Studies in Avian Biology No. 37:28–45

DISTRIBUTION AND STATUS OF BREEDING LANDBIRDS IN NORTHERN

AARON D. FLESCH

Abstract. Northern Sonora, Mexico is dominated by steep elevation and rainfall gradients and a variety of vegetation communities with affi nity to the Sonoran, Madrean, Sinaloan, and Chihuahuan biogeographic provinces. Despite high environmental diversity and moderate accessibility, current information on distribution and abundance of breeding landbirds is limited throughout much of this vast region. Between 2000 and 2007, I surveyed landbirds in northern Sonora in four of the six primary watersheds that occur within 125 km of the US. I detected 161 of landbirds that I presumed were breeding (59% confi rmed) and four additional species that were possibly breeding during 568 site visits to 306 localities. I did not detect seven species that had been presumed to breed in the past, six of which likely still occur, or 10 species that I suspect may breed locally or irregularly in the study area. Based on probabilistic methods, I estimate that as many as 178 species of land- likely breed in the study area. Species richness within each of 16 secondary watershed regions increased as the number of major vegetation communities that were present increased, and presence of broadleaf riparian woodland, Madrean evergreen woodland, and Madrean montane conifer forest had the greatest infl uence on richness. Geographic ranges of many species that I observed were much larger than that suggested by previous studies likely as a result of increased effort. Evidence for some species however, suggested that distributions have either expanded or contracted, likely as a result of major changes in vegetation and perhaps climate change. Although some populations await discov- ery, my fi ndings suggest that northern Sonora supports higher richness of breeding landbirds than any other region of similar area in the borderlands of northern Mexico.

Key Words: borderlands, climate change, distribution, distributional change, landbirds, Mexico, Sonora, transboundary conservation, US-Mexico border.

DISTRIBUCIÓN Y ESTADO DE AVES TERRESTRES REPRODUCTIVAS EN EL NORTE DE SONORA, MÉXICO Resumen. El norte de Sonora, México esta dominado por un marcado gradiente altitudinal y de precipitación pluvial, así como por una variedad de comunidades vegetales con afi nidad a las provincias biogeográfi cas Sonorense, Madreano, Sinaloense y Chihuahuense. A pesar de la alta diversidad ambiental y cierta accesibilidad, la información actual de distribución y abundancia de aves terrestres reproductivas es limitada en gran parte de esta vasta región. Entre 2000 y 2007, realicé monitoreos de aves terrestres en el norte de Sonora, en cuatro de las seis principales cuencas que se ubican a 125 km o menos, de los Estados Unidos. Detecté 161 especies de aves terrestres que asumí estaban reproduciéndose (59% confi rmadas), y cuatro especies adicionales que posiblemente estaban reproduciéndose durante 568 visitas a 306 localidades. No detecté siete especies que se presumían en el pasado como reproductoras, seis de las cuales es probable que todavía ocurran, como tampoco 10 especies que sospecho se reproducen localmente o irregularmente dentro del área. Basado en métodos probabilísticos estimé que hasta 178 especies de aves terrestres probablemente se reproducen en el área de estudio. La riqueza de especies dentro de cada una de las 16 subcuencas incremento en la medida en que aumentaba el número de comunidades vegetales, y la presencia de bosques ribereños de hojas anchas, bosques siempre verdes Madreanos y bosques montanos de coníferas Madreanos tuvieron la mayor infl uencia en la riqueza. Los rangos geográfi cos de muchas especies que observé fueron mucho más grandes que lo sugerido por estudios previos, muy probablemente como resultado de un esfuerzo mayor. Sin embargo la evidencia para algunas especies, sugiere que ha habido expansión o contracción de sus distribuciones, probablemente como resultado de cambios mayores en la vegetación y quizás por cambios climáticos. Aunque algunas poblaciones esperan ser descubiertas, mis hallazgos sugieren que el norte de Sonora soporta mayor riqueza de aves terrestres reproductivas que cualquier otra región de área similar, en las tierras fronterizas del norte de México.

Information on the status, distribution, conserved before they are signifi cantly altered and habitat needs of wildlife are essential for or lost. Efforts to identify and manage wildlife effi cient conservation and management. In populations may be especially challenging near regions where little information is available and international boundaries because ownership, rapid environmental changes are anticipated, management objectives, and national priori- detailed information may be required to ensure ties often vary and development pressure and that populations are identifi ed, managed, and security concerns are often high. Despite these 28 BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 29 challenges, cooperation among neighboring (1957) provided detailed information in pine- nations can help achieve conservation objectives oak woodlands in many of the higher moun- in trans-boundary landscapes (Mittermeier et al. tains in northeast Sonora. Russell and Monson 2005, Plumptre et al. 2007). (1998) synthesized information from previous At approximately 600 km in length, the studies and collections from throughout Sonora international boundary between the state of that they supplemented with fi eld work in some Arizona in the US and the state of Sonora in regions of northern Sonora. Since these efforts, Mexico bisects a region of exceptional diversity. Hinojosa-Huerta et al. (2007) summarized sta- Spanning nearly a 10-fold range of annual rain- tus and provided additional records of birds fall, this region extends from mountains at the in the lower Colorado River Valley and adja- northern edge of the Sierra Madre Occidental cent areas of extreme western Sonora, Flesch west to the delta of the Río Colorado and sup- and Hahn (2005) described communities ports both highland vegetation communities in several little-known mountain ranges west of oaks (Quercus sp.) and pines (Pinus sp.) and of the region visited by Marshall (1957), and vast lowlands of Sonoran and Chihuahuan des- Villaseñor (2006) reported on wintering birds at ertscrub and grassland (Brown 1982). Complex several widely scattered localities. Despite these elevation and moisture gradients and conver- efforts, the large size of northern Sonora, limited gence of several major biogeographic provinces accessibility, and high environmental diversity foster high regional diversity and result in the have precluded a detailed assessment of distri- distributional limits of both Neotropical and bution and status of breeding landbirds. Nearctic species of plants and (Halffter To provide current information on land- 1987, Howell and Webb 1995, Turner et al. 1995, birds in the borderlands of northern Sonora, I Escalante et al. 2004). surveyed much of the region between 2000 and Large areas of the Sonora-Arizona border- 2007. Herein I summarize information on distri- lands are managed with explicit conservation bution and status of breeding landbirds, assess directives by the Mexican and US federal recent distributional changes, and describe pat- governments (Cartron et al. 2005, Felger et al. of species richness across the region. 2007), yet a number of environmental concerns exist (Liverman et al. 1999, Goodwin 2000). METHODS Although human population densities are low in many areas of northern Sonora, groundwa- STUDY AREA ter use and urban growth are increasing, sig- nifi cant areas of riparian vegetation have been I defi ned northern Sonora as the area within degraded or lost, and security concerns have 125 km of the international boundary with the culminated in ongoing development along US. Several major watersheds traverse this much of the international border (Cartron et al. region and many originate near the international 2005, Búrquez and Martínez-Yrízar 2007, Cohn boundary and fl ow in a north-south direction 2007). These and other factors may threaten (Fig. 1). In northeastern Sonora, the Río Yaqui long-term conservation objectives unless their begins in extreme southeast Arizona and south- effects are understood and information on west New Mexico and fl ows south through the distribution and status of plant and wild- Sonora toward the Gulf of California. To the life populations are known and monitored. west in the Gila watershed, the Ríos San Pedro Information on bird communities may be and Santa Cruz originate in mountains near especially valuable because relative to other the border, traverse small portions of Sonora, vertebrates birds are often good indicators of then fl ow north into Arizona. To the south, specifi c environmental conditions upon which the adjacent Río Sonora, and its tributaries the they depend (Canterbury et al. 2000, Bryce et al Ríos Bacanuchi and San Miguel, fl ow south 2002) and because birds are relatively easy to from mountains within 70 km of the border. detect and survey (Ralph and Scott 1981, Bibby Farther west in the Concepción watershed, the et al. 2000) Río Altar and Arroyo Sasabe, drain small areas Ornithological investigations in Sonora of south-central Arizona and the Río Magdalena began well over a century ago and continue and Arroyo Plomo originate immediately south to this day (Stephens 1885, Moore 1938, van of the border. These and several other tributar- Rossem 1945, Marshall 1957, Short 1974, Russell ies of the Río Concepción fl ow south before and Monson 1998, Rojas-Soto et al. 2002, converging and fl owing west toward the Gulf Villaseñor 2006). Despite these efforts, vast por- of California. In the more arid west, the Río tions of northern Sonora remained little studied Sonoyta and its tributary the Arroyo Vamori by the early 1950s (Phillips and Amadon 1952) drain a region immediately along the border after which additional work occurred. Marshall and empty into the sands of the Gran Desierto 30 STUDIES IN AVIAN BIOLOGY NO. 37

FIGURE 1. Map of study area in northern Sonora Mexico indicating boundaries of primary watersheds (dashed line) and major drainages and mountain ranges. The maximum elevation of each mountain range is in meters. Elevations are based on data from Instituto Nacional de Estadística, Geografía e Informática and my own mea- surements using a GPS. The small portion of the Yaqui watershed to the east was not considered nor were areas >125 km from the international boundary with the US. de Altar. Still west is the Río Colorado that dominated the Plains of Sonora subdivision drains much of the southwestern US. and occurred only in the extreme south-central In this study, I considered the Sonora, Gila, Concepción watershed (Shreve 1951), whereas Concepción, and Sonoyta watersheds that to the east, Chihuahuan desertscrub occurred together cover approximately 70% of northern only in the lower San Pedro watershed. In the Sonora and excluded the extreme western por- extreme south, Sinaloan thornscrub occurred tion of the Sonoyta watershed which is predom- locally on slopes in the Coyotillo-Magdalena- inately sand dunes. I did not consider the Yaqui Carrizo watersheds and was widespread only watershed where fi eld work is not yet complete in the southern portion of the San Miguel and or the much smaller Río Colorado watershed especially in the Bacanuchi-Sonora watersheds. which has been described elsewhere (Hinojosa- Semi-desert grassland occurred at elevations Huerta et al. 2007). To describe distribution of above desertscrub in north-central Sonora west breeding landbirds, I subdivided these four pri- to the upper Plomo and Vamori watersheds mary watersheds into 16 secondary watershed and more open expanses of plains grassland regions (Table 1) by combining some nearby occurred in the San Pedro and in the upper drainages or subdividing long drainages into Santa Cruz and Sonora watersheds. Above upper and lower sections. grasslands, Madrean evergreen woodland was Vegetation communities in the region dominated by oaks at low elevation and by oaks included large expanses of Sonoran desertscrub, and pines at high elevation; isolated stands of semi-desert and plains grassland, and smaller oak woodland occurred in mountains as far west areas of Chihuahuan desertscrub, subtropical as the upper Sasabe (Sierra San Juan) and upper thornscrub, and montane forest and woodland. Plomo (Sierra el Humo) watersheds. Woodland In the west, desertscrub of the Lower Colorado transitioned to Madrean montane conifer forest River Valley subdivision of the Sonoran Desert at high elevations in the Sierras el Pinito, Azul, was dominant throughout much of the lower Cananea (Elenita and Mariquita), los Ajos, Concepción and Sonoyta watersheds and was and to the east in the Yaqui watershed. These replaced by desertscrub of the Arizona Upland forests were dominated by pine and rarely by subdivision at higher elevation. Savannah Douglas fi r (Pseudostuga menziesii) or white fi r BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 31

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US. ABLE T INCLUDE INDICATES WAS STUDY THE Lower Lower Vamori Upper Lower Sonoyta Lower 13 14 16 Upper 11 12 Plomo 6 47 15 52 Lower 3 11 Plomo Concepción Upper 51 Sasabe 53 31 28 40 49 2 19 286 197 408 113 6 59 35 20 45 38 26 57 12 9 83 Sasabe 0 83 54 44 87 32 17 46 21 13 149.2–162.8 Altar 66 48 85 31 68 44 25 67 10 150 18 24 18 5 73 70 Altar 90 81.2–94.8 Cruz 3 73 2 92 3.5 4 154 156 106 109 Busani 3 89 0 89 3.5 113 116 82 Coyotillo-Magdalena-Carrizo Pedro 3 6 88 51 14 65 Cocospera-Bambuto 12 14 16 10 8 3 7 3 8 17 Santa Upper 128 134 95 6 16 San 144 79 120 24 12 11 20 3 22 12 31 Gila 7 Bacanuchi-Sonora 101 91 10 regions 73 Sonora 0 73 San Miguel Upper All 105.7–119.8 395 306 568 176 15 18 27 6 134.2–148.8 3.7 159.7–172.3 113 28 43 48 20 18 120 161 4.0 106 14 142 3.2 6 167 166 148 134 14 20 26 31 98 5 103

Primary watershed Transect Primary Site Total Watershed region Watershed Transects visits Sites visits Observed Historical observed 32 STUDIES IN AVIAN BIOLOGY NO. 37

(Abies concolor) that were restricted to the high- between mid-February and late August of each est elevations and mainly on east- and north- year. I visited some transects only once and facing slopes in the Yaqui watershed. Broadleaf visited others up to 11 times depending on tim- riparian woodland and gallery forest occurred ing of initial surveys, accessibility, interest, and along valley bottoms and in canyons within the location of other efforts (Flesch and Hahn several other vegetation communities and were 2005; Flesch and Steidl 2006, 2007). I prioritized dominated by willows (Salix sp.), Fremont cot- transects for secondary surveys when initial tonwood (Populus fremontii), and velvet ash surveys occurred before the anticipated arrival (Fraxinus velutina) at low elevation and by of migratory species and in areas where I sus- Arizona sycamore (Platanus wrightii), Arizona pected occurrence of rare species. walnut (Juglans major), and bigtooth maple Each transect consisted of a linear search (Acer grandidentata) at high elevation. area approximately 1–6 km in length. To survey transects, I walked linear routes that typically SITE SELECTION followed drainages and temporarily walked in perpendicular directions to investigate bird I used three methods to select sites for sur- activity or areas of interest. I recorded all spe- veys: (1) random placement of survey transects, cies of birds that I detected during surveys, (2) non-random placement of survey transects, estimated numbers of individuals or pairs, and (3) incidental observations. Random sam- noted any evidence of breeding, and walked pling provided inference to large portions of at variable speeds depending on the amount the study area whereas non-random sampling of bird activity and complexity of the terrain. allowed the fl exibility needed to effi ciently I often noted only presence and breeding locate and survey important environments that behavior of common species so that I could had low landscape coverage and otherwise low focus on detecting and estimating abundance of probability of being sampled. less common species and traverse larger areas To randomize placement of transects, I during morning. I surveyed during mornings generated a random sample of coordinates at but noted observations at other times of day or elevations ≤1,200 m that I stratifi ed by major night. To rouse birds and augment visual and vegetation community and allocated in pro- aural detection probabilities, I often mimicked portion to the coverage of each community. or broadcast recorded territorial calls of pygmy- At each point, I established one transect along during surveys, which is similar to the the closest drainage that was >2 m wide and method used by Marshall (1957). Along most within 1 km of a road in each of four possible transects that I selected randomly, I broadcast topographic formations (valley bottoms, lower calls of Ferruginous Pygmy- at 350–600 m bajadas, upper bajadas, and mountain can- intervals while simultaneously surveying for yons) that occurred within 20 km of each point. that species (Flesch 2003). Along transects that Selection was constrained to low and moderate I selected non-randomly, I mimicked or broad- elevations because most transects were initially casted calls of pygmy-owls at less systematic established for surveys of Ferruginous Pygmy- intervals. At night I broadcasted conspecifi c Owls (Glaucidium brasilianum; Flesch 2003). vocalizations to elicit responses from nocturnal To expand coverage across a broader range species on an opportunistic basis. I focused of elevations, I selected another sample of incidental observations on species that were transects non-randomly. I placed transects uncommon, rare or of interest, and recorded along drainages and occasionally on slopes or the number of individuals detected and any trails in riparian areas, large canyons, montane evidence of breeding. woodland and forest, grassland, and focused in areas that were not adequately covered by ran- ANALYSES dom transects or where I suspected the occur- rence of rare species with specialized habitat To describe status within each region, I requirements. I selected locations for incidental estimated relative abundance by dividing the observations opportunistically by noting obser- number of transects where a species was pres- vations while scouting, traveling between tran- ent by the total number of transects visited dur- sects, in camp, and at times of day that were not ing the breeding season. I used these estimates effi cient for transect surveys. and incidental observations to classify relative abundance as common (frequently encountered FIELD SURVEYS as individuals, pairs, or small groups), fairly common (a few individuals or pairs detected), I surveyed from February 2000 to June uncommon (present but may not be found in 2007 and focused during the breeding season a day or two of fi eld observations), and rare BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 33

(present but rarely detected and often restricted estimating latitudinal and longitudinal centers to localized area), as defi ned by Russell and and an index of environmental diversity equaled Monson (1998: 15). Species that were locally to the number of major vegetation communi- common but restricted to environments with ties present within each region and considered low coverage were often considered uncom- broadleaf riparian woodland as a community. mon. I presumed breeding was occurring if To determine vegetation communities that had individuals were singing, paired, territorial, the greatest infl uence on species richness, I used or exhibiting other circumstantial evidence of multiple linear regression with stepwise selec- breeding when birds were in typical breeding tion (P < 0.25 to enter, P < 0.10 to stay). To evalu- habitat during the breeding season. For raptors, ate adequacy of sampling, I assessed whether I presumed breeding was occurring if adults observed species richness and the number of were present in typical breeding habitat during species that were at least presumed to breed in the breeding season. I used more rigorous stan- the past but not detected during the study varied dards for species that were in atypical breeding with effort (site visits). habitat by presuming breeding was occurring only when a territorial pair, courtship, or other RESULTS behaviors indicative of breeding were observed. I did not presume breeding of migratory spe- EFFORT cies unless observations occurred outside peri- ods when populations typically migrate. To I completed 395 surveys along 176 transects, confi rm breeding, I used criteria of the North 70% of which I located randomly, and 173 American Ornithological Atlas Committee incidental surveys at 130 additional locali- (1990). To defi ne breeding habitat, distribu- ties (Table 1). Number of surveys per transect tion, and migration and wintering periods, I averaged 2.7 ± 0.1 (± SE) with 54% of transects supplemented my observations with data from visited ≥two times and 27% of transects vis- northern Sonora (van Rossem 1945, Marshall ited ≥four times. All effort combined yielded 1957, Russell and Monson 1998), adjacent por- 568 site visits to 306 sites, 92% of which were tions of southern Arizona (Monson and Phillips between 11 February and 31 August and 54% 1981, Rosenberg and Witzeman 1998 and 1999, were in May or June. I personally completed Rosenberg 2001, Corman and Wise-Gervais 77% of site visits, six observers each completed 2005), and other relevant literature (Poole 2005). 3–5%, and an additional four observers com- I then compared my fi ndings with information pleted the remaining 3% of visits all of which from these sources to assess potential changes were incidental observations. in status or distribution. Number of transects and total effort (site I calculated observed species richness visits) were approximately proportional to by summing all species that I presumed or the size of primary watersheds (Table 1, Fig. confi rmed to be breeding during the study 1). In the Concepción watershed, most effort within each region and calculated cumulative was in the Altar (28%), Coyotillo-Magdalena- observed species richness by including species Carrizo (21%), Sasabe (17%), and Plomo (17%) that I did not detect but that had been either watersheds and least effort was in the Busani presumed or confi rmed breeding in the past (8%), lower Concepción (6%), and Cocospera- (Marshall 1957, Russell and Monson 1998). Bambuto (4%). Effort was higher in Arizona Because all species are not detected perfectly upland desertscrub (45%) and semi-desert during surveys, I estimated species richness ( ) grasslands (36%) than in Madrean evergreen based on the abundance distribution I observed woodland (6%). Effort was low in Lower and a limiting form of the jackknife estimator Colorado River Valley (3%) and Chihuahuan (Burnham and Overton 1979) calculated by pro- (1%) desertscrub, plains grassland (3%), gram SPECRICH (J. E. Hines, available at http: Sinaloan thornscrub (3%), and in Madrean //www.mbr- pwrc.usgs.gov/software.html). montane conifer forest (1%), communities that To assess the range of likely values for each covered much smaller portions of the study estimate, I calculated 95% confi dence intervals. area. Effort in broadleaf riparian woodland I did not estimate species richness at the scale totaled 15% and most of these sites were in of watershed regions because sample sizes in semi-desert grassland (44%), Arizona Upland some regions were small. desertscrub (25%), plains grassland (9%), To assess the infl uence of large-scale geo- Sinaloan thornscrub (9%), and Madrean ever- graphic and environmental factors on cumulative green woodland (9%). observed species richness, I used linear regres- I visited virtually all major vegetation com- sion. As explanatory variables, I calculated the munities that occurred in lowlands within geographic position of each watershed region by each watershed region and only some that 34 STUDIES IN AVIAN BIOLOGY NO. 37 occurred in highlands. At high elevations, I surveyed portions of the Sierras los Ajos (Bacanuchi-Sonora), el Pinito and Cananea (Cocospera-Bambuto), Cucurpe (San Miguel and Coyotillo-Magdalena-Carrizo), las Avispas (Upper Altar), San Juan (Upper Sasabe), el Humo (Upper Plomo), el Cobre (Vamori), and el Durazno (Lower Sonoyta) (Fig. 1). Diffi cult access and time contraints prevented surveys at upper elevations in the San Pedro (Sierra San Jose), Santa Cruz (northeast Sierras el Pinito and San Antonio), Coyotillo-Magdalena-Carrizo (Sierra la Madera), Busani (south of Sierra las Avispas), Lower Sonoyta (Sierra Cubabi), and Lower Concepción (Sierra el Alamo) water- sheds and in areas above 1,300 m in the Sierra Azul (Cocospera-Bambuto and San Miguel), 1,200 m in the Sierra San Antonio (San Miguel and Bacanuchi-Sonora), and 1,600 m in the FIGURE 2. Association between species richness and Sierra el Chivato (Santa Cruz). the number of major vegetation communities pres- ent within each of 16 watershed regions in northern Sonora, Mexico. Richness equaled the number of SPECIES RICHNESS landbird species that were presumed or confirmed breeding during the study plus species that I did I observed 66 species of landbirds that I pre- not detect but that had been presumed or confirmed sumed were breeding and another 95 species breeding in the past. Richness increased by 15 ± 2 spe- that I confi rmed breeding. Four species (Wild cies with each additional vegetation community (t14 = [Meleagris gallopavo], Osprey [Pandion 6.58, P < 0.001). haliaetus], Fan-tailed Warbler [Euthlypis lachry- mosa], Western Meadowlark, [Sturnella neglecta]) increased from west to east (estimate ± SE = 3 ± possibly bred but evidence was not suffi cient to 1 species/10 km, t14 = 4.04, P = 0.001), once the presume so. I did not detect seven species that effect of vegetation was considered, richness had been at least presumed to breed in the past; did not vary with longitude (t13 = 1.21, P = fi ve were associated with high-elevation forests 0.25). Presence of broadleaf riparian woodland, (Flammulated Owl [Otus fl ammeolus], Blue- Madrean evergreen woodland, and Madrean throated [Lampornis clemenciae], montane conifer forest (t12 ≤ 2.29, P ≤ 0.04) Magnifi cent Hummingbird [Eugenes fulgens], infl uenced species richness more than presence

Pygmy Nuthatch [Sitta pygmaea], and Red- of other vegetation communities (t11 ≤ 1.61, P ≥ faced Warbler [Cardellina rubrifrons]), one with 0.14); when any of these communities were low desert (Le Conte’s Thrasher [Toxostoma present, richness averaged at least 40 ± 9 species lecontei]), and one with grassland (Northern greater than in regions where these communi- Bobwhite [Colinus virginianus]) (Tables 1 and 2). ties were absent. I estimate that 171 ± 3.7 species of landbirds at Observed species richness did not vary with least possibly breed (upper bound of 95% CI = effort (t14 = 0.50, P = 0.63), yet the number of 178) and that 166 ± 3.2 species at least presum- species that were at least presumed to breed ably breed (upper bound of 95% CI = 172) in the in the past but not observed during the study study area. decreased as effort increased (t14 = 2.20, P = 0.04). Within primary watersheds, species rich- On average, observed richness was 7 ± 2% lower ness was high in the Concepción and Sonora, than cumulative observed richness and differ- and low in the Sonoyta watersheds. Estimates ences were greatest in the lower Concepción of species richness within each primary water- (21%), Santa Cruz (17%), and Bacanuchi-Sonora shed were similar to observed values (Table 1); (17%) watersheds (Tables 1 and 2). observed richness averaged 5.6 ± 0.6% lower than that estimated and cumulative observed DISTRIBUTION AND STATUS richness differed from that estimated by only 2.9 ± 1.4%. I detected six species of breeding landbirds Cumulative observed richness increased by that had not been observed previously in the an average of 15 ± 2 species with each additional study area and many others that had been vegetation community present in a region (t14 = observed at few localities. Of species that had not 6.58, P < 0.001; Fig. 2). Although richness also been observed previously, Short-tailed Hawk BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 35

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Colinus virginianus Accipiter gentilis Patagioenas fasciata Buteo brachyurus Buteo albonotatus Cyrtonyx montezumae Buteo swainsoni Falco sparverius ARE Caracara cheriway Elanus leucurus Buteo jamaicensis Falco peregrinus

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WAS

2. D Common Black-Hawk ( ABLE Elegant ( Montezuma Quail ( ( Ciconiiformes Black Vulture ( Sonoyta Concepción Gila Sonora T OBSERVATIONS COMMON STATUS PRESUME Concepción Gila Sonoyta ( Turkey Wild Turkey Vulture ( Lower Plomo Vamori Plomo Sasabe Sasabe Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora Golden Eagle ( Red-tailed Hawk ( Crested Caracara ( American Kestrel ( Gambel’s Quail ( Quail Gambel’s Zone-tailed Hawk ( Prairie Falcon ( Northern Bobwhite ( ( Osprey White-tailed Kite ( Swainson’s Hawk ( Peregrine Falcon ( Short-tailed Hawk ( Cooper’s Hawk ( Sharp-shinned Hawk ( Columbiformes Rock Pigeon ( Band-tailed Pigeon ( Eurasian Collared-Dove ( Gray Hawk ( Harris’s Hawk ( Northern Goshawk ( White-winged Dove ( Mourning Dove ( 36 STUDIES IN AVIAN BIOLOGY NO. 37 ) R R R R U R U R R R R ) ) R R F R* U U U R R R* F ) ) R U U U U C R C C C ) C C ) R R U U U U U U U R R ) ) R R* U U U ) R U U U U U ) U U U U F U F U F U F U U F F U U ) ) R* ) ) U F U F F F U ) F F F F F F ) U R R F U F U ) F U U U ) R R R R R R R R R R R R R R R ) ) R R R R R ) ) U C U U C F C F C ) C U F F ) U C U* C U ) ) R R U R R ) ) R R R* R R ) R* R ) U C C U U C U R U* U* ) C C C C C R* ) ? R R ? R ? R* R ) R R ? ) R* ) ) R R ) violiceps Archilochus Lampornis ) R* R* R R Cynanthus Selasphorus ) U C U C C U U C U U Eugenes fulgens Glaucidium ) U R C U R C U C U U U U Megascops trichopsis ammeolus Columbina passerina fl Calypte costae Calypte anna Glaucidium gnoma Caprimulgus ridgwayi Coccyzus americanus Chordeiles minor Aeronautes saxatalis Megascops kennicottii . Geococcyx californianus Leptotila verreauxi Bubo virginianus Phalaenoptilus nuttallii Chordeiles acutipennis Otus ) R R R R R R* R R Athene cunicularia Caprimulgus vociferus Strix occidentalis ) R U R U U U R* ) ) R ) ) R* Columbina inca ) R U U F F C C C C Tyto alba ) R U R R R U* ONTINUED Micrathene whitneyi cent Hummingbird ( fi 2. C ABLE Greater Roadrunner ( ( Owl Elf Spotted Owl ( Common Nighthawk ( Lesser Nighthawk ( Nighthawk Lesser Strigiformes Barn Owl ( Flammulated Owl ( Whiskered Screech-Owl ( Great Horned Owl ( Northern Pygmy-Owl ( Burrowing Owl ( Common Poorwill ( Common Ground-Dove ( Cuculiformes Yellow-billed ( Western Screech-Owl ( Ferruginous Pygmy-Owl ( brasilianum Sonoyta Concepción Gila Sonora T Concepción Gila Sonoyta Inca Dove ( White-tipped Dove ( Lower Plomo Vamori Plomo Sasabe Sasabe Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora Buff-collared ( Whip-poor-will ( Whip-poor-will Broad-billed Hummingbird ( latirostris Violet-crowned Hummingbird ( White-throated Swift ( Broad-tailed Hummingbird ( platycercus Costa’s Hummingbird ( Anna’s Hummingbird ( Blue-throated Hummingbird ( Magni Black-chinned Hummingbird ( alexandri clemenciae BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 37 ) R R R U U U U U U U U U U U U U R R R ) ) C C C C ) ) C F F C F F C C U F C U U ) ) R R R ) ) R R R ) ) F F F F C F F C F F ) ) R R U U U R U U U U U R U R R ) ) R R R R R R R R R R R R R ) ) ? ? R U U U U U U U R ? U U ? ) ) R R U U F F F U F U F U U F F R R ) ) R U R* R ) U F U C F C C C F ) U U U R U R U U U R U ) ) C ) C C C ) R R R* R R ) ) R R R R R R R R R R R ) ) R R R R* R ) R R* R U R R R ) R R R U U R U R R R U U R ) ) R R* R U R U R U U F F F U ) R* R R R R U U U U U F U* F U U U U U R R R R ) R* ) R R R ) ) R ? R U U C R U R ) C R ? U U R ) C C U U U ) R R ) R ) R R* R R* ) R ) R R U U U U F F F F ) F U U U U R R ) U U R R R R Picoides scalaris ) R R* R R* ) R ) R R R* R R U U R Myiodynastes ) U R* U R R U U U U* U R U* R U ) U U U* U R R U R* U Myiarchus tuberculifer Myiarchus tyrannulus Empidonax fulvifrons Myiarchus cinerascens Empidonax occidentalis Contopus sordidulus ) R U R U U U U Tyrannus crassirostris ) R R U R U R* U U U Pachyramphus aglaiae Picoides arizonae Pyrocephalus rubinus Myiarchus nuttingi . Melanerpes formicivoru Picoides villosus Lanius ludovicianus Tyrannus melancholicus Tyrannus verticalis Tyrannus vociferans Melanerpes uropygialis Vireo plumbeus Chloroceryle americana Colaptes auratus elegans Vireo huttoni Contopus pertinax Colaptes chrysoides Sayornis nigricans Sayornis saya Cyanocitta stelleri ) R R R* R Vireo bellii sher ( sher fi ONTINUED 2. C Camptostoma imberbe ABLE Western Wood-Pewee ( Buff-breasted Flycatcher ( Cordilleran Flycatcher ( Greater Pewee ( Black Phoebe ( Say’s Phoebe ( Passeriformes Beardless-Tyrannulet Northern ( Vermilion Flycatcher ( Dusky-capped Flycatcher ( Ash-throated Flycatcher ( Hairy Woodpecker ( Ladder-backed Woodpecker ( Arizona Woodpecker ( Northern Flicker ( Gilded Flicker ( Hutton’s Vireo ( Steller’s Jay ( Nutting’s Flycatcher ( Brown-crested Flycatcher ( Coraciformes King Green Sonoyta Concepción Gila Sonora T Concepción Gila Sonoyta Trogoniformes Elegant Trogon ( ( Woodpecker Acorn Woodpecker ( Gila Lower Plomo Vamori Plomo Sasabe Sasabe Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora Plumbeous Vireo ( Bell’s Vireo ( Loggerhead Shrike ( Rose-throated Becard ( Western Kingbird ( Sulphur-bellied Flycatcher ( Cassin’s Kingbird ( Thick-billed Kingbird ( luteiventris Tropical Kingbird ( 38 STUDIES IN AVIAN BIOLOGY NO. 37 ) C C F R C ) U ) U U U U* U U U ) ) C C C C C C C C C U C F F C F ) U U* ) C C R ) F U* ) R R R ? ) ) R U F F U F R F U ) ) U U F ) F U U R C F F U ) R* R R* R* R* R ) R* ) R ? R ? R ) ) F ? U U F ? F ? F ? ) U F ? ? U F ? F F ? ) R R R R U C C U U U C R R C U R R ) ) U* U* ) ) R* R* R R R* ) ) R* U* R R U R* ) R R* R ) ) R R R F F U U U U U R ) R F F R ) R R* R R* R ) ) R R ? U U F F C C C C C ) R R R R R* R* R R* R R* R R R* R ) R* R R ) R U U F U R* U R R U R* ) U R U R R* U R U F U F F ) R R* R R* R ) ) R R R* R R* R R ) ) U* R* R* R U* C R R* ) U* R* U* ) F F U C R R C C C C ) R* R* R* ) R* ) C U F U F U C C C U F F C C C F ) ? R R R R* U U U U R U ) R ) R ) R R R ) ) U U U U ) F F F F ) F C C U F R R R ) R R R R R ) R Polioptila nigriceps ) U F U U U* F F F U R R ) R R U R R U R R R* R Sitta carolinensis ) C C F F C C Polioptila melanura Mimus polyglottos Polioptila caerulea Toxostoma curvirostre Tachycineta thalassina Toxostoma lecontei . Corvus cryptoleucus Toxostoma bendirei Aphelocoma californica Sturnus vulgaris aviceps Baeolophus wollweberi Sitta pygmaea fl Sialia sialis Toxostoma crissale Turdus migratorius Corvus corax Vermivora luciae Certhia americana Thryomanes bewickii Peucedramus taeniatus Progne subis Catherpes mexicanus Hirundo rustica Petrochelidon pyrrhonota Thryothorus Thryothorus feliz Eremophila alpestris Campylorhynchus brunneicapillus Troglodytes aedon Phainopepla nitens Aphelocoma ultramarina Salpinctes obsoletus ONTINUED Psaltriparus minimus Auriparus 2. C Stelgidopteryx serripennis ABLE Rock ( White-breasted Nuthatch ( Pygmy Nuthatch ( Brown Creeper ( Cactus Wren ( Canyon Wren ( Cliff Swallow ( Sinaloa Wren ( Happy Wren ( Bushtit ( Bushtit Verdin ( Verdin House Wren ( ( Phainopepla Bewick’s Wren ( Blue-gray Gnatcatcher ( Curve-billed Thrasher ( European Starling ( Lucy’s Warbler ( Sonoyta Concepción Gila Sonora T Concepción Gila Sonoyta Western Scrub-Jay ( Northern Rough-winged Swallow ( Lower Plomo Vamori Plomo Sasabe Sasabe Barn Swallow ( Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani Bridled Titmouse ( San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora Black-tailed Gnatcatcher ( Black-capped Gnatcatcher ( Bendire’s Thrasher ( Le Conte’s Thrasher ( ( Warbler Olive Mexican Jay ( Purple Martin ( Violet-green Swallow ( American Robin ( Northern Mockingbird ( Common Raven ( Horned Lark ( Eastern ( Crissal Thrasher ( Chihuahuan Raven ( BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 39 ) R R R R* R ) ) R* R* ) ) C C C C F C F F C U ) C F U U ) R U U U U U U U U U R ) ) R* R* R* R* R R F ) U F U F F F ) R U R R U R U R U R U U ) U R U R ) R R R R* R* U R U R* R R* R R ) ) R F R R U U F F U U U U U U U F F U U U U R R F R ) ) U R R R R F R R R R F R R R U ) ) ? ? ) ceps frons ) R* ) ) ? ? ) fi fi ) U U U ) U F U F U U U F U U ) U F F U ) ) R* U U F ) R* U U ) R R* R* R ) U R R* U R U R U U C R* U F ) U R* R C U ) R R R* U R U R U U U U U U ) R F R* F R R F F F F ) U R R U U C U U U C ) R R U U U ) R R R R* R ) R R R ) ) R U R U U ) U F R* U* F R R F F F F F F ) R U U R R U F C U U U C ) R R F U U U R ) R R R R* ) R R U U U U F F U F ) F U U U U R R ) U R U R U R U R U R U R R* R R* U* Dendroica ) U R R R U U ) C C C C C ) U U U ) U Aimophila ru ava Aimophila carpalis fl Basileuterus ru Amphispiza bilineata Pheucticus Geothlypis trichas Agelaius phoeniceus Ammodramus Icteria virens Sturnella neglecta Sturnella magna Aimophila quinquestriata Quiscalus mexicanus . Passerculus sandwichensis Euthlypis lachrymosa Junco phaeonotus Cardellina rubrifrons Cardinalis cardinalis Aimophila botterii Aimophila cassinii Piranga rubra Myioborus pictus Piranga Pipilo fuscus Pipilo maculatus Dendroica graciae Pipilo aberti Dendroica petechia Passerina versicolor ) R R R R R R U R Passerina cyanea Passerina caerulea Melospiza melodia Chondestes grammacus ) ) C Cardinalis sinuatus ) ) R R ONTINUED 2. C ABLE Five-striped Sparrow ( Lark Sparrow ( Botteri’s Sparrow ( Yellow-eyed Junco ( Black-throated Sparrow ( Savannah Sparrow ( Grasshopper Sparrow ( savannarum Song Sparrow ( ( Black-headed Grosbeak ( ( Bunting Blue Grosbeak ( Indigo Pyrrhuloxia ( Pyrrhuloxia melanocephalus Abert’s Towhee ( Summer Tanager ( Spotted Towhee ( Canyon Towhee ( Rufous-crowned Sparrow ( Cassin’s Sparrow ( Rufous-winged Sparrow ( Yellow-breasted Chat ( Hepatic Tanager ( Great-tailed Grackle ( Western Meadowlark ( Varied Bunting ( Common Yellowthroat ( Fan-tailed Warbler ( Sonoyta Concepción Gila Sonora T Concepción Gila Sonoyta Yellow Warbler ( Black-throated Gray Warbler ( Grace’s Warbler ( Painted Redstart ( Rufous-capped Warbler ( Lower Plomo Vamori Plomo Sasabe Sasabe Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora nigrescens Red-winged Blackbird ( Eastern Meadowlark ( Red-faced Warbler ( 40 STUDIES IN AVIAN BIOLOGY NO. 37

(Buteo brachyurus), Eurasian Collared-Dove (Streptopelia decaocto), Violet-green Swallow (Tachycineta thalassina), and Happy Wren (Thryothorus felix) were presumed breeding in at least two watershed regions, and Fan-tailed Warbler and Western Meadowlark were pos- sibly breeding in one. Of species that had been observed previously at only a single locality, I presumed breeding by Cordilleran Flycatcher (Empidonax occidentalis) in one additional water- shed region, White-tailed Kite (Elanus leucurus), White-tipped Dove (Leptotila verreauxi), and Nutting’s Flycatcher (Myiarchus nuttingi) in two, Sinaloa Wren (Thryothorus sinaloa) and Rufous- capped Warbler (Basileuterus rufi frons) in three, Thick-billed Kingbird (Tyrannus crassirostris) in four, and Five-striped Sparrow (Aimophila quin- questriata) in fi ve additional watershed regions. Of species that had been observed previously at only two localities, I presumed breeding by Elegant Quail (Callipepla douglasii) in one, Streak-backed Oriole (Icterus pustulatus) in three, and Buff-collared Nightjar (Caprimulgus ridgwayi) in four additional regions (Table 2). All of these species were rare or uncommon. Breeding distribution of many species was much broader than that suggested by previous studies. For example, I detected several spe- cies that typically breed in riparian woodlands including Gray Hawk (Buteo nitida), Yellow Warbler (Dendroica petechia), and Summer Tanager (Piranga rubra) at numerous localities in the Altar, Santa Cruz, and San Pedro water- sheds where they had either not been docu- mented or had been presumed to breed at only single localities. Similarly, I detected several species that typically breed in oak woodlands including Whiskered Screech-Owl (Megascops trichopsis), Hutton’s Vireo (Vireo huttoni), and Hepatic Tanager (Piranga fl ava) in the upper Altar and upper Sasabe watersheds which is west of areas where they had been presumed to breed; Northern Flicker (Colaptes auratus), Arizona Woodpecker (Picoides arizonae), and Dusky-capped Flycatcher (Myiarchus tubercu- lifer) occurred still farther west in oak wood- lands in the upper Plomo watershed. I detected ) U ) F F F F U F F F F ) ? U R R R R* R U ? ) species that typically breed in grasslands ) U U R R F R R R R* U R U R R* R R F R R ) U U ) C C C C ) R U R R* U F U F F C U F U ) U U U U

) U R R U U U U F U U including Swainson’s Hawk (Buteo swainsoni) ) R R U R U U ? U F ? F U U ) U ? R U R R ) U U R U R U U U U F U U and Botteri’s Sparrow (Aimophila botterii) west

Molothrus ater to the Vamori watershed and Cassin’s Sparrow

Icterus pustulatus (Aimophila cassinii) west to the upper Plomo .

Molothrus aeneus watershed. American Kestrel (Falco sparverius), Carduelis psaltria Icterus bullockii Passer domesticus Icterus cucullatus Brown-crested Flycatcher (Myiarchus tyran- Icterus parisorum Carpodacus mexicanus nch ( nch

fi nulus), Bell’s Vireo (Vireo bellii), and Lucy’s ONTINUED Warbler (Vermivora luciae) were at least pre- sumed breeding in all 16 watershed regions 2. C despite lack of previous records in many of

ABLE these regions. House Sparrow ( Scott’s Oriole ( Gold House Finch ( Lesser Bullock’s Oriole ( Streak-backed Oriole ( Hooded Oriole ( Sonoyta Concepción Gila Sonora T Concepción Gila Sonoyta Bronzed Cowbird ( Brown-headed Cowbird ( Lower Plomo Vamori Plomo Sasabe Sasabe Altar Sonoyta Santa Cocospera- Altar Coyotillo San Busani San Bacanuchi- Lower Upper Bambuto Miguel Pedro Cruz Magdalena Sonora BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 41

Distribution and abundance varied widely other region of similar area in the borderlands among watersheds. Scaled Quail (Callipepla of northern Mexico. squamata), Botteri’s Sparrow, Grasshopper Using probabilistic methods, I estimated that Sparrow (Ammodramus savannarum), and Eastern as many as 178 species of landbirds likely breed Meadowlark (Sternella magna) were restricted in the study area. Information from Sonora mainly to the San Pedro and occasionally the (Russell and Monson 1998; A. D. Flesch, unpubl. Santa Cruz and Vamori watersheds; Scaled data) and neighboring southern Arizona Quail occurred locally west to the upper Plomo (Corman and Wise-Gervais 2005), combined watershed. White-tipped Dove and Nutting’s with vegetation associations that I observed, Flycatcher were restricted to the Bacanuchi- suggest 10 additional species may breed Sonora, San Miguel, and Coyotillo-Magdalena- locally or irregularly in the study area (Ruddy Carrizo watershed regions, whereas Sinaloa Ground Dove [Columbina talpacoti], Long-eared Wren and Black-capped Gnatcatcher (Polioptila Owl [Asio otus], White-eared Hummingbird nigriceps) occurred in these and the Cocospera- [Hylocharis leucotis], Berylline Hummingbird Bambuto watershed. I observed Happy Wren [Amazilia beryllina], Lucifer Hummingbird at only single localities in both the Bacanuchi- [Calothorax lucifer] Flame-colored Tanager Sonora and Coyotillo-Magdalena-Carrizo [Piranga bidentata], Chipping Sparrow [Spizella watersheds. Sharp-shinned Hawk (Accipiter passerina], Black-chinned Sparrow [Spizella striatus), Northern Goshawk (Accipiter gentilis), atrogularis], Red Crossbill [Loxia curvirostra] and and Broad-tailed Hummingbird (Selasphorus Pine Siskin [Carduelis pinus]). Rusty Sparrow platycercus) presumably bred only in the (Aimophila rufescens) was once detected just Sierra los Ajos (Bacanuchi-Sonora watershed); south of the study area (Thayer and Bangs 1906) Cordilleran Flycatcher, Buff-breasted Flycatcher and could also breed locally in the Bacanuchi- (Empidonax fulvifrons), and Plumbeous Vireo Sonora region. Although I obtained evidence (Vireo plumbeus) occurred in the Sierra los Ajos that Hermit Thrush (Catharus guttatus) and and to the west in one–two mountain ranges in Western Tanager (Piranga ludoviciana) breed the Cocospera-Bambuto watershed. in mixed-conifer forest just east of the Yaqui- Sonora divide (A. D. Flesch, unpubl. data), in DISCUSSION Sonora these species and possibly Warbling Vireo (Vireo gilvus) are likely restricted to the SPECIES RICHNESS upper Yaqui watershed. Breeding species that have been observed combined with those I Northern Sonora, Mexico supports a expect may occur suggest estimates of species wide range of environments and a rich and richness that I calculated are accurate. varied avifauna. Between 2000 and 2007, I Not surprisingly, species richness increased recorded 161 species of landbirds that I at markedly with the number of major vegetation least presumed were breeding in the Sonoyta, communities that were present in a region. As Concepción, Gila, and Sonora watersheds such, regions in the east that had broader eleva- within 125 km of the international boundary tion ranges and therefore greater environmental with the US. Including seven additional spe- diversity had higher richness. Presence of broad- cies that had been recorded previously, 168 leaf riparian woodland, Madrean evergreen species of landbirds have been at least pre- woodland, and Madrean montane conifer forest sumed to breed in the region, and all except had the greatest infl uence on species richness Northern (Masked) Bobwhite likely still occur. indicating that these vegetation communi- In comparison to estimates from neighboring ties supported more species with specialized Arizona between 1993 and 2000 (Corman and requirements than other communities in the Wise-Gervais 2005), northern Sonora supports region. In contrast, although richness was also approximately 35% fewer species of breeding high in regions with Sinaloan thornscrub, this landbirds in an area approximately one-tenth community likely had less of an overall effect on the size and with 45% less elevation range; richness because many species that are associated including additional species in the adjacent with thornscrub, such as Buff-collared Nightjar, northern Yaqui watershed lowers this esti- Black-capped Gnatcatcher, and Five-striped mate to at most 31% (Marshall 1957, Russell Sparrow, also occurred away from thornscrub in and Monson 1998; A. D. Flesch, unpubl. data). dense desertscrub and woodland. Although estimates are not available for other regions of northern Mexico, large-scale pat- DISTRIBUTION PATTERNS terns of bird distribution (Howell and Webb 1995) suggests that northern Sonora supports Bird species that occurred in desertscrub higher richness of breeding landbirds than any were universally more common and widespread 42 STUDIES IN AVIAN BIOLOGY NO. 37 than species that were typically associated with CHANGES IN DISTRIBUTION AND STATUS grassland, thornscrub, oak woodland, or conifer forest. Species that were found predominantly in Patterns of distribution represent a oak woodland, grassland, and broadleaf riparian complex response to a range of factors including woodland were typically rare and had much the arrangement and size of resource patches, narrower and more fragmented distributions. physiological tolerances, and biotic interactions Species associated with conifer forest were rar- that vary in space and time (Andrewartha and est and were largely restricted to high elevations Birch 1954, MacArthur 1972, Brown 1995). In in the Sierra los Ajos, Cananea, Pinito, and as northern Sonora, my observations indicate that described by Marshall (1957), in the Sierra Azul. a wide range of species are distributed across Grassland species were especially rare in the much larger areas than suggested by previous west with some species reaching the western studies. Determining whether these patterns edge of their distribution on the east sides of are due to actual changes in bird distribution the Sierras el Humo and el Cobre. Grassland or limited effort during past studies is diffi cult species were more abundant and widespread in because few data on localities where species the upper Santa Cruz and especially in the upper were undetected are available and because San Pedro watersheds where plains grassland there are few historical accounts of vegetation with high levels of horizontal and vertical veg- conditions and change in Sonora. etation cover still persist. Breeding populations Limited fi eldwork in many regions of north- of species that occurred only in broadleaf ripar- ern Sonora likely explains the wider patterns of ian woodland did not occur west of the Río Altar distribution that I observed of a broad range of and were largely restricted to the Riós Altar, species. Russell and Monson (1998) for exam- Bambuto, Magdalena, and portions of other ple, cited just four records of Brown-crested major valley bottoms to the east. Flycatcher west of the Río Bambuto, north of the Northern Sonora supports the westernmost Río Concepción, and east of the Río Sonoyta, yet and northernmost patches of some vegetation this species and its habitat are common or fairly communities and these patterns have impor- common in all 11 watershed regions in this vast tant implications for bird distribution. Isolated region. Distribution of other widespread migra- stands of oak woodland in the Sierra el Humo tory species such as Bell’s Vireo and Lucy’s for example, are the westernmost Madrean Warbler were also understated, yet this pattern evergreen woodland in the Madrean Sky was somewhat less evident for resident spe- Islands, mountains that form the northern and cies, suggesting that survey effort during the western extensions of Sierra Madre Occidental breeding season had been limited. Similarly, (Marshall 1957, Warshall 1995). As such, popu- many rare species that occurred in isolated or lations of birds that are associated with oak otherwise disjunct vegetation communities had woodland in the Sierra Madre Occidental, such also gone undetected. If Phillips and Amadon as Arizona Woodpecker, reach the western (1952) or Russell and Monson (1998) had visited edge of their global distribution in the Sierra el oak woodlands in the Sierra San Juan and Sierra Humo (Flesch and Hahn 2005). Similarly, oak el Humo during the breeding season rather than woodland in the nearby Sierra San Juan sup- in fall, they probably would have detected many ported several additional species of birds that I of the same species that I recorded. Previous did not detect to the west in the Sierra el Humo, fi eldwork seems to have been most limited in including Whiskered Screech-Owl, which reach the San Pedro, Altar, Busani, Sasabe, Vamori, the northwestern edge of their global distribu- and Plomo watersheds where many breeding tion here and in the neighboring Baboquivari species had not been previously documented. Mountains of Arizona (Phillips et al. 1964). Where known, patterns of vegetation change Species typically associated with Neotropical in northern Sonora have been complex and vari- environments such as Elegant Quail, White- able (Bahre and Hutchinson 2001, Turner et al. tipped Dove, Nutting’s Flycatcher, and Sinaloa 2003), and these changes have likely infl uenced Wren were restricted mainly to three or four bird distribution. In high-elevation pine forests watersheds in the more humid south-central in the Cocospera-Bambuto watershed for exam- and southeast portions of the study area. The ple, presence of Cordilleran Flycatcher, Buff- northernmost patches of Sinaloan thornscrub breasted Flycatcher, and Plumbeous Vireo in that had similar structure and composition mountain ranges where they were not observed to that found further south occurred in and by Marshall (1957) is likely attributable to recov- northeast of the Sierra Cucurpe and at low to ery of these forests following extensive logging moderate elevations in the Bacanuchi-Sonora that occurred just prior to Marshall’s visits. In region and these were the only regions where I contrast, although presence of species that are observed Happy Wren. associated with oak woodland in the Sierras San BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 43

Juan and el Humo could also be related to vege- to breed in this region in the past. Similarly, tation change, evidence suggests distribution of although I found small, localized populations of these woodlands has been largely stable in the some grassland birds south and west of Sasabe, region during recent times (Bahre and Minnich these species were likely much more abundant 2001) despite some recession at lower elevations and widespread before these grasslands were (Turner et al. 2003). largely degraded or lost (Brown 1900, 1904; In vegetation communities that are typically Bahre 1991, Turner et al. 2003), as suggested by more dynamic, such as broadleaf riparian wood- Stephens’ (1885) observation of the now extir- land (Webb et al. 2007), attributing changes in pated Northern Bobwhite. bird distribution to vegetation change is more More widespread distributions of some spe- diffi cult. In the San Pedro Valley for example, cies are likely the results of range expansion many riparian species such as Gray Hawk, that has occurred largely independent of major Yellow Warbler, and Summer Tanager may not changes in vegetation. Comparing my fi ndings have been widely documented because gallery with previous observation from Sonora (Russell forests were once rare or absent. In 1892 and and Monson 1998) and the southwestern US 1893, Mearns (1907) observed only scattered suggests recent range expansions of the fol- broadleaf trees along the Río San Pedro at the lowing species: White-tailed Kite (Monson international boundary, and gallery forests of and Phillips 1981, Gatz et al. 1985), Short- cottonwood and willow did not develop until tailed Hawk (Corman and Wise-Gervais 2005, the 1960s and especially in the late 1970s and Williams et al. 2007), Buff-collared Nightjar 1980s (Webb et al. 2007). (Bowers and Dunning 1997), Thick-billed In the Altar Valley, however, where most Kingbird (Phillips 1968, Monson and Phillips species of riparian birds had been described 1981), Sinaloa Wren (Russell and Monson only in the extreme upper watershed at Rancho 1998), Rufous-capped Warbler (Rosenberg la Arizona (van Rossem 1931), broadleaf ripar- and Witzeman 1999), Five-striped Sparrow ian woodland has likely been present for (Groschupf 1994), and Streak-backed Oriole some time. Nentvig et al. (1980) for example, (Corman and Monson 1995, Corman and Wise- described presence of permanent surface water Gervais 2005). Eurasian Collared-Dove rapidly along many portions of the Río Altar in 1764 expanded across much of North America since and Shreve (1951) noted that virgin mesquite arriving in Florida in the early 1980s (Romagosa woodlands persisted near Tubutama into the and McEneaney 1999) and recent arrival in 1950s despite elimination from virtually all Sonora since at least 2004 (Gómez de Silva 2004) other major valley bottoms in the Sonoran is not surprising. Although I found Zone-tailed Desert at that time. Therefore, despite only Hawk (Buteo albonotatus) to be much more com- recent description of breeding bird communi- mon and widespread in western Sonora than ties in the cottonwood-willow forests along the had been described previously, its presence in Río Altar, these communities have likely been western Arizona since at least 1939 (Phillips et present for some time. al. 1964) suggests distribution has been largely Although lack of previous effort and vegeta- static in this region despite recent expansion tion change may explain why I observed much to the north (Johnson 1994, Corman and Wise- broader patterns of distribution for some spe- Gervais 2005). In contrast, although I also found cies, distribution and abundance of many of Gray Hawk at many new localities, especially these same species may in fact be much more in the west and at somewhat higher elevations, limited than in the past. Along the Río Altar, this species has likely expanded its range due for example, completion of the Cuauhtémoc to vegetation change and other factors. Gray Dam and Reservoir (Presa Cuauhtémoc) in 1950 Hawk were not documented along the Río diverted surface water and likely contributed to San Pedro until 1963 (Phillips et al. 1964) and increased vegetation clearing for agriculture, have recently expanded into central Arizona degradation of gallery forests, and subsequent (Corman and Wise-Gervais 2005). declines in distribution and abundance of birds Most species that I found to be more associated with these forests. Early descriptions widely distributed or present for the fi rst of birds and vegetation along the lower Río time in northern Sonora have likely expanded Concepción are available (Stephens 1885, Neff their geographic ranges from more tropical 1947, Phillips and Amadon 1952). Undoubtedly, regions to the south (e.g., Short-tailed Hawk, complete elimination of the once extensive White-tipped Dove, Buff-collared Nightjar, mesquite woodland near Pitiquito and Caborca Thick-billed Kingbird, Sinaloa Wren, Happy caused the local extirpation of many species of Wren, and Rufous-capped Warbler). Although birds and in part, explains why I failed to detect wider occurrence of some of these species 21% of species that had been at least presumed could be attributable to increased effort, this 44 STUDIES IN AVIAN BIOLOGY NO. 37 seems unlikely, because many of these same 1998 and 1999, Rosenberg 2001, Corman and species have recently occurred for the fi rst Wise-Gervais 2005) information is available. time or become regular summer residents in Availability of biological information in many southern Arizona where effort has been much areas of northern Sonora should increase as more extensive (Monson and Phillips 1981, accessibility is improved and as interest in the Rosenberg and Witzeman 1999, Corman and diversity, uniqueness, and preservation of this Wise-Gervais 2005). These patterns and those in region is enhanced. other areas of western North America (Johnson 1994) and southern Texas (Brush 2005) suggest CONSERVATION AND THREATS some southern species are expanding north- ward possibly in response to changing resource Information on distribution and abundance distributions resulting from climate change and of wildlife is essential for conservation. Without a widening of tropical atmospheric circula- these data, conservation priorities may be mis- tions during recent decades (Seidel et al. 2008). guided and important populations may be lost Although poleward shifts in species distribu- or degraded before they can be managed and tions in response to climate change have been protected. Prospects for conserving, manag- observed on nearly every continent (Parmesan ing, and enhancing populations of landbirds in and Yohe 2003, Root et al. 2003, Parmesan 2006), northern Sonora are promising because human time and additional study are required to fur- population densities throughout much of the ther elucidate these trends in northern Mexico. region are low and because vast areas of natural vegetation remain relatively intact and unfrag- EFFORT—PAST, PRESENT, AND FUTURE mented (Stoleson et al. 2005, Felger et al. 2007). Further, recent federal laws in Mexico have Although my coverage was extensive, it was created a system that could aid landowners in limited in some regions. After comparing my conservation and sustainable use of wildlife fi ndings with those of previous studies, I failed especially once these programs are improved to detect an average of 7% of all species that had and additional resources are provided (Valdez been at least presumed to breed in a watershed et al. 2006, Weber et al. 2006, Sisk et al. 2007). In region, and this quantity varied with effort recent years there has also been an increase in (Tables 1 and 2). Although some species that I activity by private conservation organizations failed to detect may no longer occur, more effort in northern Sonora. These efforts have been especially at high elevations would have pro- led by Biodiversidad y Desarrollo Armónico, duced additional data, particularly in the Santa Naturalia, and The Nature Conservancy in Cruz, Bacanuchi-Sonora, San Pedro, and San northeast Sonora, by Pronatura in northwest Miguel watershed regions. Upper elevations Sonora, and assisted by partnerships with in several mountain ranges in northern Sonora public agencies through organizations such have likely never been visited by ornithologists as Sonoran Joint Venture. When enhanced by including the Sierras San Antonio, San Jose, data on distribution, status, and habitat needs el Chivato, la Madera, Cucurpe, Cubabi, el of landbirds, these efforts can produce valuable Alamo, and San Manuel. Aside from my efforts, results. bird observations at upper elevations in the Despite good prospects for conservation, sig- Sierras el Pinito, Cananea, and los Ajos had not nifi cant threats exist. Loss and degradation of been reported for over fi ve decades (Marshall riparian areas due to agriculture, unsustainable 1957) and other lower yet regionally signifi - grazing practices, and excessive groundwater cant mountains such as the Sierras San Juan pumping are having a profound infl uence on and el Humo had not been visited during the the structure and function of these systems. breeding season. Additional effort in these and Cottonwood forests along the Río Magdalena other areas of northern Sonora will yield new between Magdalena de Kino and Santa Ana and valuable information especially when the have been steadily declining for some time and adjoining Yaqui watershed is considered. no longer occur more than a few kilometers Despite more than a century of ornithological below Magdalena de Kino (A. D. Flesch, pers. work in northern Sonora, Mexico (van Rossem obs.). Riparian forests throughout much of the 1945, Russell and Monson 1998) status and dis- Santa Cruz Valley have been highly degraded tribution of many species had remained little and although conditions are generally better in known in some regions. This is in sharp con- the San Pedro Valley, regeneration of broadleaf trast to neighboring portions of Arizona where trees is limited in many areas. Riparian forest a great deal of historical (Swarth 1914, Brandt along the Río Altar is also declining locally 1951, Phillips et al. 1964) and recent (Monson above Tubutama and especially near Saríc and Phillips 1981, Rosenberg and Witzeman where quantity of surface water declined greatly BREEDING LANDBIRDS IN NORTHERN SONORA MEXICO—Flesch 45 between 2000 and 2007. Other signifi cant threats Swarthout, and Glenn Johnson who surveyed to landbirds in northern Sonora include over- transects and Gabriel Valencia Ortega, Andrés grazing and degradation of grasslands, limited Villareal Lizárraga, Shawn Lowery, Jeremy regeneration of important nest-cavity substrates Russell, Jon Green, and Robert Hunt who con- such large trees and saguaros (Carnegiea gigan- tributed incidental observations. I thank Sky tea), excessive fuel-wood cutting, and urbaniza- Jacobs, Mac Hudson, and Lisa Hahn for com- tion on a local scale (Flesch 2003, Búrquez and panionship in the fi eld. For logistical support Martínez-Yrízar 2007). Grazing intensity in in Sonora, I thank Eduardo Lopez Saavedra northern Sonora is generally much higher than of Biodiversidad y Desarrollo Armónico, in adjacent Arizona (Balling 1988), and if better Jaqueline Garcia Hernandez of Centro de managed could reduce the ecological costs and Investigacion en Alimentacion y Desarrollo, enhance the economic benefi ts of this nearly and Elvira Rojero Diaz and the staff of the ubiquitous land use. Ajos-Bavispe Reserve, Comisión Nacional Cross-border partnerships between govern- de Áreas Naturales Protegidas. I thank Bob ment and non-governmental organizations, sci- Steidl for administrative support and Juan entists, and private citizens have the potential Carlos Bravo and Gerardo Carreón Arroyo to optimize conservation, management, and for Spanish translation. Indirect fi nancial sup- restoration efforts in the borderlands. This need port was provided by of the USDI Fish and for coordination is emphasized by the ecologi- Wildlife Service, National Park Service, and cal connections we share across the border and Arizona Department of Transportation. Direct our joint stake in conserving natural resources fi nancial support was provided by Sonoran for future generations. The international border Joint Venture, T&E, Inc., and mainly through is a political, not a biological boundary and as personal contributions. I thank Glenn Johnson, such, persistence of many populations depends Stephen Russell, and two anonymous review- on the actions and priorities of our two nations. ers for comments on earlier versions of the manuscript. Finally, I thank the people and ACKNOWLEDGMENTS landowners of northern Sonora for welcom- ing us on their lands. This effort is dedicated I am grateful to my fi eld assistants. They to the memory of Benjamin M. Chameides who include Sky Jacobs, Greg Greene, Elliott inspired me to explore.