areas Habitat Types Main Threats Lack of instream Colorado River, from Morelos Cottonwood- Colorado flow and pulse 20,000 Dam to the confluence with the willow-saltcedar Floodplain floods, wildfires, Hardy River riparian forests and logging Hardy and Pescaderos Basin, Open water canals from Cerro Prieto to the Reduced flow and Hardy River 16,000 and saltcedar- confluence with the Colorado increased salinity cattail marshes River Ciénega de Santa Clara, El Cattail marshes, Unreliable water Off-channel Doctor, Cerro Prieto, Laguna 23,450 mudflats and sources and cattle Wetlands del Indio, and Andrade Mesa lagoons grazing Wetlands Intertidal Confluence of Hardy-Colorado Mudflats, saltgrass, Lack of freshwater and Marine 110,000 to El Golfo de Santa Clara and and open marine inflows and Zone San Felipe areas sediments Contaminants and Agricultural Agricultural fields, habitat loss due to 208,000 Mexicali Agricultural Valley Areas levees, and drains agricultural expansion

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Table 3. Conservation targets and focal species of the Colorado River delta.

México US Relative Breeding Habitat Status Continental

Status Status Abundance Status & Trend Assessments Marshbirds Least Bittern NP NP CO BR CO→ NWCP-NR Yuma Clapper Rail TH EN CO BR CO→ NWCP-NR Virginia Rail SP NP CO BR UN→ NWCP-NR California Black Rail EN CS RA BR EN ↓ NWCP-NR Nesting Waterbirds Snowy Egret NP NP CO BR UN ↓ NWCP-HC Snowy Plover TH EN RA BR TH ↓ SHCP - HI Gull-billed Tern NP CS UN BR UN→ NWCP-HC Black Skimmer NP NP UN BR UN→ NWCP-HC Riparian Birds Fulvous Whistling-Duck NP NP EX HB NE - NAWMP-NT Yellow-billed Cuckoo NP CS RA BR EN ↑ LCP-NC Southwestern Willow Flycatcher NP EN EX HB NE - LCP-TH&D Vermillion Flycatcher NP NP UN BR UN ↑ LCP-NC Bell's Vireo NP NP RA BR NE - LCP-TH&D Crissal Thrasher NP NP UN BR CO ↑ LCP-P&R Lucy's Warbler NP NP EX HB NE - LCP-RR Yellow-breasted Chat NP NP RA BR UN ↑ LCP-NC Song Sparrow NP NP CO BR CO ↑ LCP-NC Brown-headed Cowbird NP NP CO BR CO ↑ LCP-NC Bullock's Oriole NP NP UN BR UN ↑ LCP-NC Migratory Landbirds Rufous Hummingbird NP NP RA NB TH ↓ LCP-TH&D Pacific-slope Flycatcher NP NP CO NB UN ↓ LCP-P&R Warbling Vireo NP NP CO NB UN ↓ LCP-NC Swainson's Thrush NP NP CO NB UN ↓ LCP-NC Wilson's Warbler NP NP CO NB UN ↓ LCP-NC Western Tanager NP NP CO NB UN ↓ LCP-NC Saltgrass Avian Community Large-billed Savannah Sparrow SP NP UN BR TH ↓ LCP-NC Marine Zone Avian Community Eared Grebe NP NP CO NB CO→ NWCP-MC Black Storm-Petrel TH NP CO PB CO→ NWCP-HC Brown Pelican NP EN CO NB CO→ NWCP-MC Migratory Waterbirds Snow Goose NP NP CO NB UN ↓ NAWMP-IN American Wigeon NP NP CO NB UN ↓ NAWMP-IN Cinnamon Teal NP NP CO BR UN ↓ NAWMP-IN Northern Shoveler NP NP CO NB UN ↓ NAWMP-IN Black-bellied Plover NP NP UN NB UN→ SHCP - MC Whimbrel NP NP CO NB CO→ SHCP - HC Sanderling NP NP CO NB UN ? SHCP - HC Western Sandpiper NP NP CO NB CO ↓ SHCP - HC Short-billed Dowitcher NP NP CO NB CO ↓ SHCP - HC Wilson’s Snipe NP NP UN NB TH ↓ SHCP - MC

México Status: EN-Endangered, TH-Threatened, SP-Special Protection, NP-Not Protected. US Status: EN-Endangered, TH- Threatened, CS-Candidate Species. Relative Abundance: CO-Common, UN-Uncommon, RA-Rare, EX-Extirpated. Breeding Status: BR-Breeder, HB-Historic Breeder, NB-Non-Breeder. Habitat Status: CO-Common, UN-Uncommon, TH-Threatened, NE- Non-Existent. Habitat Trend: ↑-Increasing, ↓-Declining, → - Stable. Continental Assessments: NWCP-North American Waterbirds Conservation Plan, LCP-North American Landbirds Conservation Plan, NAWMP-North American Waterfowl Management Plan, SHCP-U.S. Shorebirds Conservation Plan, NR-Not Yet Rated, HC-High Concern, HI-Highly Imperiled, NT-No Trend Available, NC- No Concern, TH&D-Threatened and Declining, RR – Range Restricted, P&R-Requires Long-term Planning and Responsibility, MC- Medium Concern, IN-Trend Increasing.

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Table 4. Participants in the development of the Bird Conservation Plan for the Colorado River Delta. Name Institution Origin Daniel W. Anderson University of California at Davis Davis, CA Horacio de la Cueva CICESE Ensenada, Baja California Eric Mellink CICESE Ensenada, Baja California Steve Latta PRBO Conservation Science Stinson Beach, CA Kimball Garrett Los Angeles Natural History Museum Los Angeles, CA Kathy Molina Los Angeles Natural History Museum Los Angeles, CA Robert Mesta Sonoran Joint Venture Tucson, AZ Eduardo Palacios CICESE La Paz, Baja California Sur Jennifer Pitt Environmental Defense Boulder, CO Ray Stendell Salton Sea Science Office El Centro, CA Enrique Zamora Pronatura Sonora San Luis Río Colorado, Sonora Helena Iturribarría Pronatura Sonora San Luis Río Colorado, Sonora Chris McCreedy PRBO Conservation Science Stinson Beach, CA Jacqueline Garcia CIAD Guaymas, Sonora Alejandra Calvo IMADES San Luis Río Colorado, Sonora Martha Román IMADES San Luis Río Colorado, Sonora Yamilett Carrillo Pronatura Sonora San Luis Río Colorado, Sonora Jose Campoy RBAGDC, SEMARNAT San Luis Río Colorado, Sonora Miriam Lara AEURHYC Mexicali, Baja California Michael Vamstad AEURHYC Mexicali, Baja California Francisco Zamora Sonoran Institute Tucson, AZ Steve Cornelius Sonoran Institute Tucson, AZ Juan Butrón Ejido Johnson San Luis Río Colorado, Sonora Jose Juan Butrón Ejido Johnson San Luis Río Colorado, Sonora Onésimo Gonzales Comunidad Cucapá Mexicali, Baja California Javier Mosqueda Campo Mosqueda Mexicali, Baja California Edward Glenn University of Arizona Tucson, AZ Pamela Nagler University of Arizona Tucson, AZ William Shaw University of Arizona Tucson, AZ Osvel Hinojosa Pronatura Sonora San Luis Río Colorado, Sonora Charles van Riper U.S. Geological Survey Tucson, AZ Sam Spiller U.S. Fish and Wildlife Service Phoenix, AZ Mark Briggs Riparian Ecologist Tucson, AZ Eduardo Peters Instituto Nacional de Ecología México, D.F. Juan Carlos Barrera Pronatura Noroeste Hermosillo, Sonora Commission for Environmental Carlos Valdés Cooperation Montreal, Canada Jose Trejo Comisión Nacional del Agua Mexicali, Baja California Juan Rivera CIAD Guaymas, Sonora Gerardo Sánchez CIAD Guaymas, Sonora

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Figure 1. Ecozones and wetland areas of the Colorado River delta, México.