UNLV Retrospective Theses & Dissertations
1-1-1998
A comparative study of honey mesquite woodlands in southern Nevada and their use by phainopeplas and other avian species
Jeri Brastrup Krueger University of Nevada, Las Vegas
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Repository Citation Krueger, Jeri Brastrup, "A comparative study of honey mesquite woodlands in southern Nevada and their use by phainopeplas and other avian species" (1998). UNLV Retrospective Theses & Dissertations. 843. http://dx.doi.org/10.25669/yjvi-ktl6
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A COMPARATIVE STUDY OF HONEY MESQUITE WOODLANDS IN SOUTHERN
NEVADA AND THEIR USE BY PHAINOPEPLAS
AND OTHER AVIAN SPECIES
by
Jeri Brastrup Krueger
Bachelor of Science Colorado State University 1993
A thesis submitted in partial fulfillment of the requirements for the degree of
Master of Science
in
Biology
Department of Biological Sciences University of Nevada, Las Vegas May 1998
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 139 0646
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thesis Approval The Graduate College University of Nevada, Las Vegas
April 20______, 19 98
The Thesis prepared by
______Jeri Brastrup Krueger
Entitled
A Comparative Study of Four Honey Mesquite Woodlands in
______Southern Nevada and Their Use by Phainopeplas______
and Other Avian Species
is approved in partial fulfillment of the requirements for the degree of
Master of Science
QIacX Examitiation Cotimiitttv Cluiir
Dean of the Cjadlate College I j
Examination Committee Member, -,
Examination Committee Member
Graduate College Faculty Representative
11
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT
A Comparative Study of Honey Mesquite Woodlands in Southern Nevada and Their Use by Phainopeplas and Other Avian Species
by
Jeri Brastrup Krueger
Dr. Charles Douglas, Examination Committee Chair Professor of Biology University of Nevada, Las Vegas
A study of four honey mesquite (Prosopis glandulosa var. torreyana) woodlands
located at Moapa, Stewart Valley, Pah rump, and Stump Spring in southern Nevada was
conducted to 1) describe the current condition of mesquite woodlands, 2) compare avian
community indices among the four sites, and 3) locate breeding Phainopepla populations
and determine breeding season, nesting success, and habitat requirements. Groundwater
was closest to the surface at Stewart Valley, which contained the oldest and largest trees.
Moapa had the greatest avian density and species richness for all species, and greatest
species richness for breeding birds. No differences were detected in species diversity for
all species and for breeding species only among the four sites. Moapa was the only site
that supported a Phainopepla breeding population. Phainopepla selected larger trees
111
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with fewer stems and heavy Phoradendron infection for nesting sites, and breeding
success was reduced when birds nested lower in the tree and did not build nests within the
protection of a Phoradendron clump.
IV
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS
ABSTRACT...... iii
LIST OF TABLES ...... vii
LIST OF FIGURES ...... viii
ACKNOWLEDGEMENTS...... x
CHAPTER I INTRODUCTION...... I History and Status of Prosopis (Honey Mesquite) in the Southwestern United States ...... 1 The Role of Prosopis as Avian H a b itat...... 5 An Overview of the Ecology and Status of Phainopepla nitens...... 8 Objectives and Hypotheses ...... 11 Literature Cited ...... 15
CHAPTER 2 A COMPARISON OF STRUCTURAL CHARACTERISTICS FOR FOUR Prosopis (HONEY MESQUITE) WOODLANDS IN SOUTHERN NEVADA ...... 24 Introduction ...... 24 Materials and Methods ...... 27 Results and Discussion ...... 34 Literature Cited ...... 52
CHAPTER 3 AVIAN USE OF FOUR Prosopis (HONEY MESQUITE) WOODLANDS IN SOUTHERN NEVADA ...... 58 Introduction ...... 58 Materials and Methods ...... 61 Results and Discussion ...... 62 Literature Cited ...... 72
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4 BREEDING SUCCESS AND NEST SITE SELECTION OF Phainopepla nitens IN A SOUTHERN NEVADA Prosopis W OODLAND...... 76 Introduction ...... 76 Materials and Methods ...... 78 Breeding Season and Nesting Success ...... 78 Nest Site Selection ...... 79 Results and Discussion ...... 81 Breeding Season and Nesting Success ...... 81 Nest Site Selection ...... 85 Management Implications ...... 92 Literature Cited ...... 93
CHAPTER 5 THESIS SUMMARY ...... 96 Conclusions ...... 96 Management Recommendations ...... 98
APPENDK I MISTLETOE RATING SYSTEM ...... 101
APPENDIX n SOIL pH, MINERAL, AND NITROGEN CONTENT ...... 104
APPENDK m LIST OF AVIAN SPECIES ...... 105
APPENDK IV NEST OBSERVATIONS OF Phainopepla nitens...... 113
BIBLIOGRAPHY ...... 122
VTTA ...... 134
VI
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES
Table 2-1 Soil textures determined from soil samples obtained at 1.5-m intervals from water well drilling at four Prosopis woodland sites in southern Nevada ...... 44 Table 3-1 Results of three-way ANOVA including site by month and site by year interactions for all bird species surveyed from February through June of 1996 and 1997 within four Prosopis woodland sites in southern Nevada ...... 64 Table 3-2 Results of three-way ANOVA including site by month and site by year interactions for breeding bird species surveyed from March through June of 1996 and 1997 within four Prosopis woodland sites in southern Nevada ...... 64 Table 4-1 Nest survival probabilities ofPhainopepla nitens for 1996 and 1997 at Moapa, Clark County, N e v a d a ...... 84 Table 4-2 Two-sample t-tests comparing Phainopepla nest site characteristics with overall woodland characteristics at Moapa, Clark County, N evada ...... 86 Table 4-3 Two-sample t-tests comparing Phainopepla nest tree characteristics with those of randomly selected trees at Moapa, Clark County, N evada ...... 86 Table 4-4 Pearson correlation coefficients for tree structural characteristics of Phainopepla nest trees and random trees at Moapa, Clark County, N evada ...... 87 Table 4-5 Observed and expected values for random trees and Phainopepla nest trees for four tree structural categories at Moapa, Clark County, N evada ...... 90 Table 4-6 Bonferroni 90% simultaneous confidence intervals for the difference in four tree structural categories between random trees and Phainopepla nest trees at Moapa, Clark County, N evada ...... 90
VII
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF HGURES
Figure 2-1 Locations of four Prosopis woodland sites in southern Nevada ...... 28 Figure 2-2 Linear regression of static water levels and year wells were drilled in the vicinity of three Prosopis woodland sites in southern Nevada ...... 35 Figure 2-3 Differences in site characteristics of four Prosopis woodlands in southern Nevada ...... 37 Figure 2-4 Differences in tree characteristics of four Prosopis woodlands in southern Nevada ...... 39 Figure 2-5 Age class distribution of Prosopis woodland study sites in southern Nevada ...... 40 Figure 2-6 Proportional distribution of Phoradendron infection ratings by class at four Prosopis woodland sites in southern Nevada ...... 41 Figure 2-7 Groundwater levels determined from the installation of monitoring wells at four Prosopis woodland sites in southern Nevada ...... 43 Figure 3-1 Comparison of avian community indices for all bird species surveyed within four Prosopis woodland sites in southern N evada ...... 65 Figure 3-2 Comparison of avian community indices for breeding birds surveyed within four Prosopis woodland sites in southern N evada ...... 66 Figure 3-3 1996 and 1997 monthly averages of avian community indices for all bird species observed in four Prosopis woodlands in southern Nevada ...... 68 Figure 3-4 1996 and 1997 monthly averages of avian community indices for breeding bird species observed in four Prosopis woodlands in southern Nevada ...... 69 Figure 4-1 Number of nests under observation within each nesting stage during the 1996 Phainopepla breeding season at Moapa, Clark County, Nevada ...... 83 Figure 4-2 Number of nests under observation within each nesting stage during the 1997 Phainopepla breeding season at Moapa, Clark County, Nevada ...... 83 Figure 4-3 Proportional differences in Phoradendron infection class between Phainopepla nest trees and random trees at Moapa, Clark County, N evada ...... 87
VllI
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4-4 Relationship between tree height and stems per tree for nest trees and random trees at Moapa, Clark County, N evada ...... 89
IX
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS
Funding for this project was provided by Clark County as part of the multi-species
component of the Desert Conservation Plan for the desert tortoise. This project was
developed as part of an Interlocal Agreement between Clark County and the Bureau of
Land Management (BLM), Las Vegas Field Office. I would like to thank the BLM for
providing vehicles, office space, and computer equipment. Special thanks is offered to
Sidney Slone, who assisted in developing the idea for the project. I am also grateful to
Paul Summers who supervised the drilling of observation wells. I would also like to
thank Gayle Marrs-Smith for her assistance in plant identification, Jeanie Cole and
Michelle Berkowitz for their help in locating nests, and the three field assistants who
worked tirelessly in thorny mesquite habitat during the heat of the summer.
I would like to thank the Maijorie Barrick Museum of Natural History for their
help in bird identification, Tom Harlan who is affiliated with the University of Arizona
Laboratory of Tree Ring Research for his help and expertise in mesquite tree-ring
analysis, the Bureau of Reclamation, Yuma, Arizona for the drilling of water wells, and
Utah State University Analytical Labs for analysis of soil samples.
I am especially grateful to my advisor. Dr. Charles Douglas, for his guidance and
advise throughout the development and implementation of this project. I would also like
to thank the other members of my committee. Dr. Stan Smith, Dr. Donald Baepler, and
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dr. Evangelos Yfantis, for their editorial comments on the manuscript, ideas for design,
and suggestions on statistical analysis.
Most of all, I would like to thank my mother, Sally, for being the strong
foundation I needed to see me through good times and bad, and for her unending support
and encouragement during my mid-life career change and many years of college, and my
father, the late D.R. (Bob) Brastrup, who instilled and nurtured in me a respect and
appreciation of wildlife. It is to my mother and the memory of my father that I dedicate
this thesis.
XI
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I
INTRODUCTION
History and Status of Prosopis (Honey Mesquite) in the
Southwestern United States
Prosopis (mesquite) is a woody shrub or tree of the Fabaceae family found in arid
and semi-arid climates around the world. Three species of Prosopis occur in the
southwestern United States (Fisher 1977): Prosopis glandulosa (honey mesquite), P.
velutina (velvet mesquite), and P. pubescens (screwbean mesquite). Members of the
genus Prosopis are generally classified as phreatophytes, which are plants that tap into
groundwater (Meinzer 1927). Prosopis glandulosa occurs in Texas, northern Mexico,
and the southern parts of New Mexico, Arizona, Nevada, and California (Simpson and
Solbrig 1977). Prosopis velutina is found in southwestern Arizona and northwestern
Mexico, and is distinguished from P. glandulosa by its small, velvety leaves and beaded
or speckled pods (Burkart and Simpson 1977). Eastern populations of honey mesquite
(P. glandulosa var. glandulosa) are separated from western populations (P. glandulosa
var. torreyana) by the Pecos River, and can be distinguished by the smaller leaves and
longer fruits of the western variety (Hilu et al. 1982). Southern Nevada contains a portion
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of the northern limit of the range of P. glandulosa var. torreyana, which is the focus of
this study.
The root system of Prosopis consists of shallow lateral roots, which are used for
uptake of nutrients and shallow soil moisture, and large taproots, which are able to grow
to great depths to reach groundwater (Jenkins et al. 1987, Meinzer 1927, Phillips 1963,
Rundel et al. 1982). Lateral roots allow Prosopis to survive in areas with moderate
precipitation where groundwater is less available, while the taproot enables Prosopis to
exist in arid environments where precipitation and soil moisture are low. The extent to
which each root system is developed depends upon the availability of surface water or
groundwater. Lateral roots tend to be more developed in areas with greater availability of
surface soil moisture, while taproots become more developed in areas with greater
abundance of subsurface water (Ansley et al. 1990, Cannon 1913, Heitschmidt et al.
1988).
The lateral root system of Prosopis has allowed it to become uncoupled from the
requirement of a permanent groundwater source in the semi-arid parts of its range, and in
the late 1800's Prosopis began spreading into the grasslands and savannas of Texas and
New Mexico (Wright 1982, Wright et al. 1976). Overgrazing by livestock and fire
suppression were identified as the main factors responsible for the spread of Prosopis
(Wright et al. 1976). Reduced competition with grasses allows Prosopis seedlings to
sprout (Van Auken and Bush 1989), and periodic fires that previously restricted the
growth and spread of Prosopis were eliminated (Wright et al. 1976). Livestock are also
excellent vectors for Prosopis seed dispersal. Prosopis pods are highly desirable forage.
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and the seeds pass through the gut unharmed and are spread through droppings (Wright
1982). In addition, trampling of Prosopis caused the formation of multi-stemmed shrubs
occupying a larger basal area than the original single-stemmed tree (Fisher 1977). The
subsequent decline in grassland productivity led to the study of methods to eradicate
Prosopis, which had become known as a pest in the semi-arid portions of its range (Cable
and Tschirley 1961, Fisher et al. 1946, Goen and Dahl 1982, Humphrey 1949, Scifres et
al. 1973, Ueckert et al. 1971).
In contrast, the arid climate of the western portion of its range has restricted
Prosopis to areas with shallow groundwater (Nilsen et al. 1984b, Stromberg et al. 1992).
Southern Nevada Prosopis are typically found growing in deep soils along riparian areas,
washes, and the edges of dry lake beds where their well-developed taproots can penetrate
into subsurface water. The growth form of Prosopis can range from a shrub to tall trees
reaching 12 m in height and stems approaching 1 m in diameter (Meinzer 1927). It has
been observed that the size of Prosopis is an indication of groundwater depth (Cannon
1913, Jaeger 1983). Prosopis occurs as a tree in areas where groundwater is relatively
close to the soil surface, and decreases in size as distance to the water table increases
(Stromberg et al. 1993). Prosopis is an extravagant water user under conditions of
abundant water supply (Ansley et al. 1992), which has allowed Prosopis to maintain high
summer productivity despite high temperatures and low precipitation (Nilsen et al. 1981).
However, transpiration and stomatal conductance are reduced as water availability
declines (Hanson 1982, Robinson 1958, Easter and Sosebee 1975) and more resources are
allocated to root growth and fruit production (Lee and Felker 1992, Nilsen et al. 1986,
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Nilsen et al. 1987), resulting in a decrease in size and aboveground productivity (Meinzer
1927, Wan and Sosebee 1991). In addition, there is a limit as to how deep Prosopis roots
will grow to reach groundwater (Meinzer 1927), and it becomes increasingly difficult for
Prosopis to survive once the water table falls below 15 m (Judd et al. 1971).
The requirement of a permanent, reliable water source has placed southern
Nevada Prosopis populations in direct competition for scarce water supplies with a
growing human population that is also dependent on the availability of groundwater.
Clark County, within which Las Vegas is located, experienced a ca. 40% population
increase between 1990 and 1996, and is projected to more than double by 2015 (Sources:
U.S. Bureau of the Census, Washington, DC and Nevada State Demographer’s Office,
Reno, NV). Nye County, which contains the unincorporated town of Pah rump, as well as
one of southern Nevada’s largest remaining complexes of Prosopis woodlands, sustained
a ca. 45% population increase for the same time period (Source: U.S. Bureau of the
Census, Washington, DC). A report by the U.S. Geological Survey on groundwater
depletion determined that groundwater pumping in Pahrump Valley had caused an
overdraft of 11,000 acre-feet per year (Harrill 1982).
Much of Las Vegas Valley’s Prosopis woodlands has been lost due to urban
growth, and southern Nevada’s remaining woodlands are threatened with increasing
disturbance from a growing human population. In addition to the effects of groundwater
depletion, mechanical or physical damage to the stem can also affect Prosopis growth
form (Mooney et al. 1977). Damage from wood-cutting, fire, freezing temperatures,
herbivory, and trampling promotes resprouting and transforms open groves of trees into
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short, dense thickets (Fisher 1977, Heitschmidt et al. 1988). Decreasing water tables and
increased frequency of fire and herbivory can also reduce successful seedling
establishment (Nilsen et al. 1987, Rorabaugh 1995, Wright and Bailey 1982).
Less than 2% of the land area in the Southwest is composed of woodland
vegetation (Stromberg et al. 1993), of whichProsopis is a major component. Prosopis
woodlands are difficult to replace once destroyed. It takes over 100 years for a mature
Prosopis woodland to develop and requires a specific set of environmental events that
occur infrequently in an arid climate (Minckley and Clark 1984, Mooney et al. 1977).
Desert woodlands contribute disproportionately to the biological diversity of the desert
(Stromberg et al. 1993), providing food, shelter, and breeding sites for a variety of species
within an otherwise inhospitable environment (Simpson and Neff 1977). The nitrogen-
fixing properties of Prosopis creates fertile islands where other plants and animals can
obtain nitrogen in a system that is for the most part nitrogen deficient (Farnsworth et al.
1978, Jenkins et al. 1987, Tiedemann and Kiemmedson 1986, Virginia and Jarrell 1983,
W est and Kiemmedson 1978). The dense wood of Prosopis is highly valued for its use in
heating, barbeque grilling, furniture, flooring, and wood-carving (Comejo-Oviedo et al.
1992, Felger 1977, Haller 1980), and its utility as an aridland crop has recently been
studied (Cline et al. 1986, Nilsen et al. 1984a).
The Role of Prosopis as Avian Habitat
In a landscape dominated by desert scrub the patchy occurrence of Prosopis
woodlands serves as important breeding and resting places for many avian species.
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Woodlands offer protection from weather and predators and provide places where birds
have a more favorable energy budget. Desert woodlands comprise a small percentage of
the total vegetation in the southwest, but support greater densities of birds than the
surrounding desert habitat (Germano et al. 1983, Laudenslayer 1981, Szaro 1981).
Woodlands add structural complexity to the landscape, providing more nesting sites and
food resources for breeding birds. Several species of desert breeding birds such as
Vermivora luciae (Lucy’s Warbler) and Phainopepla nitens (Phainopepla) nest almost
exclusively in Prosopis (Anderson and Ohmart 1978, Meents et al. 1983). Prosopis
woodlands are also important stopover sites for migratory birds. Several studies have
discussed the importance of stopover sites for migrants (Kuenzi and Moore 1991, Moore
et al. 1990, Rappole and Warner 1976) and have noted that degradation or loss of
stopover habitat can severely reduce the chance of a successful migration (Terborgh
1989). Many neotropical migrants cannot store enough fat to support them throughout
their entire migration, and must stop periodically to rest and replenish energy reserves
(Winker et al. 1992). Patches of Prosopis scattered throughout the desert may play an
important role in the successful migration of birds attempting to cross large ecological
barriers such as deserts (Berthold and Terrill 1991).
Phoradendron califomicum (desert mistletoe) is a parasitic plant that uses
Prosopis as its host (Tinnin et al. 1971). Phoradendron produces lush crops of berries
that many desert birds rely on for food (Cowles 1972, Overton 1993). Phoradendron
flowers in the spring, and berries start forming in early fall (Cowles 1936, Walsberg
1977). The berries, which have high lipid content, tend to persist on the plant until the
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following May or June, and provide wintering birds and early breeders with a nutritious
and dependable food supply (Snow and Snow 1988). Moisture from berries can also
provide birds with enough water to survive in an environment devoid of other water
resources (Crouch 1943, Hensley 1954, Walsberg 1975).
The structure of Prosopis woodlands in the southwestern deserts largely depends
on the availability of groundwater. Large trees can be found growing along riparian
corridors, drainages, and dry lake beds where groundwater is more plentiful, whereas
Prosopis adopts a shorter, shrubby growth form as distance to the water table increases
(Cannon 1913, Jaeger 1983). Expanding human populations in the Southwest have
placed more demand on groundwater resources, resulting in declining water table levels
(Harrill 1982, Stromberg et al. 1992) and changes in Prosopis growth form and survival
(Stromberg et al. 1993). In turn, changes in structure of Prosopis woodlands may
significantly alter its effectiveness as wildlife habitat. The relationship between avian
communities and the structure of their habitat has been well-studied, and it is generally
known that species abundance and diversity increase as habitat volume and complexity
increase (Hansen et al. 1995, James 1971, Mac Arthur 1965, Mac Arthur and Mac Arthur
1961, Rotenberry 1985, Rotenberry and Wiens 1980). However, the use of density and
diversity indices has been criticized in the past (James and Rathbun 1981, Van Home
1983), and results from several studies have found inconsistent relationships between bird
density/diversity and vegetation structure (Baida 1969, Carothers et al. 1974, Rice et al.
1984, Willson 1974). It has been noted that in some situations species may be responding
to factors other than vegetation structure (Irwin 1994). MacArthur (1964) commented
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that, especially in western habitats, birds may respond more strongly to the presence of
water than to habitat structure. In addition, frugivores may key on abundance of fruit
rather than specific vegetation profiles (Rice et al. 1983). Others have noted that the use
of complex diversity indices such as Shannon-Weiner (see Shannon and Weaver 1963)
hide important information that could be more easily portrayed by the use of simpler
indices such as species richness and density (James and Rathbun 1981, Mills et al. 1991).
An Overview of the Ecology and Status of Phainopepla nitens
Phainopepla nitens (phainopepla) is a frugivorous songbird found only in the
southwestern United States and Mexico (American Ornithologists’ Union 1983). Its
name is derived from the Greek words meaning “shining robe”, which describes the
glossy black plumage of males (Terres 1995). Both males and females have crests, bright
red irises, and white wing patches, but can be distinguished from each other by the
female’s gray color. Phainopepla is the only member of the Ptilogonatidae (Silky
Flycatcher) family found in the United States. Its range extends from the Mexican
Plateau north into Arizona, California, extreme western Texas, and the southern regions
of Nevada and New Mexico (Walsberg 1977).
During the year, Phainopepla shifts its distribution between two very distinct
habitat types. In winter and early spring Phainopepla populations breed in the lower
elevations of the Sonoran and Mojave Deserts, where they feed on the berries of
Phoradendron califomicum (desert mistletoe) that parasitize plants of the Fabaceae
family including Prosopis spp. (mesquite).Acacia greggii (catclaw acacia), Cercidium
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floridum (palo verde), and Olneya tesota (ironwood) (Anderson and Ohmart 1978,
Crouch 1943, Overton 1993). The specialized digestive tract ofPhainopepla is an
example of its adaptation to a nearly exclusive diet of Phoradendron berries (Walsberg
1975). The breeding season occurs from February through the end of April or beginning
of May, at which time they disperse to cooler regions located to the west, east, and north
(Walsberg 1977). In summer Phainopepla is known to breed in the Sierra Nevada oak
foothills and coastal mountains of California where they nest in oaks, sycamores, and
orchards and feed on the fruits of a variety of plants including Rhamnus crocea
(buckthorn), Sambucus mexicana (elderberry), Ribes malvaceum (chaparral currant),
Comarostaphylis diversifoba (summer holly) and Schinus molle (peppertree) (Walsberg
1977, Woods 1965). Walsberg (1977) observed dramatic differences in territorial
behavior between the two habitat types. Desert breeders fiercely defend territories
averaging 0.4 ha in size that encompass both the food source and the nest site. Summer
breeders in California typically nest in habitats where the food source is located farther
away from nesting sites, and smaller territories averaging 0.03 ha in size include only the
nest tree.
It has been suggested that the same birds nest in both habitats in a single year
(Woods 1965). Dual nestings in two different habitats are extremely rare (Walsberg
1978), and many doubt its occurrence (Gilman 1903, Grinnell 1914, Miller 1933).
However, Walsberg (1977) noted evidence of a dual breeding cycle in May 1973 when he
sighted a Phainopepla within a breeding population in a southern California oak
woodland that he had banded in March while it was breeding in the desert. Walsberg
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then admitted the circumstantial nature of the evidence and stated that data were
insufficient to reach a definite conclusion. Nevertheless, statements alluding to
Phainopepla's dual breeding cycle can be found in current articles, books, and field
guides (see Harvey 1994, National Geographic Society 1987, Terres 1995).
Phainopepla's dependence on Phoradendron has been well documented (e.g.
Hensley 1954, Laudenslayer 1981, Rand and Rand 1943, Snow and Snow 1988), but little
is known about the stmctural component of its habitat in the desert. It has been observed
that its favorite perch is the uppermost branches of trees, where it has an unobstructed
view of the area for territorial and predator defense (Jaeger 1983). Tall trees can also
assist Phainopepla's habit of hawking insects, a behavior common among members and
close relatives of the flycatcher families (Cowles 1972). Walsberg (1977) also noted
Phainopepla's emphasis on visual display, which is reflected in its color and morphology.
The conspicuousness of the crest, white wing patches, and long tail assist in
Phainopepla's territorial advertisement, but are most effective in open habitats with
available high perches. AlthoughPhainopepla is known to nest in a variety of
leguminous trees and shrubs, Overton (1993) determined that Prosopis was a favored
perch, Cercidium was an avoided perch, and Acacia was a neutral perch. Overton
attributed these differences to differences in tree structure. Prosopis was typically taller
with stiff branches and an open crown, whereas Acacia was shorter, and Cercidium
contained weaker branches with a broom-like canopy.
The studies of Walsberg have added much to our knowledge of the ecology and
energetics of PJiamopcp/a (see Walsberg 1975, 1977, 1978, 1982, 1983, 1986), but little
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is known about the genetic structure and migration patterns of populations. Southern
Nevada contains a portion of the northern periphery of Phainopepla's range (Walsberg
1977), as well as that of Prosopis (Simpson and Solbrig 1977). It is often assumed that
peripheral populations are sinks that occur in marginal habitat, and are not particularly
important in the survival of the species as a whole (see Lomolino and Channell 1995).
Few studies have focused on Phainopepla in Nevada because it is considered a peripheral
population in Nevada and is abundant in other parts of its range (Jones 1990, unpubl.
report). However, Phainopepla is closely linked to the food source in its desert habitat,
and its existence is associated with the quality and quantity of the habitat (Meents et al.
1984). Degradation or loss of Prosopis woodlands in southern Nevada may adversely
affect Phainopepla populations, resulting in a reduction of its existing range. It has also
been observed that some populations follow a local altitudinal migration rather than an
expansive latitudinal migration (see Woods 1965), which may lead to more genetically
distinct populations. Recent studies have discussed the significance of peripheral
populations as centers of genetic divergence and spéciation (Davidson et al. 1996, Furlow
and Armijo-Prewitt 1995, Lesica and Allendorf 1995, Lomolino and Channell 1995),
which supports the importance of Phainopepla populations in southern Nevada.
Objectives and Hypotheses
The purpose of this study was to describe the current condition of four Prosopis
woodlands in southern Nevada, and determine their effectiveness as habitat for
Phainopepla and other avian species. The woodlands were located on public lands
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12
administered by the Bureau of Land Management. Current knowledge of the condition of
Prosopis woodlands and the status of Phainopepla populations in southern Nevada is
limited. Therefore, the following objectives and hypotheses were developed to determine
the current health and vigor of Prosopis woodlands in southern Nevada, and assist the
BLM and other agencies in development of a mesquite habitat management plan:
1. Describe the general health and vigor of Prosopis woodlands, and determine the
influence of water table level on Prosopis growth. The comparison of tree
structural characteristics, age class distribution, and water table level among
woodlands should reflect the relative health and vigor of the woodlands.
Hypotheses:
(1) Prosopis woodlands located in areas where groundwater is closer to the
surface should contain larger, taller trees than those located in areas with
deeper groundwater levels.
(2) Healthy woodlands should show less sign of stress and disturbance, and
should contain larger trees with fewer stems.
(3) Healthy woodlands should also show signs of recruitment, reflected by a
more even distribution of age class.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13
2. Describe avian communities in Prosopis woodlands, and determine if woodland
conditions reflect differences in avian density, species richness, and species
diversity. All three indices were used so as to compare their usefulness as avian
community indicators within monospecific stands of Prosopis.
Hypotheses:
(1) Avian density, species richness, and species diversity should be greater
within healthy woodlands with larger trees than within woodlands exposed
to more stress and disturbance.
(2) If avian communities respond to changes in vegetation structure, then
comparison of the three avian indices among the four woodlands should
reflect differences in woodland growth form.
3. Document the occurrence of breeding Phainopepla populations, and determine
breeding season, nesting success, and habitat requirements. Identification of
successfully breeding Phainopepla populations within Prosopis woodlands will
add to our knowledge of the status of Phainopepla in southern Nevada.
Determination of breeding season, nesting success, and habitat requirements will
help land managers understand how to best manage Prosopis woodlands for
Phainopepla habitat. If Phainopepla's preference for certain structural
characteristics improves breeding success, then management should concentrate
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14
on maintaining and improving the presence of these characteristics within
Prosopis woodlands in southern Nevada.
Hypothesis:
Phainopepla should nest in larger, taller trees with heavy Phoradendron
infection, which in turn should increase Phainopepla breeding success.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2
A COMPARISON OF STRUCTURAL CHARACTERISTICS FOR
FOUR Prosopis (HONEY MESQUITE) WOODLANDS
IN SOUTHERN NEVADA
Introduction
Prosopis glandulosa var. torreyana (western honey mesquite) is a phreatophytic
woody shrub or tree found in the southwestern United States. Its range extends from
western Texas to southern California and northwestern Mexico, including the southern
portions of New Mexico, Arizona, and Nevada (Simpson and Solbrig 1977). The western
variety is separated from its eastern relative (P. glandulosa var. glandulosa) by the Pecos
River, and can be distinguished from eastern populations by its smaller leaves and longer
fruits (Hilu et al. 1982).
The root system of Prosopis consists of shallow lateral roots, which are used for
uptake of nutrients and shallow soil moisture, and large taproots, which are able to grow
to great depths to reach groundwater (Jenkins et al. 1987, Meinzer 1927, Phillips 1963,
Rundel et al. 1982). Lateral roots allow Prosopis to survive in areas with moderate
precipitation where groundwater is less available, while the taproot enables Prosopis to
exist in arid environments where precipitation and soil moisture are low. The extent to
24
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which each root system is developed depends upon the availability of surface or ground
water (Cannon 1913). Lateral roots tend to be more developed in areas with greater
availability of soil moisture, whereas Prosopis relies more on well-developed taproots for
water uptake in areas with less available soil moisture and greater abundance of
subsurface water (Ansley et al. 1990, Heitschmidt et al. 1988).
Prosopis populations occurring in semi-arid climates rely more on their lateral
root system for water uptake, and are thus uncoupled from the requirement of a
permanent groundwater source (Cable 1977). This has allowed Prosopis to spread into
the grasslands and savannas of Texas, New Mexico, and Arizona where past over-grazing
and fire suppression have disrupted the natural balance of the ecosystem (Archer 1989,
Fisher 1977, Wright 1982). As a consequence, much of the available literature on
Prosopis has focused on its eradication (Cable and Tschirley 1961, Fisher et al. 1946,
Goen and Dahl 1982, Humphrey 1949, Scifres et al. 1973, Ueckert et al. 1971). In
contrast, high temperatures and low precipitation in arid regions such as southern Nevada
have confined the distribution of Prosopis to areas where groundwater is accessible
(Nilsen et al. 1981). In southern Nevada, temperatures can range from a maximum of
48°C in summer and a minimum of -5°C in winter. Average annual precipitation is 10-15
cm, with the majority commonly supplied by infrequent, individual storms. Prosopis
woodlands in southern Nevada are typically found growing in deep soils along riparian
areas, washes, and the edges of dry lake beds where their well-developed taproots can
penetrate into subsurface water.
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The requirement of a permanent, reliable water source has placed southern
Nevada Prosopis populations in direct competition for scarce water supplies with a
growing human population that is also dependent on the availability of shallow
groundwater. Clark County, within which Las Vegas is located, experienced a ca. 40%
population increase between 1990 and 1996, and is projected to more than double by
2015 (Sources: U.S. Bureau of the Census, Washington, DC and Nevada State
Demographer’s Office, Reno, NV). Nye County, which contains the unincorporated town
of Pahrump, as well as one of southern Nevada’s largest remaining complexes of
Prosopis woodlands, sustained a ca. 40% population increase for the same time period
(Source: U.S. Bureau of the Census, Washington, DC). Pahrump lies within the Pahrump
Valley Hydrographic Basin, which is an internal drainage system. The Spring Mountains
to the east are the source for virtually all the area’s water supply (Harrill 1982). A study
on groundwater depletion in Pahrump Valley between the years 1962 and 1975
determined that as of 1975 groundwater pumping was causing an overdraft of 11,000
acre-feet per year (Harrill 1982).
Much of Las Vegas Valley’s Prosopis woodlands has been lost due to urban
growth; the remaining woodlands are threatened with increasing disturbance from human
use, including uncontrolled wood-cutting, declining water tables, herbivory, trampling,
and increased fire frequency. Prosopis growth and survival declines as distance to the
water table increases (Cannon 1913, Haas and Dodd 1972, Holland 1987, Judd et al.
1971, Minckley and Clark 1984, Robinson 1958, Stromberg et al. 1993) and extensive
damage to the main stem can change the structure of a woodland from large, single
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stemmed trees to short, dense, multi-stemmed thickets (Fisher 1977, Heitschmidt et al.
1988).
The objectives of this study were to describe the condition of four of southern
Nevada’s remaining Prosopis woodlands, and to detemiine factors responsible for
differences in structural characteristics among the four sites. It was hypothesized that
woodlands located in areas with shallow groundwater levels should contain larger trees
than woodlands located in areas with deeper groundwater levels.
Materials and Methods
Four study sites were selected within monospecific stands of Prosopis glandulosa
var. torreyana (western honey mesquite) in the eastern Mojave Desert of southern
Nevada (Fig. 2-1). All four study sites were located on public lands administered by the
Bureau of Land Management (BLM) and supported Prosopis populations with a tree-like
growth form that occupied areas along the edges of playas and dry washes. No surface or
flowing water was present at any of the sites.
The Moapa site is located three km north of the community of Glendale, Nevada
in Clark County (36°42'N, 114°36'W; 470 m elevation). The Prosopis woodland occupies
a 15-ha area along, and 300 m east of. Meadow Valley Wash. The woodland is
comprised of a sparse understory of Haplopappus acradenius var. erimophilous
(goldenweed) , Lycium cooperi (wolfberry), Elymus cinereus (wild ryegrass), and Vulpia
octiflora (six-weeks fescue). Suaeda torreyana (seepweed) and Salsola paulsenii
(Russian thistle) occur along the edge of the woodland. Salt scrub consisting mainly of
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Lincoln Countv Clark County
F ahrump Las Vegas
Fig. 2-1. Locations of four Prosopis woodland sites in southern Nevada. MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29
Atriplex canescens (four-wing saltbush) occurs to the west of the woodland, and Larrea
tridentata (creosotebush) dominates the landscape to the east. Two irrigated agricultural
fields occur west of the woodland. The soil in the general vicinity is a deep, fine sandy
alluvium derived from sandstone (Bagley 1980). Soil permeability is high and water
capacity is low. The woodland lies within a livestock grazing allotment and the area has
been exposed to both past and present wood-cutting activity and fires.
The Stewart Valley site is located 10 km northwest of the community of
Pahrump, Nevada in Nye County (36°I8'N, 1 lô^HW ; 745 m elevation). The valley is
flanked by the Resting Spring Range to the west and High Peak Mountain to the east.
The woodland runs north-south along the eastern edge of a playa for 5 km. The entire
woodland is approximately 20 ha in size, with the mid one-third occurring on private
land. The woodland supports an understory of Elymus interspersed with patches of
Distichlis spicata (saltgrass). Surrounding vegetation is salt scrub consisting mainly of
Atriplex confertifolia (shadscale) and A. lentiformis (quailbush). About 800 m east of the
woodland the salt scrub is replaced by Larrea. In general, the soils are clay loams that are
deep and moderately well-drained. Permeability is low to moderate and water capacity is
high. The woodland does not lie within a grazing allotment; however, there is evidence
of exposure to fires and recent wood-cutting activity.
The Pahrump site lies on the southwestern edge of the community of Pahrump,
Nevada in Nye County (36°06'N, I16°W; 775 m elevation). This site is part of a larger
complex of linear Prosopis woodlands that follow the east-west drainage pattern in
Pahrump Valley. The site encompasses one Prosopis “stringer” that is 2.1 km long and 9
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ha in size. The understory consists mainly of Bromus rubens (red brome) interspersed
with patches of Elymus. Suaeda and Chrysothamnus spp. (rabbitbrush) occur along the
edge of the woodland, along with A. confertifolia, A. lentiformis, and A. canescens that
also comprise the surrounding desert salt scrub vegetation. Soils are generally deep clay
loams and are similar to those found at the Stewart Valley site. The Pahrump site does
not occur within a grazing allotment but receives frequent human use, including heavy
wood-cutting activity, due to its close proximity to Pahrump.
The Stump Spring site is located 19 km southeast of Pahrump in Clark County,
Nevada (35°54'N, 115°48'W; 865 m elevation). The woodland follows a deeply eroded
wash that runs from the northeast to the southwest for about 3 km. Sampling was
conducted within a one-km-long stretch of woodland encompassing 9 ha. The understory
contains a patchwork of salt scmb species including A. lentiformis, A. canescens, and A.
polycarpa (cattle spinach) along with Chrysothamnus, Suaeda, and Lycium. Lepidium
frem ontii (pepper grass), Gutierrezia sarothrae (snakeweed), Stanleya pinnata (prince’s
plume), and Pulchea sericea (arrow weed) grow in and along the edge of the wash, and
patches of Tamarix ramosissima (saltcedar) have invaded portions of the wash. The
surrounding area is dominated by salt scrub with a secondary component consisting of
Larrea interspersed with Ephedra nevadensis (Mormon tea). The Stump Spring site also
contains several widely spaced, remnant patches of Populus fremontii (Fremont
cottonwood) and Salix goodingii (Gooding’s willow), all of which are dead, dying, or in a
state of severe stress. Surface water once flowed at this site, and was documented in a
diary recorded by the southwestern explorer John C. Fremont (see Fremont 1845) who
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forged the southern Nevada portion of the Old Spanish Trail. Stump Spring apparently
was a resting place for those traversing the Trail through southern Nevada. Subsequently,
part of the area has been designated as a site of cultural significance (Myhrer et al. 1990).
Soils are generally very deep, well-drained fine sandy loams that formed in alluvium and
reworked lacustrine sediments (from U.S. Dept, of Agric. Natural Resources
Conservation Service, Clark County Soil Survey, 1996). The woodland lies within a
grazing allotment that had been heavily grazed in the past but has not been grazed in
recent years. Stump Spring is the most remote of the four sites and has limited access by
road. Woodcutting has not occurred recently at Stump Spring to the extent that it has at
the other three sites, and has been confined to a few small areas of the stand with direct
road access.
Vegetation sampling was conducted between June and August 1996. Rectangular
plots 0.1 ha in size (20 m x 50 m) were placed within each woodland. Location of each
plot was selected randomly along a transect line following the edge of each woodland.
The number of plots (or samples) was determined by the size of each woodland (Moapa =
15; Stewart Valley = 10; Pahrump = 12; Stump Spring = 10), so as to ensure that at least
10% of each site was sampled. Trees within each plot were assigned to one of four age
classes: seedling (trees no more than one m tall), sapling (trees taller than one m with
smooth bark), mature (trees with rough bark), and dead trees. Each tree was measured for
the following characteristics: tree height, canopy spread, canopy volume, stem size, and
intensity of Phoradendron infection. Tree height was determined by the use of a lO-m
extendable fiberglass surveying rod, and measured from the base of the tree to the highest
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point of the live crown. Canopy spread was determined by measuring the greatest length
of the canopy and the width of the canopy perpendicular to the greatest length. These
measurements were converted to m^ by using the equation:
Area = n{Vz \ * Vz w).
Canopy volume was determined by measuring the height of the canopy and then
calculating the volume of one-half of an oblate sphere:
Volume = 4/3 u (Vi 1 * Vz w * ht) / 2
(Gadzia and Ludwig 1983). Diameter of all primary stems was measured with a dbh tape
or calipers at or close to ground level. This was necessary due to the multi-stemmed
growth form ofProsopis. Intensity of Phoradendron infection was determined by using
an adaptation of F. G. Hawksworth’s dwarf mistletoe rating system (Hawksworth 1977,
Dooling 1978). Each tree was visually divided in half vertically. Each side of the tree
was given an infection rating that was assigned to one of four classes: 0 = no infection; 1
= light infection; 2 = moderate infection; 3 = heavy infection. Definitions and
photographs of classes are found in Appendix I. The ratings for each side of the tree were
added to give a rating system ranging from 0 (no infection) to 6 (heavy infection).
Using methods described in Johnson and Wichem (1992), a one-way MANOVA
was constructed to test for differences in site characteristics (tree density, stem density,
canopy cover, and volume) and tree characteristics (height, canopy volume, stem size,
and number of stems) among the four sites, and 95% simultaneous confidence intervals
were constructed to determine which mean components differed among the four Prosopis
populations. Data were transformed prior to statistical analysis to correct for departures
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from normality and homogeneity of variances. Data were then back-transformed for
presentation. Phoradendron infection ratings were grouped into four classes (0 = no
infection; 1 and 2 = light; 3 and 4 = moderate; 5 and 6 = heavy). A chi-square test of
homogeneity was constructed according to Ott (1993) to test for proportional differences
in Phoradendron infection class and tree age class among the four sites.
Prosopis tree cross-sections were obtained from one or two relatively large single
stemmed trees at each site to determine approximate stand age. An effort was made to
obtain cross-sections from stumps of trees that had been recently cut. Cross-sections
were sent to a lab affiliated with the Laboratory of Tree-Ring Research at Tucson,
Arizona for aging, using the methods of Flinn et al. (1994).
Data on existing water wells in the general vicinity of each site were obtained
from the Nevada State Water Engineer’s Office in Las Vegas to determine if a trend in
groundwater fluctuations over time could be established. Information obtained from the
well logs included well location, the date the well was drilled, and the static water level
for that date. Elevation at each water well location was determined from 1:24000 scale
topographic maps, and a correlation matrix was constructed to determine and correct for
any influence of elevation on water level. Simple linear regression was used to determine
if a relationship between time and water level existed.
One monitoring well was drilled at each site to determine current water table
levels and to monitor long-term groundwater fluctuations. Drilling was conducted by the
Bureau of Reclamation, Yuma, Arizona using a CME-1250 hollow-stem auger drilling rig
with a 4-inch I D. hollow stem for installing casing and well screen. Two-inch PVC was
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used for the well casing. A surface seal consisting of neat cement with bentonite was
placed at each site, and a metal surface protective casing with locking cap was installed
over each monitoring well. The depth at which moist soil was detected was recorded to
determine the thickness of the capillary fringe. The initial depth to saturated soil was
recorded, and a second reading was taken a few days later. Soil samples were collected
from the mid-portion of each 1.5-m depth interval during drilling and sent to Utah State
University Analytical Labs in Logan, Utah for analysis. Soils were analyzed for mineral
content, texture, and pH, and surface samples were analyzed for nitrogen content.
Results and Discussion
Information on existing wells obtained from the Nevada State Water Engineer’s
Office indicated that groundwater at Stewart Valley was closer to the soil surface than at
the other three sites. Static water levels of previously drilled wells at Stewart Valley
ranged from less than 3 m prior to 1970 to almost 10 m for a well drilled in 1995 (Fig. 2-
2B). Water table level at Moapa was much less predictable (R^ = 0.09), with static water
levels of existing wells fluctuating between 5 m and 25 m in depth from 1970 to present
(Fig. 2-2A). Water table level at Pahrump was estimated to be approximately 15 m deep
(Fig. 2-2C). The large number of existing water wells within the general vicinity of
Pahrump is due to its close proximity to the community of Pahrump. Fig. 2-2C shows
that there has been a general decline in the water table level in this area over the past 50
years (R^ = 0.51). Wells drilled in the 1950's and 1960's were mainly for irrigation
purposes, but pumpage began to decrease after 1968 when land was taken out of
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■D CD
WC/) o"3 Moapa Stewart Valley O 3 0.0 CD 8 5 .0 ■O > 10.0 (O' i l o 1 5 .0
20.0 Q) 2 0 .0 II R* = 0.09 R" = 0.39 2 5 .0 3. 3" 3 0 .0 CD 1940 1950 1960 1970 1980 1990 2000 2000 ■DCD Year O Pahrum Q. C 0.0 Oa 3 5 .0 ■D 5 O ^ 10.0 I 3 CD 1 5 .0 Q. i _U û) 20.0 R^ = 0.51 6 2 5 .0 ■D CD 3 0 .0 (/) 1940 1950 I960 1970 1 9 8 0 1 9 9 0 2000 Year
Fig. 2-2. Linear regression of static water levels and year wells were drilled in the vicinity of three Prosopis woodland sites in southern Nevada.
w LA 3 6
agriculture and sub-divided for real estate (Harrill 1982). Currently, the area is closed to
any new irrigation wells, but the number of domestic wells has increased since the mid-
1980s. No information was available for Stump Spring except for the discovery of old
logsheets for a well located 2 km from the site. The water level was recorded at 46 m in
1959 and 51 m in 1976. From this information it was assumed that Stump Spring should
have the deepest water table level.
Appendix II lists the results from the soil analysis. Soils at all sites were alkaline,
with pH values ranging from 7.9 to 8.5. Phosphorus, potassium, and nitrogen levels were
variable, with Stewart Valley containing the lowest levels of all three for surface soils.
Nitrogen levels of surface soils were much higher at Moapa (20.2 mg kg ') and Pahrump
(20.8 mg kg ') than at Stewart Valley (2.2 mg kg ') and Stump Spring (8.0 mg kg '),
possibly due to the influence of fertilizers used for agricultural fields located close to
Moapa and Pahrump.
Results from the MANOVA indicated that a significant difference existed among
the four sites for both tree characteristics (Wilk’s lambda = 0.24; F = 6.25; df = 12, 106; p
< 0.0001) and site characteristics (Wilk’s lambda = 0.24; F = 6.42; df = 12, 106; p <
0.0001). Calculations of 95% simultaneous confidence intervals indicated that Stewart
Valley was the most structurally unique site. Of the four site characteristics calculated,
canopy volume at Stewart Valley was significantly greater than at Moapa and Pahrump
(Fig. 2-3C), and stem density at Stewart Valley was less than that at Moapa and Stump
Spring (Fig. 2-3D). Tree density was lowest and canopy cover highest at Stewart Valley,
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■a CD
C/) C/) Tree Density Canopy Cover
1 5 0 - ■D8
(O' -C 1 0 0 -
5 0 -
MO SV PA SS MO SV PA 88 3"3. CD Site B Site ■DCD O Q. C Canopy Volume Stem Density Oa 3 3 .5 "O 1000 - o 3 .0 -1 E 2 .5 (0 ab sz CD E 2.0 H ab Q. 5 0 0 - 0) 1 .5 E 3 1.0 - CO O > 0 . 5 - ■D 0.0 CD — 1— — 1— MO PA 88 MO SV PA 88 (/) (/) Site D Site
Fig. 2-3. Differences in site characteristics of four Prosopis woodlands in southern Nevada. Bars represent the mean value ± 1 SE. Characteristics for sites with the same letter are not significantly different (P > 0.05). MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring. 3 8
but these characteristics were not significantly different from the other three sites (Figs. 2-
3 A and 2-3B). No differences were detected in any of the four site characteristics among
Moapa, Pahrump, and Stump Spring sites. Of the four tree characteristics, Stewart Valley
contained the tallest trees (Fig. 2-4A) and the largest stems (Fig. 2-4D) of the four sites.
Canopy volume for trees at Stewart Valley was significantly greater than at Moapa and
Pahrump (Fig. 2-4B) and number of stems for Stewart Valley trees was less than for trees
at Stump Spring (Fig. 2-4C). As was found for site characteristics, no differences were
detected in the four tree characteristics among Moapa, Pahrump, and Stump Spring sites.
Prosopis age class distribution was significantly different among the four sites
(Fig. 2-5). All sites contained a large proportion of mature trees, which is not uncommon
for Prosopis growing in an arid climate (Mooney et al. 1977). However, Stewart Valley
and Pahrump contained a larger proportion of saplings than Moapa and Stump Spring.
Proportion of seedlings was highest at Stewart Valley, whereas seedling establishment
was not observed at Moapa and Stump Spring. Proportion of dead trees was highest at
Stump Spring. Overall, age class was more evenly distributed at Stewart Valley and
Pahrump than at Moapa and Stump Spring.
Intensity of Phoradendron infection was significantly different among the four
sites (Fig. 2-6). A larger percentage of trees were infected at Pahrump, with more than
30% being heavily infected. Infection intensity was more evenly distributed at Moapa,
whereas most infected trees at Stewart Valley were only lightly infected. Stump Spring
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■D CD
WC/) Tree Height Canopy Volume
9 0 0 8 3 0 - 6 0 0 - 20 - m E O) 5 o 3 0 0 10 - >
MO SV PA SS 3. 3" CD Site "OCD O Q.
3O Primary Stems Stem Diameter ■D O 1 0 - g 3 0 - 0) 0.05). MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring.
U) o CD ■ D O Q. C 8 Q.
"D CD
C/) C/) Mesquite Age Distribution
8 100% ■D 90% 80%
CD 70% 60% 3. 3" 50% CD C
CD 40% ■D g O Û. 0) 30% C Q_ aO 20% 3 ■D O 1 0 % 0% Q.CD MO SV PA 8 8 Site ■D CD M ature ■ Sapling Seedling ■ D ead
(/)
Fig.2-5. Age class distribution of Prosopis woodland study sites in southern Nevada. Distribution of age class among sites is significantly different = 184.341; df= 9; P < 0.0001). MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring.
ê CD ■ D O Q. C 8 Q.
■D CD
C/) C/) Mistletoe Infection
g "O 90% 80% g 70% CD S 60%
3. o 50% 3" CD c 40% ■DCD O 8 30% Q. C a S. 20% O 3 10% ■D O 0%
CD Q. MO SV PA SS Site
■D None a Light ^ Moderate H Heavy CD
c /) c /) Fig. 2-6. Proportional distribution of Phoradendron infection ratings by class (0 = none; 1 and 2 = light; 3 and 4 = moderate; 5 and 6 = heavy) at four Prosopis woodland sites in southern Nevada. Distribution of intensity class among sites is significantly different (X^ = 86.685; df= 9; P < 0.0001). MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring. 42
contained the smallest proportion ol infected trees, with 15% showing signs of light
infection.
Water table levels measured after installation of monitoring wells at each site are
shown in Fig. 2-7. As was predicted, the water table at Stump Spring was the deepest of
the four sites, at 24 m below the soil surface. Groundwater level at Pahrump was 18 m
deep, which was similar to the 15 m prediction from existing water level data (Fig. 2-2C).
However, groundwater level at Stewart Valley was 16 m deep, which was lower than
expected, and Moapa had the shallowest water table level at 12 m deep. But another
important factor that must be considered in determining groundwater availability to plants
is the depth and thickness of the capillary fringe, which is the zone of moist soil directly
above the aquifer. Fig. 2-7 shows that moist soil occurred 2.4 m below the soil surface at
Stewart Valley, whereas depth to the top of the capillary fringe at Moapa, Pahrump, and
Stump Spring was 7.6 m, 7.0 m, and 8.2 m, respectively. The capillary fringe is also
thicker at Stewart Valley, Pahmmp, and Stump Spring than at Moapa. It was determined
from the installation of monitoring wells and analysis of soil samples collected at each
site that Stewart Valley, Pahrump, and Stump Spring contain confined aquifers that are
under pressure due to a layer of dense, clay soils occurring above and below the aquifers
(Table 2-1). The greater thickness of the capillary fringe at Stewart Valley, Pahrump, and
Stump Spring is the result of water moving up through the soil away from the pressurized
aquifer. In contrast, the aquifer at Moapa is perched above a dense layer of clay soils
with a less dense upper layer of sandy soils. Hence, the groundwater at Moapa is not
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■D CD
C/) C/) Groundwater Levels
8 ■D 0.0 = 5.0 ^ ^ 10.0 CD 0 & 15.0 3. 3" ■û ü 20.0 CD ■DCD § *1 25.0 O Q. C 1 30 0 Oa 3 b 35.0 ■D â û û û û û û û â O 40.0
CD Q. MO SV PA SS Site
■D CD Dry Soil E3 Capillary Fringe Aquifer
C/) C/)
Fig. 2-7. Groundwater levels determined from the installation of monitoring wells at four Prosopis woodland sites in southern Nevada. MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring.
6 4 4
Table 2-1. Soil textures determined from soil samples obtained at 1.5-m intervals from water well drilling at four Prosopis woodland sites in southern Nevada. MO = Moapa; S V = Stewart Valley; PA = Pahrump; SS = Stump Spring.
Site
Depth (m) MOSVPASS
0 - 1.5 Sand SandyLoam SiltyClay Loam
1.5- 3.0 Sand Clay Clay Loam
3 .0 - 4.5 SandyClayLoa Clay Clay m
4 .5 - 6.0 Sand Clay Clay ClayLoam
6 .0 - 7.5 Sand Clay Clay ClayLoam
7.5- 9.0 Loamy Sand Clay Clay ClayLoam
9.0 - 10.5 Loamy Sand Clay ClayLoam
10.5 - 12.0 SandyClay ------Clay
12.0- 13.5 SiltyClay ClayLoam Clay SiltyClayLoam
13.5- 15.0 Clay ------Clay
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45
under as much pressure and does not tend to move up through the soil to the extent it
does at the other three sites with confined aquifers.
If distance to the capillary fringe is considered rather than distance to the aquifer,
a pattern emerges that is consistent with results from the vegetation analysis. Trees at
Stewart Valley were significantly larger than those at Moapa, Pahrump, and Stump
Spring, whereas no differences were detected in either site or tree characteristics among
the latter three sites. The capillary fringe occurs much closer to the soil surface at Stewart
Valley than at the other three sites, whereas depth to moist soil is similar at Moapa,
Pahrump, and Stump Spring. Others have found similar relationships between Prosopis
growth and water availability. Limited water availability can cause increasing water
stress in Prosopis that will eventually result in reduced plant growth (Haas and Dodd
1972). Hanson (1982) determined that net photosynthesis was significantly lower for
Prosopis subjected to higher water stress than for those occurring in areas with more
water availability. Nilsen et al. (1984) found that biomass and production for a Prosopis
woodland at Harper’s Well in southern California was greater in areas adjacent to a wash
where water was more available than at the outer edges of the stand. Stromberg et al.
( 1992) found that tree height and vegetation volume decreased with increasing depth to
groundwater, which is consistent with the results from this study with the exception of the
comparison of vegetation volume between Stewart Valley and Stump Spring (Fig. 2-3C).
The lack of a significant difference in vegetation volume between these two sites can be
explained by the relatively high canopy cover found at Stump Spring as compared to
Moapa and Pahrump (Fig. 2-3B). Trees at Stump Spring, Moapa, and Pahrump were
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shorter than trees at Stewart Valley, but canopy spread was greater at Stump Spring than
at Moapa and Pahrump, resulting in a greater volume estimate for Stump Spring.
This study found a consistent pattern between tree size and groundwater level;
however, other factors may contribute to differences in Prosopis tree growth form.
Physical damage to the main shoot or apical meristem promotes sprouting and transforms
tall single-stemmed trees into short, dense, multi-stemmed thickets (Mooney et al. 1977).
Fire, herbivory, trampling, freezing temperatures, wood-cutting, and chaining are
examples of physical or mechanical processes that can promote branching of Prosopis
trees (Heitschmidt et al. 1988, Mooney et al. 1977, Nilsen et al. 1987, Simpson and
Solbrig 1977). Evidence of fire damage was present, and most likely has contributed to
the branched growth form observed at all four sites. The effect of freezing temperatures
is less obvious. The Stump Spring, Pahrump, and Stewart Valley sites lie within
Pahrump Valley west of the Spring Mountains at elevations that range from 745 m to 865
m. The probability of freezing temperatures is greater in the Pahrump area than at
Moapa, which lies within Moapa Valley east of the Spring Mountains at an elevation of
470 m. If damage from freezing was a major factor in Prosopis growth form, Moapa
trees should show evidence of less branching than trees at Stump Spring, Pahrump, and
Stewart Valley, which was not the case. The extent and degree of wood-cutting,
trampling, and herbivory may be more plausible contributors to the differences in growth
form among the four sites. Prosopis trees at Moapa showed signs of both old and recent
wood-cutting. Moapa is easily accessible by road, and is located within an active grazing
allotment adjacent to irrigated agricultural fields.
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Potential increases in herbivory by rodents, lagomorphs, and livestock, and
trampling due to high levels of use, may also contribute to the prevalent branched growth
form at Moapa. The woodland at Pahrump does not lie within a grazing allotment, but
receives high levels of human use due to its easy access and proximity to the community
of Pahrump. Extensive wood-cutting has occurred at Pahrump, and may be a major
contributing factor to the branched growth form and reduced canopy cover found at this
site. The woodland at Stump Spring is less accessible, and shows little sign of recent
wood-cutting activity. However, trees at Stump Spring tend to be shorter, smaller, and
more branched than at any other site. Although grazing has not occurred recently, the site
had previously been exposed to intensive livestock grazing. In addition, the site may
have been exposed to high levels of human use in the mid to late 1800's due to its unique
history as a resting place along the Old Spanish Trail (Myhrer et al. 1990). The woodland
at Stewart Valley is also remote, but relatively undisturbed compared to the other three
sites. It does not occur as close to urban areas as Pahrump and Moapa and, unlike Moapa
and Stump Spring, does not have a past grazing history. Signs of recent wood-cutting
activity were observed, but old cuts were either absent or obscured by age. Tree ring
counts also indicate that undisturbed, single-stemmed trees at Stewart Valley are older
than those at the other three sites (Stewart Valley = 94 and 109; Moapa = 77 and 90;
Pahrump = 59 and 83; Stump Spring = 71).
Differences in Prosopis age class distribution among the four sites may be the
result of variations in physical and climatic conditions, as well as differences in
competition, herbivory, and fire frequency. Prosopis seedling establishment requires a
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precise occurrence of warm temperatures and precipitation, and consequently may be a
rare and episodic event in arid environments (Mooney et al. 1977, Wright et al. 1976).
Survival of seedlings under drought conditions also depends on how quickly roots can
reach available groundwater (Meinzer 1927). In addition, Prosopis seedlings have high
light requirements and do not readily germinate in dense vegetation or under its own
canopy (Bush and Van Auken 1987, Ueckert et al. 1979). Prosopis contains high
concentrations of nitrogen (West and Klemmedson 1978) and young, tender shoots
provide highly desirable forage for many herbivores (Nilsen et al. 1987, Rorabaugh 1995,
Wright and Bailey 1982). Young Prosopis are also susceptible to moderate fires and
burning may inhibit seedling establishment (Wright and Bailey 1982, Wright et al. 1976).
It is evident that any one or combination of the above factors may have influenced
differences in age class distribution among the four study sites. The relatively high
proportion of seedlings and saplings at Stewart Valley may be explained by the shallow
water table present at this site. Although the water table is lower at Pahrump than
Stewart Valley, increased availability of soil moisture due to runoff from the road
flanking the woodland may be partially responsible for the presence of seedlings and
saplings at Pahrump. In addition, livestock grazing has not occurred at either the Stewart
Valley or Pahrump sites. Herbivory pressure at Moapa may be high, as this site lies
within a grazing allotment. Rodent and lagomorph populations may also be high at this
site due to the presence of agricultural fields adjacent to the woodland, and may
contribute to the absence of seedlings observed at Moapa. The lack of available water
may be the factor most responsible for absence of seedling establishment at Stump
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Spring. Groundwater level at this site is lowest, and availability of surface water is
limited to infrequent runoff from intense rainstorms.
Differences in the intensity of Phoradendron infection among the four sites may
be the result of differences in temperature, light, and host water relations. Phoradendron
califomicum is sensitive to cold temperatures (Boyce 1961, Hollinger 1983, Wagener
1957). Net photosynthesis is dramatically reduced at temperatures below 20°C, and
freezing temperatures cause dieback of aerial shoots. The three sites located within
Pahrump Valley (Stewart Valley, Pahrump, and Stump Spring) are exposed to cooler
temperatures than Moapa, which is located in Moapa Valley at a lower elevation. Much
of the Phoradendron at Stewart Valley and Pahrump had died due to an extended period
of freezing temperatures in 1990, and Phoradendron berry production appeared to be less
at sites in Pahrump Valley than at the Moapa Valley site. However, Pahrump has the
greatest proportion of infected trees, as well as the greatest proportion of trees with heavy
infection. The high frequency of occurrence of Phoradendron at Pahrump may be the
result of the location of the Prosopis woodland, which is flanked to the north by a major
road. Norton et al. (1995) found that mistletoe was more abundant along road edges
where run-off from precipitation allowed for higher relative water content of the host
plant. A similar situation is present at Moapa, where relative intensity of infection is also
high, and run-off from adjacent irrigated agricultural fields may increase the availability
of water.
It is well documented that mistletoe exhibits regulation of transpiration and
stomatal conductance relative to that of its host (Davidson and Pate 1992, Davidson et al.
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1989, Ehlerihger et al. 1986, Glatzel 1983, Schulze et al. 1984, Ullman et al. 1985,
Whittington and Sinclair 1988); the regulation is determined by the hydraulic
conductivity and water content of the host tissue (Schulze and Ehleringer 1984). The
independent stomatal control systems of parasite and host in situations of abundant water
supply become more closely linked as water availability decreases (Glatzel 1983).
Control of transpiration under conditions of water stress avoids placing undue stress on
the host plant, thus ensuring the long-time survival of both parasite and host (Ullman et
al. 1985). Reid and Lange (1988) documented mistletoe death and loss of canopy volume
under conditions of drought, and suggested that water stress may at least be indirectly
responsible for reduction in mistletoe infection. Lack of available water and cooler
temperatures may explain the low frequency and intensity of infection at Stump Spring,
where distance to the water table is greatest, elevation is highest, and water from runoff
is present only during periods of intense rainfall events. However, the low infection at
Stewart Valley relative to Pahrump is not as readily explainable. Climatic conditions are
similar at both sites, and groundwater is closest to the soil surface at Stewart Valley, yet
Phoradendron infection is relatively light at Stewart Valley. Availability of light may
contribute to the extent of infection. Mistletoe is intolerant to shade and grows best in
places where it receives the greatest amount of light (Boyce 1961, Kuijt 1969, Leonard
and Hull 1965). Most large mistletoe plants are found on the upper crown of tall trees
growing in more open groves (Boyce 1961). Canopy cover and volume is greatest at
Stewart Valley, and Phoradendron growth at this site may be at least partially limited by
light availability.
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This study has demonstrated that Prosopis trees in southern Nevada can grow to
great size in areas where groundwater occurs close to the soil surface, and are smaller
with more stems in areas where depth to the capillary fringe is greater. Trees at Stewart
Valley reached heights as great as 8 m and contained stems nearly one m in diameter,
rivaling the size of trees found in more mesic environments such as the floodplains of
rivers (Meinzer 1927). The installation of permanent groundwater observation wells will
enable the long-term monitoring of groundwater level and assist in future studies of
Prosopis growth response to fluctuating water table levels in southern Nevada.
Identification of factors influencing Prosopis growth will assist in the preparation of a
Mesquite Woodland Habitat Management Plan for the Las Vegas Field Office of the
Bureau of Land Management. Long-term management of Prosopis woodlands on Public
Lands in southern Nevada will ensure the continued existence of one of the few native
tree species in Nevada that has adapted to the harsh, arid climate of the Mojave Desert.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 2
Literature Cited
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, __ , and . 1984. Productivity in native stands of Prosopis glandulosa, mesquite, in the Sonoran Desert of southern California and some management implications. Pages 722-727 in R. E. Warner and K. M. Hendrix (eds.). California Riparian Systems: Ecology, Conservation, and Productive Management. University of California Press, Berkeley and Los Angeles, CA.
, M. R. Sharifi, R. A. Virginia, and P. W. Rundel. 1987. Phenology of warm desert phreatophytes: seasonal growth and herbivory in Prosopis glandulosa var. torreyawa (honey mesquite). Journal of Arid Environments 13:217-229.
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Rundel, P. W., E. T. Nilsen, M. R. Sharifi, R. A. Virginia, W. M. Jarrell, D. H. Kohi, and G. B. Shearer. 1982. Seasonal dynamics of nitrogen cycling for a Prosopis woodland in the Sonoran Desert. Plant and Soil 67:343-353.
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, S. D. Wilkins, and J. A. Tress. 1993. Vegetation-hydrology models: implications for management of Prosopis velutina (velvet mesquite) riparian ecosystems. Ecological Applications 3:307-314.
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Ecosystems. US/IBP Synthesis Series 9, Dowden, Hutchinson & Ross, Inc., Stroudsburg, PA.
Whittington, J. and R. Sinclair. 1988. Water relations of the mistletoe, Amyema miquelii, and its host Eucalyptus fasciculosa. Australian Journal of Botany 36:239-255.
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Wright, H. A. and A. W. Bailey. 1982. Fire Ecology. John Wiley & Sons, New York, NY.
Wright, H. A., S. C. Bunting, and L. F. Neuenschwander. 1976. Effect of fire on honey mesquite. Journal of Range Management 29:467-471.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTERS
AVIAN USE OF FOUR Prosopis (HONEY MESQUITE)
WOODLANDS IN SOUTHERN NEVADA
Introduction
Prosopis (mesquite) woodlands provide important habitat for avian species in
desert environments. In the Mojave Desert of southern Nevada, the expanse of desert
scrub is only occasionally interrupted with patches of Prosopis that provide birds with
food, cover, and protection from the elements of a harsh arid climate. The occurrence of
Prosopis woodlands adds structural complexity to the environment, resulting in typically
higher bird densities than in the surrounding desert vegetation (Germano et al. 1983,
Laudenslayer 1981) Phoradendron califomicum (desert mistletoe) that parasitizes
Prosopis produces berries that many desert birds rely on for food (Cowles 1972, Overton
1993), and moisture from the berries can provide birds with enough water to survive in
areas devoid of other water sources (Crouch 1943, Hensley 1954, Walsberg 1975).
Prosopis habitat supports several species of desert breeding birds such as Vermivora
luciae (Lucy’s Warbler) and Phainopepla nitens (Phainopepla) that depend heavily on
Prosopis for food and nesting sites (Anderson and Ohmart 1978, Meents et al. 1983).
Patches of Prosopis scattered throughout the desert serve as oases for fat-depleted
58
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migratory birds attempting to cross this large ecological barrier (BerthoId and Terrill
1991), and provide important stopover sites where birds can rest and refuel for the
remainder of their journey to their breeding or wintering grounds (Kuenzi and Moore
1991, Rappole and Warner 1976, Terborgh 1992).
Southern Nevada supports several Prosopis woodlands containing large trees,
where the presence of shallow groundwater has allowed Prosopis to reach heights as
great as 8 m with stems as large as 86 cm in diameter. These woodland communities
have been largely overlooked in the past, but have recently become a concern due to
increasing urban populations and declining water table levels. Much of southern
Nevada’s Prosopis habitat lies within and adjacent to urban communities, where the
requirement of a permanent, reliable water source has placed Prosopis in direct
competition for scarce water supplies with a growing human population. Much of Las
Vegas Valley’s Prosopis woodlands has been lost due to urban growth, and the remaining
woodlands are threatened with increasing disturbance from human use, including
uncontrolled wood-cutting, declining water table levels, and increased herbivory,
trampling, and fire frequency. Prosopis growth and survival declines as distance to the
water table increases (Cannon 1913, Haas and Dodd 1972, Holland 1987, Judd et al.
1971, Minckley and Clark 1984, Robinson 1958, Stromberg et al. 1993) and extensive
damage to the main stem can change the structure of a woodland from large, single
stemmed trees to short, dense, multi-stemmed thickets (Fisher 1977, Heitschmidt et al.
1988).
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The objectives of this study were to document avian species composition and
community patterns within four of southern Nevada’s remaining Prosopis woodlands,
and to determine if differences in avian density, species richness, and species diversity
existed among the four sites. Results from the vegetation study in Chapter 2
demonstrated that Prosopis growing at the site with groundwater closer to the soil surface
were larger and taller than those found at sites with deeper water tables. It was the
purpose of this study to determine if these differences would also reflect differences in
avian community indices. The relationship between habitat structure and avian
community patterns has been well-studied (Hansen et al. 1995, James 1971, Mac Arthur
and MacArthur 1961, Rice et al. 1984, Robinson and Holmes 1984, Rotenberry 1985,
Rotenberry and Wiens 1980), and it is generally known that avian density, species
richness, and species diversity increase with increasing volume and complexity of the
habitat (MacArthur et al. 1962, MacArthur 1965, Mills et al. 1991). However, the use of
density and diversity indices has been criticized in the past (James and Rathbun 1981,
Mills et al. 1991, Van Home 1983), and many researchers have found cases where density
and diversity did not adequately describe avian response to its habitat (Baida 1969,
Tomoff 1974, Willson 1974). This study used all three indices in order to determine
which index or combination of indices would be the most useful in describing the avian
communities of Prosopis woodlands in southern Nevada.
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Materials and Methods
Avian surveys were conducted from February through June of 1996 and 1997
within the four Prosopis woodlands described in Chapter 2. Each site contained
relatively small, narrow, linear patches of Prosopis', therefore, complete counts were used
at each location. It was assumed that all birds were either seen or heard, and individual
sightings during each survey were not duplicated. The area surveyed within each site
was: Moapa = 12 ha; Stewart Valley = 7 ha; Pahrump = 9 ha; Stump Spring = 9 ha. All
sites were surveyed twice each month. Surveys began one-half hour after sunrise, and
counts were obtained by walking at a steady pace along a set route through the middle of
each woodland for the entire length. Starting points of surveys were alternately reversed.
Rainy or windy days were avoided to minimize bias in detectability among sites due to
climatic variation.
Data were recorded on species and number of individuals seen or heard. Species
were categorized as either winter, breeding, edge, migratory, or raptor. Winter species
were those observed primarily in February and March. Signs of breeding activity were
noted, such as territorial behavior, presence of nests or nest-building activity, inflamed
cloaca, or presence of young. Breeding species that used the woodland for perching or
foraging but not for nesting were noted as edge species. Raptors that were observed
breeding in Prosopis were categorized as breeding.
Avian abundance for each site was standardized to individuals per 7 ha to
facilitate comparisons among unequal-area sites. Monthly averages for each site were
used to calculate density, species richness, and species diversity for all species and for
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breeding species only. Species diversity was calculated using the Shannon-Weiner
diversity index as described in Magurran (1988):
H' = -[Z(pJnpJ]
where H' = Shannon’s Index and p; = the proportional abundance of the ith species.
Variables were log-transformed and a three-way ANOVA using site, month, and year as
fixed-effects was used for each variable to test for differences in the three factors, as well
as site x month and site x year interactions. Separate tests were conducted for all species
combined and for breeding species only. Tukey’s multiple-comparison procedure was
used to determine which sample means were significantly different (Ott 1993). Data were
back-transformed for presentation. Results were compared with those obtained from the
vegetation analysis in Chapter 2 to determine if a relationship could be detected between
differences in Prosopis canopy cover and volume and avian community indices among
the four sites.
Results and Discussion
A total of 65 bird species were observed within the four study sites for both years,
which consisted of 30 breeding species, 21 migratory passerines, 6 wintering species, and
3 edge species (see Appendix HI). The three edge species (Brewer’s Sparrow, Greater
Roadrunner, and Say’s Phoebe) used the woodlands as perching and foraging sites, but
were not observed breeding within the woodlands. Eight raptor species were observed, of
which 3 were known to be breeding within the woodlands (Great Homed Owl, Long
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eared Owl, and Sharp-shinned Hawk). Nocturnal raptors were most likely
underestimated, as surveys were conducted during the day. However, one nocturnal
survey was conducted in 1996 at all four sites using owl-call tapes, and confirmed the
presence of Long-eared Owls at Stewart Valley.
Results of the three-way ANOVA for all species indicated that avian density,
species richness, and species diversity were similar between years for all sites combined,
and among sites when month and year were considered (Table 3-1). Differences among
months for all three variables were significant, which was expected due to the influx of
migrating species in May. There were overall site differences in avian density and
species richness, but species diversity was similar for all four sites. Avian density at
Moapa was significantly greater than at Pahrump, and species richness at Moapa was
greater than at all other sites (Fig. 3-1). No differences were detected for the three
variables among the Pahrump, Stump Spring, and Stewart Valley sites.
Results for breeding birds were similar to those for all species combined. No
differences were detected for any of the three variables between years or among sites
when month and year were considered (Table 3-2). Month to month differences existed
for all three variables, due to the arrival of migrating breeding birds and increasing
numbers of fledged young in May. Overall species richness was significantly different
among sites, but, unlike results from all species combined, no significant differences in
breeding bird density were found among the four sites. Species richness at Moapa was
significantly greater than that at Stewart Valley or Stump Spring, but did not differ from
Pahrump (Fig. 3-2). As was found for all species combined, species diversity for
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Table 3-1. Results of three-way ANOVA rncluding site by month and site by year interactions for all bird species surveyed from February through June of 1996 and 1997
Variable Source df F P Density site 3 5.21 0.011 month 4 23.45 <0.001 year 1 0.1 0.934 site X month 12 1.74 0.149 site X year 3 0.69 0.573
Species richness site 3 6.49 0.004 month 4 22.96 <0.001 year 1 0.10 0.760 site X month 12 1.04 0.465 site X year 3 1.31 0.304
Species diversity site 3 0.66 0.591 month 4 13.02 <0.001 year 1 0.11 0.743 site X month 12 0.90 0.563 site X year 3 0.20 0.893
Table 3-2. Results of three-way ANOVA including site by month and site by year interactions for breeding bird species surveyed from March through June of 1996 and 1997 within four Prosopis woodland sites in southern Nevada. Variable Source df FP Density site 3 1.95 0.176 month 3 14.79 <0.001 year 1 0.79 0.391 site X month 9 0.85 0.587 site X year 3 0.32 0.810
Species richness site 3 5.14 0.016 month 3 18.03 <0.001 year 1 0.67 0.430 site X month 9 0.75 0.660 site X year 3 1.15 0.370
Species diversity site 3 1.26 0.332 month 3 34.87 <0.001 year 1 1.65 0.223 site X month 9 0.93 0.534 site X year 3 3.41 0.053
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ■o I I
%
(gC/) o' 3 Density Species Richness
8 ro 50 c5'
3 CD
C p.
CD ■o Species Diversity CI a 2.4 - o 3 ■o o 2.0 -
&
co MO SV PA S3 Site %
C/)(g o' 3 Fig. 3-1. Comparison of avian community indices for all bird species surveyed within four Prosopis woodland sites in southern Nevada. Data from 1996 and 1997 were combined. Tukey’s multiple-comparison procedure was used to perform mean separation tests. Indices for sites with the same letter are not significantly different (P > 0.05). Interval bars represent 1 SE from the mean. MO = Moapa; SV = Stewart Valley; PA = Pahrump; SS = Stump Spring.
LAON CD ■ D O Q. C 8 Q.
■D CD
C/) C/) Density Species Richness
8 m ■D x :
(O'
o Z
SV PA 3. Site 3" CD ■DCD O CQ. Species Diversity Oa 3 ■D O
CD Q.
■D CD
C/) C/) Fig. 3-2. Comparison of avian community indices for breeding birds surveyed within four Prosopis woodland sites in southern Nevada. Data from 1996 and 1997 were combined. Tukey’s multiple-comparison procedure was used to perform mean separation tests. Indices for sites with the same letter are not significantly different (P > 0.05). Interval bars represent 1 SE from the mean. See Fig. 3-1 for explanation of site abbreviations.
o\ ON 6 7
breeding birds was similar for all four sites, and no differences were detected for all three
variables among the Pahrump, Stump Spring, and Stewart Valley sites.
Comparisons of monthly averages of the three avian indices among the four sites
for each year are shown in Fig. 3-3 for all bird species combined and in Fig. 3-4 for
breeding species only. Densities of all species at Moapa were greatest in February,
March, and April for both years, but Stewart Valley supported greater densities in May
and June for both years (Fig. 3-3). Species richness at Moapa was consistently the
highest of the four sites for all months in both years except in June of 1996, when Stewart
Valley had the greatest species richness (Fig. 3-3). Species diversity was consistently
similar among the four sites for all months in both years (Fig. 3-3). A similar pattern was
observed for breeding bird species (Fig. 3-4). Breeding bird densities in 1996 were
highest for Moapa in April, but Stewart Valley supported the greatest densities in May
and June. In 1997 breeding bird densities at Moapa remained fairly constant from March
through June and were similar to densities at Pahrump and Stump Spring in May and
June, whereas Stewart Valley again contained the highest densities of breeding birds in
May and June of 1997. Species richness for breeding bird species remained highest at
Moapa except for the months of June 1996 and April 1997. As was found for all species
combined, diversity of breeding bird species was consistently similar among the four sites
for all months in both years.
Results from the Prosopis woodland vegetation analysis described in Chapter 2
indicated that vegetation volume at Stewart Valley was significantly greater than that at
Moapa (Stewart Valley = 2.96 m^ m'^; Moapa = 1.47 m^ m'^; P < 0.05). Prosopis in
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. "OCD O Q. C g Q.
■D CD
C/) C/)
1 9 9 6 1 9 9 7 MO 140 2 120 -.-MO 120 -m- S V 100 100 - * .P A 8 & 80 -S s I 80 -■ -S S ■D 2 60 i 60 40 40 (O' I 20 20 Ô a 0 Feb Mar Apr M a y J u n Feb M a r A pr M a y Jun M o n th Month
1 9 9 6 1 9 9 7 35 35 3"3. 30 CD 25 I : 20 CD I V — • ■D 1 5 I : O 1 0 - 10 Q. C 5 I a 0 O Fob Mar Apr y J u nMa Feb M a r Apr M a y 3 Jun "O M o n th M onth o 1 99 6 1 9 9 7 5 5 CD Q. 0 0 5 Ü 2. 5 f 0 0 5 5 -M O I 0 0 ■D 0) - SV CD 5 • PA 5 -SS I 0 I 0 ill (/) Feb M arApr M ay Jun (/) Feb M ar Apr May Jun M onlh M onth
Fig. 3-3. 1996 and 1997 monthly averages of avian community indices for all bird species observed in four Prosopis woodlands in southern Nevada. See Fig. 3-1 for explanation of site abbreviations.
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m. Oto ob P Z «C
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 0
southern Nevada begins green-up in early to mid April and is fully leafed out by early
May. Greater densities of birds at Stewart Valley in May and June coincide with higher
foliage volumes at this site, whereas greater densities of birds at Moapa in February,
March, and April prior to Prosopis budbreak are related to factors other than foliage
volume.
Examination of month to month trends for the four sites aids in the explanation of
differences in avian density and species richness between Moapa and the other sites.
When the entire period of February through June is considered, Moapa supported higher
avian densities and species richness in more months than the other three sites. Hence,
there were differences in density between Moapa and Pahrump, and species richness
between Moapa and the other three sites. However, higher densities and species richness
at Moapa cannot be explained by greater canopy cover or volume. The presence of
irrigated agricultural fields adjacent to Moapa has most likely contributed to higher avian
density and species richness in February, March, and April. Agricultural fields increase
the availability of water and insects, which in turn attracts more birds to adjacent
woodland habitats (Carothers et al. 1974, Mac Arthur 1964). High production of
Phoradendron berries at Moapa may also contribute to larger avian populations. Berry
production begins in the fall and peaks during winter and early spring (Overton 1993),
providing a reliable food source for avian species in desert environments during this time
of year (Cowles 1936, 1972, Tinnin et al. 1971). Phoradendron infection was high at
both Moapa and Pahrump, but a prolonged freezing period in 1990 killed much of the
Phoradendron at Pahrump, resulting in reduced berry production. It was observed during
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the course of avian surveys that Phoradendron berries were more abundant and persistent
at Moapa for both years than at any other site.
Results of this study indicated that the use of Shannon’s diversity index for
comparison of avian communities among the four Prosopis woodland habitats was not
particularly effective. Habitat patchiness and vertical complexity are two factors involved
in determining species diversity (MacArthur et al. 1962). The similarity of species
diversity indices may be a reflection of the similarity of these two factors among the four
sites, which is not surprising as all four study sites contained monospecific stands of
Prosopis with a tree-like growth form.
Higher densities for all species and for breeding species at Stewart Valley in May
and June reflect the effect of canopy volume on avian densities after Prosopis has fully
leafed out. In turn, higher canopy volume at Stewart Valley reflects the occurrence of a
shallow groundwater level at this site. However, this study was not designed to test for
differences in avian community indices within each month, and small sample sizes
prohibited monthly statistical comparisons. Future studies should concentrate on more
intensive sampling after Prosopis has fully leafed out to test the hypothesis that greater
canopy volume in areas with shallow water tables supports greater densities of birds.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 2
Literature Cited
Anderson, B. W. and R. D. Ohmart. 1978. Phainopepla utilization of honey mesquite forests in the Colorado River Valley. Condor 80:334-338.
Baida, R. P. 1969. Foliage use by birds of the oak-juniper woodland and ponderosa pine forest in southeastern Arizona. Condor 71:399-412.
Berthold, P. and S. B. Terrill. 1991. Recent advances in studies of bird migration. Annu. Rev. Ecol. Syst. 22:357-378.
Cannon, W. A. 1913. Some relations between root characters, ground water and species distribution. Science 37:420-423.
Carothers, S. W., R. R. Johnson, and S. W. Aitchison. 1974. Population structure and social organization of southwestern riparian birds. American Zoologist 14:97- 108.
Cowles, R. B. 1936. The relation of birds to seed dispersal of the desert mistletoe. Madrono 3:352-356.
. 1972. Mesquite and mistletoe. Pacific Discovery 25(3): 19-24.
Crouch, J. E. 1943. Distribution and habitat relationships of the phainopepla. Auk 60:319-333.
Fisher, C. E. 1977. Mesquite and modem man in southwestern North America. Pages 177-188 in B. B. Simpson (ed.). Mesquite: Its Biology in Two Desert Scrub Ecosystems. US/IBP Synthesis Series 4, Dowden, Huthinson & Ross, Inc., Stroudsburg, PA.
Germano, D. J., R. Hungerford, and S. C. Martin. 1983. Responses of selected wildlife species to the removal of mesquite from desert grassland. Journal of Range Management 36:309-311.
Haas, R. H. and J. D. Dodd. 1972. Water-stress patterns in honey mesquite. Ecology 53:674-680.
Hansen, A. J., W. C. McComb, R. Vega, M. G. Raphail, and M. Hunter. 1995. Bird habitat relationships in natural and managed forests in the west Cascades of Oregon. Ecological Applications 5:555-569.
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Heitschmidt, R. K., R. J. Ansley, S. L. Dowhower, P. W. Jacoby, and D. L. Price. 1988. Some observations from the excavation of mesquite root systems. Journal of Range Management 41:227-231.
Hensley, M. M. 1954. Ecological relations of the breeding bird population of the desert biome in Arizona. Ecological Monographs 24:185-207.
Holland, D. C. 1987. Prosopis (Mimosaceae) in the San Joaquin Valley, California: vanishing relict or recent invader? Madrono 34:324-333.
James, F. C. 1971. Ordinations of habitat relationships among breeding birds. Wilson Bull. 83:215-236.
and S. Rathbun. 1981. Rarefaction, relative abundance, and diversity of avian communities. Auk 98:785-800.
Judd, B. I., J. M. Laughlin, H. R. Guenther, and R. Handegarde. 1971. The lethal decline of mesquite on the Casa Grande National Monument. Great Basin Naturalist 31:153-159.
Kuenzi, A. J. and F. R. Moore. 1991. Stopover of neotropical landbird migrants on East Ship Island following trans-Gulf migration. Condor 93:869-883.
Laudenslayer, W. F. 1981. Habitat utilization by birds of three desert riparian communities. PhD dissertation, Arizona State University. 148 pp.
MacArthur, R. H. 1964. Environmental factors affecting bird species diversity. American Naturalist 98:387-397.
. 1965. Patterns of species diversity. Biological Review 40:510-533.
and J. W. MacArthur. 1961. On bird species diversity. Ecology 42:594-598.
, __ , and J. Preer. 1962. On bird species diversity: O. Prediction of bird census from habitat measurements. American Naturalist 96:167-174.
Magurran, A. E. 1988. Ecological Diversity and Its Measurement. Princeton University Press, Princeton, NJ. 179 pp.
Meents, J. K., J. Rice, B. W. Anderson, and R. D. Ohmart. 1983. Nonlinear relationships between birds and vegetation. Ecology 64:1022-1027.
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Minckley, W. L. and T. O. Clark. 1984. Formation and destruction of a Gila River mesquite bosque community. Desert Plants 6:23-30.
Mills, G. S., J. B. Dunning, Jr., and H. M. Bates. 1991. The relationship between breeding bird density and vegetation volume. Wilson Bull. 103:468-479.
Ott, R. L. 1993. An Introduction to Statistical Methods and Data Analysis, 4th ed. Duxbury Press, Belmont, CA.
Overton, J. M. 1993. Dispersal in Mistletoes and Models. PhD dissertation, University of California, Los Angeles. 270 pp.
Rappole, J. H. and D. W. Warner. 1976. Relationship between behavior, physiology, and weather in avian transients at a migratory stopover site. Oecologia 26:193-212.
Rice, J., B. W. Anderson, and R. D. Ohmart. 1984. Comparison of the importance of different habitat attributes to avian community organization. Journal of Wildlife Management 48:895-911.
Robinson, S. K. and R. T. Holmes. 1984. Effects of plant species and foliage structure on the foraging behavior of forest birds. Auk 101:672-684.
Robinson, T. W. 1958. Phreatophytes. Geological Survey Water-Supply Paper 1423, U.S. Government Printing Office, Washington, D C. 84 pp.
Rotenberry, J. T. 1985. The role of habitat in avian community composition: physiognomy or floristics? Oecologia 67:213-217.
and J. A. Wiens. 1980. Habitat structure, patchiness, and avian communities in North American steppe vegetation: a multivariate analysis. Ecology 61:1228- 1250.
Stromberg, J. C., S. D. Wilkins, and J. A. Tress. 1993. Vegetation-hydrology models: implications for management of Prosopis velutina (velvet mesquite) riparian ecosystems. Ecological Applications 3:307-314.
Terborgh, J. 1992. Perspectives on the conservation of Neotropical migrant landbirds. Pages 7-12 in J. M. Hagan HI and D. W. Johnston (eds.). Ecology and Conservation of Neotropical Migrant Landbirds. Smithsonian Institution Press, Washington, D C.
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Tinnin, R. O., C. L. Calvin, R. L. Null, and R. B. Cowles. 1971. Observations on the establishment of seedlings of Phoradendron califomiciim on Prosopis juliflora. Phytomorphology 21:313-320.
Tomoff, C. S. 1974. Avian species diversity in desert scrub. Ecology 55:396-403.
Van Home, B. 1983. Density as a misleading indicator of habitat quality. Journal of Wildlife Management 47:893-901.
Walsberg, G. E. 1975. Digestive adaptations of Phainopepla nitens associated with the eating of mistletoe berries. Condor 77:169-174.
Willson, M. F. 1974. Avian community organization and habitat structure. Ecology 55:1017-1029.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4
BREEDING SUCCESS AND NEST SITE SELECTION OF
Phainopepla nitens IN A SOUTHERN NEVADA
Prosopis WOODLAND
Introduction
Prosopis (honey mesquite) woodlands in southern Nevada provide important
habitat for Phainopepla nitens (Phainopepla), a glossy black songbird found only in the
southwestern United States and Mexico (American Ornithologists’ Union 1983). The
distribution of Phainopepla coincides with that of Prosopis, as its favorite food is the
berries of Phoradendron califomicum (desert mistletoe) that parasitizes Prosopis (Rand
and Rand 1943). Southern Nevada contains the northern periphery of Phainopepla's
range (Walsberg 1977), as well as that of Prosopis (Simpson and Solbrig 1977). It is
often assumed that peripheral populations are sinks that occur in marginal habitat, and are
not particularly important in the survival of the species as a whole (see Lomolino and
Channell 1995). Few studies have focused on Phainopepla because of its status as a
peripheral population in Nevada and its abundance in other parts of its range (Jones 1990,
unpubl. report). However, habitat specialists such as Phainopepla may be particularly
sensitive to changes in habitat quantity or quality (Meents et al. 1984). Degradation or
76
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loss of Prosopis habitat in southern Nevada may adversely affect Phainopepla
populations, resulting in a reduction of its existing range. In addition, recent studies have
reevaluated the assumption that peripheral populations are irrelevant, and have
emphasized the importance of peripheral sites as centers of genetic divergence and
spéciation (Davidson et al. 1996, Furlow and Armijo-Prewitt 1995, Lesica and Allendorf
1995, Lomolino and Channell 1995).
Concern for Phainopepla populations in southern Nevada developed after it
became evident that much of the area’s Prosopis woodlands had been lost to urban
growth. The arid desert climate of southem Nevada has restricted the distribution of
Prosopis to areas where groundwater is relatively close to the soil surface (Meinzer
1927, Nilsen et al. 1981). The requirement of a permanent, reliable water source has
placed southem Nevada Prosopis populations in direct competition for scarce water
supplies with a growing human population that is also dependent on the availability of
groundwater. An expanding human population also contributes to increased disturbance
of Prosopis woodlands, including uncontrolled wood-cutting, fire, herbivory, and
trampling. Stress and disturbance transforms large Prosopis trees into short, dense
thickets (Fisher 1977), which may in tum significantly alter its effectiveness as wildlife
habitat.
The objectives of this study were to locate breeding populations of Phainopepla
within four Prosopis woodlands in southem Nevada and to determine breeding season,
nesting success, and habitat requirements. Phainopepla's dependence on Phoradendron
is well documented (Anderson and Ohmart 1978, Crouch 1943, Laudenslayer 1981, Rand
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and Rand 1943, Snow and Snow 1988, Walsberg 1975), but little is known about the
structural component of its habitat in southem Nevada. A study on nest site selection was
conducted to determine if breeding Phainopepla preferred certain Prosopis stmctural
characteristics for nesting sites. Differences in structural characteristics were then related
to Phainopepla breeding success.
Materials and Methods
Breeding Season and Nesting Success
The four Prosopis woodlands described in Chapter 2 were searched for breeding
Phainopepla between February and June of 1996 and 1997. Moapa was the only site that
supported a breeding population, with the exception of one successful nest discovered at
Stump Spring in 1997. Nest searches at Moapa began on 5 April 1996 and 19 March
1997. Searches were conducted every three to four days within a 12-ha portion of the
Moapa woodland, and continued until the population vacated the area in May. Located
nests were monitored every three to four days, and data collected for each nest included
date, number of eggs, number hatched, and number of chicks fledged. Additional
information collected for nests included height of the nest and whether or not the nest was
built in a clump of Phoradendron. Locations of all nests were recorded with the use of a
Trimble® Pathfinder Pro XL GPS unit.
Nesting success was calculated using the methods of Mayfield (1961, 1975). The
nesting period was divided into two intervals: incubation period and nestling period.
Typical Phainopepla incubation period is 14 days and nestling period is 20 days
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79
(Walsberg 1977). Nest exposure was calculated by adding the number of nests found and
the number of days each nest was under observation (nest exposure days). Daily survival
rate (DSR) for each interval was calculated by dividing the total number of nest failures
(nests destroyed or abandoned) by the total number of nest exposure days and subtracting
from one. Interval survival rate (ISR) was calculated by raising DSR to the power of the
number of days in the interval. It was assumed that mortality rate was constant within an
interval. Egg hatching rate (EHR) was calculated by dividing the number of eggs that
hatched by the number of eggs present at hatching time. Nesting success (NS), defined as
the survival of any contents of the nest, was calculated by multiplying incubation ISR,
nestling ISR, and EHR to determine the probability that an egg at the start of incubation
will produce fledged young. Partial loss of nests was rare, and it was usual for either all
or none of eggs or young to survive. Therefore, individual egg mortality was negligible
and was not figured into total nesting success. Nesting success was calculated separately
for 1996 and 1997. Graphs of the nesting period were produced to determine peak
incubation, nestling, and fledging period for each year.
Nest Site Selection
A 0.04-ha circular plot ( 11.3-m radius) was placed around each nest tree, using
the nest tree as the center of the plot. All trees within each plot were measured for
height, canopy spread, canopy volume, number of primary stems, primary stem diameter,
and intensity of Phoradendron infection according to the methods described in Chapter 2.
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Twenty-six trees were randomly selected from the 185 trees sampled at Moapa for
the vegetation study in Chapter 2. Unpaired t-tests were used to compare tree height,
canopy volume, number of primary stems, and average stem diameter between randomly
selected trees and the 26 nest trees. T-tests were also used to test for differences in site
characteristics (tree density, percent canopy cover, canopy volume, and stem density)
between the 26 nest sites and the 15 vegetation plots sampled at Moapa. All variables
were transformed prior to statistical analysis to correct for departures from normality and
homoscedasticity. Variables were back-transformed for presentation.
Difference in intensity of Phoradendron infection between nest trees and random
trees was tested using a chi-square test of homogeneity as described in Ott (1993).
Infection intensity ratings for each tree range from 0 (no infection) to 6 (heavy infection).
Trees were placed into one of three classes according to their infection rating: 0 = class 1
(no infection); 1 and 2 = class 2 (light infection); 3, 4, 5, and 6 = class 3 (moderate to
heavy infection). Trees were placed into classes to ensure that no more than 20% of the
expected cell counts would be less than 5.
Pearson correlation coefficients were calculated and a correlation matrix was
constructed for the five tree variables tested (tree height, canopy volume, stems per tree,
stem diameter, and intensity of Phoradendron infection) for both nest trees and random
trees. Linear regression analysis was used to compare the relationship between tree
height and number of stems per tree for nest trees and random trees. Log-transformed
data were used for the analysis and the original data were used for presentation purposes.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81
The 185 trees sampled at Moapa for the vegetation study and the 26 nest trees
were placed into one of four categories according to their height and number of stems to
determine if Phainopepla was nesting in trees with specific structural components more
often than was available at the site. All 185 trees sampled at Moapa were used to obtain
an accurate estimate of habitat availability for the entire site. The four structural
categories were established as follows: 1) short trees with few stems; 2) short trees with
many stems; 3) tall trees with few stems; 4) tall trees with many stems. Short trees were
defined as trees < 4 m in height and tall trees were those > 4 m in height. Trees with few
stems were defined as those with < 6 primary stems and trees with many stems were those
with > 6 primary stems. A chi-square test of homogeneity was used to test for differences
in the distribution of tree structural category between nest trees (habitat use) and random
trees (habitat availability), and Bonferroni 90% simultaneous confidence intervals were
calculated for each of the four comparisons to determine if Phainopepla nested in trees
within each category in proportion to its availability (Marcum and Loftsgaarden 1980).
Results and Discussion
Breeding Season and Nesting Success
Phainopepla arrives on its breeding grounds at Moapa in late October-early
November. It occurs in flocks until the beginning of the breeding season in February or
March, at which time territories are formed and nest-building begins. The breeding
season typically lasts until the end of April or beginning of May, at which time the entire
population vacates the area. The results of avian surveys conducted at Moapa in 1996
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and 1997 indicated that Phainopepla began dispersing from the area between 7 May and
21 May in 1996 and between 24 April and 8 May in 1997. One female remained in the
area in 1996, and three females and one male were still present on 19 June in 1997.
Twenty-six nests were located; 10 nests in 1996 and 16 nests in 1997. Nests were
first discovered on 5 April in 1996 and 19 March in 1997. All nests that were discovered
contained either two eggs or two young, with the exception of one late nest found on 28
April 1997 that contained three eggs. In 1996, all eggs had hatched by 19 April (Fig. 4-
1). Chicks began fledging by 26 April 1996, and all young had fledged by 13 May 1996.
Two nests failed, and one of two eggs failed to hatch from a third nest (see Appendix Tv').
In 1997 ten nests had been discovered by 20 March, seven with eggs and three with
hatchlings (Fig. 4-2). The first fledglings appeared on 27 March 1997 and all young had
fledged by 2 May 1997. Three late nests with eggs were found between 21 April and 28
April, and all three eventually failed. Of the 13 nests that produced young in 1997 only
one egg failed to hatch.
Survival probabilities for each year are shown in Table 4-1. Survival rates during
the incubation period were lower than for the nestling period for both years, which is due
both to the failure of eggs to hatch in nests that produced at least one young, and to the
large number of nests found with young already hatched. Nesting success was higher in
1997 than in 1996 because of the greater number of nests found in 1997. Nest searching
effort was the same for both years, and it was assumed that the greater number of nests
discovered in 1997 was a reflection of an increase in the Phainopepla breeding
population at Moapa during this year.
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Phainopepla Breeding Season 1996
• Nests With eggs Nests w ith young Nests fledged
Date
Fig. 4-1. Number of nests under observation within each nesting stage during the 1996 Phainopepla breeding season at Moapa, Clark County, Nevada. Graph represents duration and peak period of each nesting stage.
Phainopepla Breeding Season 1997
• . Nests with eggs I i I liJ U M L — ■ — Nests with young I n 11 i 11 i I — A - N ests Hedged
I 1 I ; i c i I I I I O2 s E 4 3 Z 111 ; ' I i\i:L ' ' rkj. II II 1 Î •Q L I I M M ! i I y y / / y y y y Date
Fig. 4-2. Number of nests under observation within each nesting stage during the 1997 Phainopepla breeding season at Moapa, Clark County, Nevada. Graph represents duration and peak period of each nesting stage.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 4
Table 4-1. Nest survival probabilities ofPhainopepla nitens for 1996 and 1997 at
Incubation interval Nestling interval Year n' DSR" ISR' DSR ISREHR" NS' 1996 10 0.960 0.565 0.992 0.861 0.857 0.413 1997 16 0.968 0.639 0.994 0.895 0.937 0.537 n = number of nests ^ DSR = daily survival rate ISR = interval survival rate EHR = egg hatching rate ' NS = nesting success
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Average nest height was 2.6 m and ranged from 1.0 m to 5.1 m. Of the 26 nests
observed, 11 were built within a Phoradendron clump at a height > 3 m. All 15 nests that
were not built within a Phoradendron clump occurred at a height of < 3 m from the
ground. All five nests that failed in 1996 and 1997 were not built within a Phoradendron
clump and occurred at a height of < 3 m (see Appendix IV).
Nest Site Selection
Results of the t-tests for site characteristics indicated that there were no significant
differences in tree density, canopy cover, canopy volume, or stem density between nest
sites and random sites (Table 4-2). However, significant differences existed between nest
trees and random trees (Table 4-3). Nest trees were taller with larger canopy volumes and
stem diameters, but average number of stems per tree was similar for nest trees and
random trees. Proportion of nest trees with moderate to heavy Phoradendron infection
was greater than for random trees, while proportion of nest trees with no Phoradendron
infection was less than for random trees (Fig. 4-3).
Differences between nest trees and random trees for the four variables (tree
height, volume, stem diameter, and Phoradendron infection) are related to their
correlation with one another (Table 4-4). Trees with heavy Phoradendron infection
tended to be larger, taller trees, both for nest trees and random trees. All five variables
tested were either weakly correlated or strongly correlated for both nest trees and random
trees, with the exception of the comparison between tree height and number of stems per
tree. A somewhat strong negative correlation was found between tree height and number
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86
Table 4-2. Two-sample t-tests comparing Phainopepla nest site characteristics with
Nest site Woodland Variable n T SE“ n "x SE P Tree density" 26 131 15 15 142 15 0.50 % canopy cover 26 51.2 4.6 15 51.4 4.1 0.94 Volume' 26 1.63 0.17 15 1.47 0.12 0.78 Stem density" 26 727 126 15 773 90 0.44
" trees per ha. ' m’ per m‘. " stems per ha.
Table 4-3. Two-sample t-tests comparing Phainopepla nest tree characteristics with
Nest tree Random tree Variable n ~x SE n T SEP Tree height' 26 4.8 0.2 26 3.7 0.2 0.0009 Canopy volume" 26 166 22 26 94 14 0.016 Stems' 26 5.6 1.2 26 5.7 0.6 0.29 Stem diameter" 26 23.9 2.6 26 14.5 1.3 0.0037 m. " m'. ' number of stems per tree. " cm.
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Mistletoe Infection Classes
Nest tree CO % H Rarxjom tree
(U x t E 3
Fig. 4-3. Proportional differences in Phoradendron infection class between Phainopepla nest trees and random trees at Moapa, Clark County, Nevada. Distribution of infection class is significantly different at a = 0.05 (x^ = 7.785; df = 2; P = 0.02). Class 1 = no infection; class 2 = light infection; class 3 = moderate to heavy infection.
Table 4-4. Pearson correlation coefScients for tree structural characteristics of
Variable Height Volume Stems Stem diameter NT RTNT RTNT RTNTRT Volume 0.734 0.870 Stems -0.449 -0.112 -0.142 0.085 Stem diameter 0.758 0.716 0.663 0.657 -0.560 -0.329 MT ratine' 0.755 0.728 0.830 0.857 -0.355 -0.111 0.610 0.608
RT = random tree. ‘ MT rating = mistletoe infection rating.
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of stems per tree for nest trees, but was only weakly correlated for random trees (Table
4-4). Results of the linear regression analysis determined that a relationship existed
between tree height and stems per tree for Phainopepla nest trees, but not for random
trees, and that taller nest trees tended to have fewer stems than shorter nest trees (Fig.
4-4).
The homogeneity test determined that a significant difference in distribution of
trees among the four structural categories existed between nest trees and random trees
(Table 4-5). Construction of Bonferroni 90% simultaneous confidence intervals
determined that Phainopepla nested in short trees with few stems less often than what
was available, and used tall trees with few stems as nest sites more often than what was
available (Table 4-6). Phainopepla nested in short trees with many stems and tall trees
with many stems in proportion to their availability at Moapa. Overall, average number of
stems for nest trees and random trees was similar (Table 4-3), but once tree height was
considered it was evident that taller trees with fewer stems were preferred nesting sites.
Ten of the 15 nest trees that fell within the preferred structural category contained
moderate to heavy Phoradendron infection, while three were lightly infected and two
showed no signs of infection.
The strong correlation among the four significantly different variables prohibits
the determination of any single factor that may influence Phainopepla's choice of nest
trees (Martin 1989). It is most probable that intensity of Phoradendron infection is a key
determinant because of Phainopepla's strong reliance on Phoradendron berries for food
(Anderson and Ohmart 1978, Crouch 1943, Hensley 1954, Walsberg 1975).
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Nest Trees
3 0
2 3 4 5 6 7 8 Tree height (m) Random Trees 30 25 20 a. % « ## 2 3 4 5 6 7 8 Tree height (m) Fig. 4-4. Relationship between tree height and stems per tree for nest trees and random trees at Moapa, Clark County, Nevada. Linear regression analysis was performed on log- transformed data (nest trees: p = 0.005; adj. = 0.257; random trees: p = 0.742; R^ adj. = 0.0). Graphs depict original data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 Table 4-5. Observed and expected values for random trees and Phainopepla nest trees for four tree structural categories at Moapa, Clark County, Nevada. ,2 _ Tree structural category Short, < 6 stems' Short, > 6 stems" Tall, < 6 stems' Tall, > 6 stems" Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp. Total Random trees 54 49.1 49 46.5 45 52.6 37 36.8 185 Nest trees 2 6.9 4 6.5 15 7.4 5 5.2 26 Total 56 53 60 42 211 a ^ , a ... . , Trees < 4 m tall with & 6 stems. ■ Trees ^ 4 m tall with < 6 stems. * Trees ^ 4 m tall with & 6 stems. Table 4-6. Bonferroni 90% simultaneous confidence intervals for the difference in four tree structural categories between random trees and Phainopepla nest trees at Moapa, Category P ,r P / 90% Cl Selection Short, < 6 stems -0.215 -0.354, -0.076 less use than available Short, > 6 stems -0.111 -0.285, 0.063 no difference Tall, < 6 stems 0.334 0.106, 0.562 more use than available Tall, > 6 stems -0.008 -0.193, 0.177 no difference a ^ . i______structural category. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 Phoradendron clumps also provide excellent shelter and protection from predators (Anderson and Ohmart 1978). Tree height may also be a key factor involved in choice of nest trees. Phainopepla's typical perch is usually the higher branches in the canopy (Laudenslayer 1981), where birds have an unobstructed vantage point for territorial and predator defense. In addition, high perches assist Phainopepla in its habit of hawking insects, which is typical for members and relatives of the flycatcher families (Cowles 1972). Nevertheless, it is important to note that strong correlations among these four variables also demonstrates the typical structure of trees with heavy Phoradendron infection. Those trees that are heavily infected are usually taller and larger than those with little or no Phoradendron infection. In turn, height and size is a reflection of the age of the tree and indicates that older trees contain the heaviest infection. Phainopepla's preference of tall trees with few stems is related to the typical structure of old, undisturbed trees. The multi-stemmed growth form of Prosopis is usually the result of past stress or damage to the tree caused by wood-cutting, fire, herbivory, trampling, and water stress (Heitschmidt et al. 1988, Mooney et al. 1977, Nilsen et al. 1987). Vegetative regrowth after damage to the trunk transforms the original tree into a younger, shorter multi-stemmed shrub or sub-tree with little or no Phoradendron infection. Large trees with fewer stems at Moapa are those that have escaped past disturbance and over time have developed heavy Phoradendron infection. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 Management Implications Breeding success is one of the most important determinants of a population’s fitness (Bock 1997, Krebs 1985). Phainopepla's preference for old growth Prosopis as nesting sites can be related to its breeding success. All five nest failures at Moapa in 1996 and 1997 involved nests that were not built within Phoradendron clumps and occurred low to the ground, while all nests that were built in taller trees within Phoradendron clumps were successful in producing at least one fledged chick. Although it was evident that Phainopepla nested in trees with various structural characteristics, results from this study indicate that old growth Prosopis at the Moapa site is an important component of Phainopepla's preferred habitat and contributes to Phainopepla breeding success in southern Nevada. Management of Prosopis woodlands for Phainopepla habitat should include actions that will maintain or improve Phainopepla reproduction and survival (Martin 1989). Efforts should include reducing disturbance to trees, preventing the loss of old, heavily infected trees, and promoting Prosopis tree recruitment to ensure future replacement of aging woodlands. The determination of Phainopepla's breeding season will assist land managers in planning activities within and adjacent to Prosopis woodlands at times other than the breeding season to avoid disruption of Phainopepla during its nesting period. Although Phainopepla is known to occur in other habitat types in southern Nevada, breeding success has not been documented for any sites other than Moapa. It is hopeful that the determination of Phainopepla breeding success and nest site selection at Moapa will lay the foundation for comparisons with future studies of Phainopepla in southern Nevada. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 Literature Cited American Ornithologists' Union. 1983. Check-Iist of North American birds, 6th ed. American Ornithologists' Union, Washington, DC. 877 pp. Anderson, B. W. and R. D. Ohmart. 1978. Phainopepla utilization of honey mesquite forests in the Colorado River Valley. Condor 80:334-338. Bock, C. E. 1997. The role of ornithology in conservation of the American west. Condor 99:1-6. Cowles, R. B. 1972. Mesquite and mistletoe. Pacific Discovery 25(3): 19-24. Crouch, J. E. 1943. Distribution and habitat relationships of the phainopepla. Auk 60:319-333. Davidson, D. W., W. D. Newmark, J. W. Sites, Jr., D. K. Shiozawa, E. A. Rickart, K. T. Harper, and R. B. Keiter. 1996. Selecting wilderness areas to conserve Utah’s biological diversity. The Great Basin Naturalist 56:95-118. Fisher, C. E. 1977. Mesquite and modem man in southwestern North America. Pages 177-188 in B. B. Simpson (ed.). Mesquite: Its Biology in Two Desert Scrub Ecosystems. US/IBP Synthesis Series 4, Dowden, Hutchinson & Ross, Inc., Stroudsburg, PA. 250 pp. Furlow, F. B. and T. Armijo-Prewitt. 1995. Peripheral populations and range collapse. Conservation Biology 9:1345. Heitschmidt, R. K., R. J. Ansley, S. L. Dowhower, P. W. Jacoby, and D. L. Price. 1988. Some observations from the excavation of mesquite root systems. Journal of Range Management 41:227-231. Hensley, M. M. 1954. Ecological relations of the breeding bird population of the desert biome in Arizona. Ecological Monographs 24:185-207. Jones, K. B. 1990. The status of the phainopepla {Phainopepla nitens); a review of existing data on species biology, distribution and habitat. Unpublished report. 21 pp. Krebs, C. J. 1985. Ecology: The Experimental Analysis of Distribution and Abundance, 3rd ed. Harper & Row, New York, NY. 800 pp. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 Laudenslayer, W. F., Jr. 1981. Habitat utilization by birds of three desert riparian communities. PhD dissertation, Arizona State University. 148 pp. Lesica, P. and F. W. Allendorf. 1995. When are peripheral populations valuable for conservation? Conservation Biology 9:753-760. Lomolino, M. V. And R. Channell. 1995. Splendid isolation: patterns of the geographic range collapse in endangered mammals. Journal of Mammalogy 76:335-347. Marcum, C. L. and D. O. Loftsgaarden. 1980. A nonmapping technique for studying habitat preferences. Journal of Wildlife Management 44:963-968. Martin, T. E. 1992. Breeding productivity considerations: what are the appropriate habitat features for management? Pages 455-473 in J. M. Hagan HI and D. W. Johnston (eds.). Ecology and Conservation o f Neotropical Migrant Landbirds. Smithsonian Institution Press, Washington, D C. Mayfield, H. 1961. Nesting success calculated from exposure. Wilson Bulletin 73:255-261. . 1975. Suggestions for calculating nest success. Wilson Bulletin 87:456-466. Meents, J. K., B. W. Anderson, and R. D. Ohmart. 1984. Sensitivity of riparian birds to habitat loss. Pages 619-625 in R. E. W arner and K. M. Hendrix (eds.). California Riparian Systems: Ecology, Conservation, and Productive Management. University of California Press, Berkeley and Los Angeles, CA. Meinzer, O. E. 1927. Plants as indicators of groundwater. Geological Survey Water- Supply Paper 577, U.S. Government Printing Office, Washington, D C. 95 pp. Mooney, H. A., B. B. Simpson, and O. T. Solbrig. 1977. Phenology, morphology, physiology. Pages 26-43 in B.B. Simpson (ed.). Mesquite: Its Biology in Two Desert Scrub Ecosystems. US/IBP Synthesis Series 4, Dowden, Hutchinson & Ross, Inc., Stroudsburg, PA. 250 pp. Nilsen, E. T., P. W. Rundel, and M. R. Sharifi. 1981. Summer water relations of the desert phreatophyte Prosopis glandulosa in the Sonoran Desert of Southern California. Oecologia 50:271-276. , M. R. Sharifi, R. A. Virginia, and P. W. Rundel. 1987. Phenology of warm desert phreatophytes: seasonal growth and herbivory in Prosopis glandulosa var. rorrgyana (honey mesquite). Journal of Arid Environments 13:217-229. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 5 Ott, R. L. 1993. An Introduction to Statistical Methods and Data Analysis, 4th ed. Duxbury Press, Belmont, CA. 1051 pp. Rand, A. L. and R. M. Rand. 1943. Breeding notes on the phainopepla. Auk 60:333-341. Simpson, B. B. and O. T. Solbrig. 1977. Introduction: the mesquites and algarrobos of Silver Bell and Andalgala. Pages 17-25 in B. B. Simpson (ed.). Mesquite: Its Biology in Two Desert Scrub Ecosystems. US/IBP Synthesis Series 4, Dowden, Hutchinson, & Ross, Inc., Stroudsburg, PA. 250 pp. Snow, D. And B. Snow. 1988. Birds and Berries: a study of an ecological interaction. T & AD Poyser Limited, Staffordshire, England. 268 pp. Walsberg, G. E. 1975. Digestive adaptations of Phainopepla nitens associated with the eating of mistletoe berries. Condor 77:169-174. . 1977. Ecology and energetics of contrasting social systems in Phainopepla nitens (Aves: Ptilogonatidae). Univ. Calif. Publ. Zool. 108:1-63. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTERS THESIS SUMMARY Conclusions Stewart Valley is probably Nevada’s best example of what a Prosopis woodland should look like under optimum conditions. Of the four Prosopis woodlands included in this study, Stewart Valley contains the largest trees with the least evidence of disturbance. Trees are also older and contain, on the average, fewer stems than at the other three sites. The presence of older trees with fewer stems is an indication that trees have not been subject to stress and disturbance that can cause resprouting and premature mortality. Age class distribution is much more even at Stewart Valley, and successful seedling establishment is evidence that the stand is replacing itself. The presence of a confined aquifer and clay soils has created a relatively thick capillary fringe that occurs close to the soil surface. Pahrump also contains clay soils and a confined aquifer, but distance to moist soil is greater than at Stewart Valley. Reasons for this difference were not determined in this study, but one might speculate that soil compaction from heavy human use and the presence of a large number of water wells in the immediate area of Pahrump have influenced the level of the capillary fringe. No significant differences in structural characteristics were detected among the Moapa, Pahrump, and Stump Spring sites, where 96 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 distance to the capillary fringe was similar. However, Stump Spring contained the deepest aquifer at close to 25 m below the soil surface; average tree size at this site was smallest and contained the greatest average number of stems. Proportion of dead trees was also greatest at Stump Spring. Recent seedling establishment was absent at Stump Spring and Moapa. Of the four sites, Moapa supported the greatest species richness for both breeding birds and all species combined. Densities at Moapa were highest in February, March, and April, but Stewart Valley contained higher densities of birds in May and June after Prosopis had fully leafed out. Higher numbers of birds at Moapa earlier in the year indicated that factors other than structure were influencing the avian community; those factors included irrigated agricultural fields adjacent to the woodland, and higher production of Phoradendron berries. No differences were detected in species diversity among the four sites, which is most likely an indication that all four woodlands are similar in structural complexity. This is a reasonable assumption given that all four sites contained monospecific stands of Prosopis with a tree-like growth form. Phainopepla were observed at all four sites, but Moapa was the only site that supported a relatively large breeding population. Phoradendron berry production was greatest at Moapa, and berries persisted on the plant much longer at Moapa than at the other three sites. Pahrump also contained heavy Phoradendron infection, but an extended freezing period in 1990 killed much of the Phoradendron (Cris Tomlinson, pers. commun.), resulting in reduced berry production at this site. Phainopepla at Moapa preferred to nest in larger, older, heavily infected trees with fewer stems. The growth Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 form of Phainopepla's preferred nest trees reflects the typical structure of old, undisturbed trees that have escaped past disturbance and over time have developed heavy Phoradendron infection. Breeding success of Phainopepla was reduced when birds nested lower in the tree and did not build nests within the protection of a Phoradendron clump. Management Recommendations • Disturbance to trees at all sites should be reduced, as damage to the main stem promotes sprouting and changes the growth form from tall trees into smaller, multi-stemmed shrubs. Special attention should be given to Stewart Valley, as this woodland is one of the last remaining representatives of an undisturbed Prosopis stand in southern Nevada. The installation of observation wells at each site will allow long-term monitoring of water table levels, and can be used in future studies of Prosopis physiological response to fluctuating groundwater levels. Future avian studies should include surveys during the summer and winter months, as surveys conducted for this study have furnished only partial information on the avian composition of Prosopis woodlands in southern Nevada. Sampling should be concentrated after full leaf-out of Prosopis in May to better understand the influence of Prosopis structure on avian populations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 Trees at Moapa should be protected from further disturbance, as results of this study have determined that old, undisturbed trees at Moapa are preferred nesting sites for Phainopepla. Activities within and adjacent to the Moapa woodland should be planned around the Phainopepla breeding season to minimize disturbance during the nesting cycle. Soil compaction should be analyzed to determine the extent of compaction at each site. Road access to Prosopis stands should be kept at a minimum, as roads increase soil compaction and the woodlands with easiest access tended to be those subjected to the greatest disturbance. Whereas the effects of gradually declining water tables are long-term and subtle, the effects of wood-cutting are immediate and obvious. Wood-cutting should not be allowed in Prosopis woodlands in southern Nevada, since this is a rare resource that is difficult to replace in arid environments. Fire cannot be eliminated in woodlands, but it should be controlled. The increase of human activities within woodlands can increase the incidence of fire, and frequent, high-intensity fires can increase tree mortality and prevent seedling establishment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 The Moapa site showed no signs of seedling establishment, and very few saplings were found. If objectives are to include management of habitat for breeding Phainopepla, then methods for augmentation of Prosopis tree recruitment should be explored. Studies should also be designed to determine the effects of herbivory on Prosopis seedling survival. The Moapa site is within an active grazing allotment, and rodent and lagomorph populations may be particularly high at this site due to the presence of adjacent agricultural fields. High herbivory pressure at Moapa may be contributing to the lack of seedling establishment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX I MISTLETOE RATING SYSTEM Each tree was divided in half vertically by sight. Each side of the tree was rated for intensity of Phoradendron infection on a scale from 0 to 3: 0 = no infection 1 = light infection 2 = moderate infection 3 = heavy infection Definitions: Light infection: one or two small fist-size clumps Moderate infection: clumps were larger than fist-size or there were more than two clumps, but Phoradendron had not entirely taken over any branch Heavy infection: Phoradendron had taken over an entire branch or large clumps were spread throughout the tree The ratings for both sides of the tree were added together to produce an overall rating system for the tree that ranged from 0 (no infection) to 6 (heavy infection). See following photographs for examples. 101 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 % ; ■ « No Infection 1 + 0 = 1 Light Infection Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 2 + 2 = 4 Moderate Infection 1 3 + 3 = 6 Heavy Infection Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CD ■D O Q. C g Q. ■D CD APPENDIX II (AC/) 3O 0 3 SOIL pH, MINERAL, AND NITROGEN CONTENT AT CD 8 ■D FOUR Prosopis WOODLAND SITES* 3. (O3" 1 3 CD "n 3.c pH Phosphorus (mg/km) Potassium (mg/km) Nitrogen (mg/km) 3" CD Depth MO SV PA SS MO SV PA SS MO SV PA SS MO SV PA SS CD 0.8 ■D 0- 1,5 7.9 8.0 8 1 8.2 3.3 3.8 4.3 400 132 400 400 20.2 2.2 20.8 80 O Q. 1.5- 3.0 8.4 8.0 8.1 8.2 1.2 1.9 2.4 2.8 368 399 400 133 C a O 3.0-4.5 84 8.0 8.2 2.2 1.7 12 400 268 291 3 ■D 4 5-6.0 8.5 8.2 8.2 8.1 1.3 2.7 1.0 2.8 225 242 266 131 O 6.0-7.5 8.4 8.2 8.2 7.9 1.2 1.6 1.2 1.2 202 240 260 57 CD Q. 7.5- 9.0 8.4 8.1 8.2 7.9 1.5 2.1 07 16 221 341 205 61 9.0-10.5 8.1 8.2 ------8.0 1.2 1.5 13 191 232 79 10.5-12.0 8.0 8.2 0.9 0.7 98 246 — ■D CD 12.0-13.5 8.3 8.0 8.2 7.9 6 8 1.5 0.7 09 400 245 208 92 C/) 13.5-15.0 8.0 8.2 8.1 0.9 06 0.8 120 206 114 C/) 15.0-16.5 ------8.2 0.9 184 * Sites arc abbreviated as follows: MO = Moapa; SV = Stewart Valley; PA = Pahrump; S3 = Stump Spring. ■o I Û.s ■o CD APPENDIX III (gC/) 3o" LIST OF AVIAN SPECIES OBSERVED IN FOUR Prosopis WOODLANDS CD 8 5 IN SOUTHERN NEVADA FROM FEBRUARY THROUGH JUNE â' S OF 1996 AND 1997 i 3 CD r C Species Code * Year MO" PA' SS SV' 3- Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Abert's Towhee B 1996 ■OCD Pipilo aberti 1997 X X X X O Û. C American Kestrel R 1996 XX X O Oa LA Falco sparverlus 1997 3 ■O O American Robin B 1996 Turdiis migratorius 1997 X X X X X CD Q. Ash-throated Flycatcher B 1996 XXXXX X X XXXX Myiarchus cinerascens 1997 X X X X X X XXX XXXX O C ■O Bell's Vireo M 1996 CD I'ireo bell il 1997 X C/) W Bewick's Wren B 1996 X X X XXX XX XXXXX X XX XX o" 3 Thryomanes bewickii 1997 X X X X X XX X X X X X X X X Black-headed Grosbeak M 1996 X X Pheucllcus melanocephalus 1997 CD ■D O Q. C 8 Q. ■D CD i. Species Code* Year MO" l'A' SS" SV* w______Feb Mar Apr May Jun Feh Mar Apr May Jun Feh Mar Apr May Jun Feb Mar Apr May Jun = Black-tailed Gnatcaicher B 1996 X X X XXXXX XX a Polloplila melanura 1997 XXXXX X X XXXXX X X 3 CD 0 Black-iluoaud Gray WûTblcr M 1996 X X Dendroica nigrescens 1997 X X X ci' a Black-throated Sparrow B 1996 X X X X X X X X X X X X 1 Amphispiza bilineaia 1997 X X X X X X X X X X X 3 CD ^ Blue Grosbeak M 1996 ^ Guiraca caerulea 1997 X 3. 3" ^ Blue-grayGnaicatcher B 1996 X X X X X X X X X ^ Polioplila caenilca 1997 XX XX XX XXX O Q. Brewer's Sparrow E 1996 X X X X X X a o Spizella breweri 1997 X X X X T3 O Brown headed Cowbird B 1996 X X X X X X X X Mololhnisaier 1997 X XXX XXX XXX (D Q. Bullock's Oriole M 1996 Icterus galbula buUockii 1997 X X o ^ Cactus Wren B 1996 X X X ^ Campylorhynchus brunnelcopllltis 1997 X (7)' 'û. Chipping Sparrow M 1996 p Spizella passerina 1997 X Common Nighthawk B 1996 ChordeÜes minor 1997 O O s CD ■ O O Q. C 8 Q. ■O CD Species Code* Year MO*" PA' SS*^ SV' C/) W Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun o" 3 Common Raven B 1996 X XXX XXXXX 0 Corvus corax 1997 X XX X X X XXX X 3 CD 8 Cooper's Hawk R 1996 X ■D Accipiler cooper! 1997 (O' 3" Crissai Thrasher B 1996 X XX XX X X 1 Toxosloma crissale 1997 X X XX XXXXXX X XXX X X X X 3 CD Dark-eyed Juneo (Oregon subspecies) W 1996 X "n Junco hyemalis oreganus 1997 X XX 3.c 3" CD Dark-cyedJunco(Gray-headed subspecies) W 1996 ■DCD Junco hyemalis canlceps 1997 X O Q. C Empidonax Flycatcher M 1996 X XXXX a Empidonax spp 1997 XX XX XX 3o T3 O Gambel's Quail B 1996 X X XXXX X X X XXX Callipepla gambelli 1997 X XXX X X XXXXX X X (D Q. Golden Eagle 1996 Aquila chrysaelos 1997 Gray Vireo M 1996 T3 (D l'ireo vicinior 1997 c / ) (/) Great Homed Owl 1996 Bubo virglnlanus 1997 X X Greater Roadrunner 1996 XXX X X X Geococcyx caltfornianus 1997 X X X o -J CD ■ O O Q. C 8 Q. CD Species Code* Year MO" PA' SS" SV' C/) C/) ______Feb Mar Apr May Jun Feb Mar Apr May Jun Feh Mar Apr May Jun Feb Mar Apr May Jun Q Hermit Warbler M 1996 X 3" Dendroica occidenlalis 1997 (D 8 House Finch B 1996 XXXXX XXXXX X X X X X X X X 5 Carpodacus mexicamis 1997 XXXXX XX XXX X X X X cq ' 3" Q Ladder backed Woodpecker B 1996 X X S Picoide.1 scalaris 1997 X (D Lark Sparrow B 1996 X X 3 Chondestes grammacus 1997 X X X 3" (D Lesser Nighthawk B 1996 X X ■§ Chordedes acutipennis 1997 X X o Q. ^ Loggerhead Shrike B 1996 o Lamus ludoviclamis 1997 X X 3 T3 O Long eared Owl B 1996 X X CT Asiootiis 1997 I—H (D Q. g Lucy's Warbler B 1996 X X X X X X X X X g Permivora hictae 1997 X X X X X X X X X X X o c T3 MacOilliyray's Warbler M 1996 X X (D Oporornis lolmiei 1997 X (/) Mourning Doye D 1996 X X X X X X X X X X X X Zenaida macroura 1997 XXXXX XXXXX XXX XXXXX Northern Flicker (Red-shaAed race) B 1996 X X X X Colaptes auratus 1997 X X X O 00 ■OCD O Q. C 8 Q. ■O CD (/) Species C ode' _ Year [40® PÂ* ss" ------^ w. Feb1 Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feh Mar Apr May Jun ^ Northern Mockingbird B 1996 X X X X X X X X X X Mimus polyglollos 1997 X X X X X 8 Olive-sided Flycatcher M 1996 ■O Conlopus borealis 1997 Cû3. 3" Orange-crowned Warbler M 1996 i i'ermivora celala 1997 3 CD "n Phainopepla B 1996 X X X X X X c3. Phainopepla nitens 1997 X X X X XXXXX 3" CD Red-tailed Hawk R 1996 CD ■O Biileo Jamaicensis 1997 X X O Q. C Ruby-crowned Kinglet W 1995 X X X X a Begtihis calendula 1997 X X X 3o ■a o Sage Sparrow W 1996 X Amphispiza belli 1997 X X X CD Q. Sage Thrasher W 1996 XX XX XX Oreoscoptes monlaniis 1997 ■O Say's Phoebe E 1996 CD Sayornis sayv 1997 C/) C/) Sharp-shinned Hawk B 1996 Accipiler striatus 1997 X Solitary Vireo M 1996 X Pireo solitarius 1997 o ■o o cû. 8 Û. ■O CD i . Species Code* Year MO^ ÎW S p s F " C/) ______Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun 3 O Spotted Towhee M 1996 X Pipilo mactilalus 1997 8 Townsend's Warbler M 1996 X X X ■O Dendroica townsendi 1997 X X ë' Turkey Vulture R 1996 X X X X o Cathartes aura 1997 X X X 3 CD Verdin B 1996 X X X X X X X X X X X X X X X C A urlpanis Jlaviceps 1997 X X X X X XXX X X X X XXXXX 3- Virginia's Wariber M 1996 X CD ■O I'ermivora virginiae 1997 O Q. C Warbling Vireo M 1996 XX a O Pireo gilvus 1997 X 3 ■D O Western Bluebird W 1996 X X Sialia mexicana 1997 X X CD Q. Western Kingbird B 1996 X XXX Tyrannus verticalls 1997 X Western Tanager M 1996 X X XX ■D CD Piranga ludoviciana 1997 C/) C/) Western Wood-pewee B 1996 X Conlopus sordidulus 1997 X X White crowned Sparrow W 1996 X X X XXXX X Zonotrichia leucophrys 1997 X X X X X X XX CD ■ D O Q. C 8 Q. ■D CD Species Code Year MO PA SS SV C/) C/) Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Wilson's Warbler M 1996 XXXX X X Wilsonia pusilla 1997 X X X 8 Yellow Warbler M 1996 ■O Dendroica petechia 1997 X X X Yellow-breasted Chat B 1996 X X X X X Icleria virens 1997 X Yellow-rumped Warbler (Audubon's race) M 1996 X Dendroica coronala 1997 X X X 3. 3" CD ■DCD O Q. C a 3O ■D O CD Q. ■D CD C/) C/) CD ■ D O Q. C g Q. ■D CD Species Code Year MO PA SS sv C/) (/) Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Feb Mar Apr May Jun Unknowns Unknown Flycaichcr 1996 X XX 1997 X X "O8 ë' Unknown Raptor 1996 X 1997 X X Unknown Sparrow 1996 X X X 1997 X XX 3. 3" Unknown Vireo 1996 X X X XX CD 1997 X X ■DCD O Unknown Warbler 1996 X X Q. X C 1997 X XX a 3O "D Unknown Woodpecker 1996 O 1997 X CD Unknown Passerine 1996 X XXXX XX X X X X X X Q. 1997 X XXX X X X X X X • B = Breeding; E » Edge; M = Migrating; R = Raptor; W = Wintering. Moapa study site. ‘ Pahrump study site. ■D Slump Spring study site. CD • Stewart Valley study site. C/) C/) t o 73 "OCD O Q. C 8 Q. "O CD APPENDIX IV WC/) 3o" O NEST OBSERVATIONS OF Phainopepla nitens ■D8 (O' Site Nest no. Date No. eggs No. chicks No. fledged Days to fledge Nest ht (m) Nest in mistletoe mo 96-1 04/05/96 2 0 0 1.10 no mo 96-1 04/08/96 0 2 0 mo 96-1 04/12/96 0 2 0 3. mo 96-1 04/15/96 0 2 3" 0 CD mo 96-1 04/17/96 0 2 0 ■DCD O mo 96-1 04/19/96 0 2 0 Q. C mo 96-1 04/26/96 0 2 0 Oa 3 mo 96-1 04/29/96 0 0 2 20-23 ■D O mo 96-2 04/07/96 2 0 0 1.78 no mo 96-2 04/08/96 2 0 0 CD Q. mo 96-2 04/12/96 2 0 0 mo 96-2 04/15/96 0 2 0 mo 96-2 04/17/96 0 2 0 ■D CD mo 96-2 04/19/96 0 2 0 (/) mo 96-2 04/26/96 0 0 0 failed mo 96-3 04/07/96 1 0 0 1.59 no mo 96-3 04/08/96 2 0 0 mo 96-3 04/12/96 2 0 0 7 3 CD ■ D O Q. C 8 Q. ■D CD Site Nest no. Date No. eees No. chicks No. fledeed Davs to fledee Nest ht fm'l Nest in mistletoe WC/) mo 96-3 04/15/96 2 0 0 3o" mo 96-3 04/17/96 2 0 0 mo 96-3 04/19/96 0 0 0 failed "O8 mo 96-4 04/08/96 2 0 0 3.42 yes mo 96-4 04/12/96 2 0 0 mo 96-4 04/15/96 0 2 0 mo 96-4 04/17/96 0 2 0 mo 96-4 04/26/96 0 2 0 3. mo 96-4 04/29/96 0 2 0 3" CD mo 96-4 05/01/96 0 2 0 ■DCD O mo 96-4 05/03/96 0 2 0 Q. C mo 96-4 05/07/96 0 0 2 20-24 Oa 3 mo 96-5 04/12/96 1 1 0 3.76 yes ■D O mo 96-5 04/15/96 1 1 0 mo 96-5 04/17/96 1 1 0 CD Q. mo 96-5 04/19/96 1 1 0 mo 96-5 04/26/96 1 1 0 mo 96-5 04/29/96 1 1 0 ■D CD mo 96-5 05/01/96 1 1 0 C/) C/) mo 96-5 05/03/96 1 1 0 mo 96-5 05/07/96 0 0 1 22-25 mo 96-6 04/17/96 0 2 0 1.08 no mo 96-6 04/19/96 0 2 0 7 3 CD ■ D O Q. C 8 Q. ■D CD Site Nest no. Date No. eees No. chicks No. fledeed Davs to fledee Nest ht (m) Nest in mistletoe WC/) 3o" mo 96-6 04/26/96 0 2 0 O mo 96-6 04/29/96 0 2 0 3 CD mo 96-6 05/01/96 0 2 0 8 mo 96-6 05/03/96 0 2 0 mo 96-6 05/07/96 0 0 2 7 mo 96-7 04/17/96 0 2 0 2.46 no CD mo 96-7 04/19/96 0 2 0 mo 96-7 04/26/96 0 0 2 7 3. 3" 04/19/96 0 2 0 no CD mo 96-8 2.16 mo 96-8 04/29/96 0 2 0 ■DCD O mo 96-8 05/01/96 0 2 0 Q. C a mo 96-8 05/03/96 0 2 0 O 3 mo 96-8 05/07/96 0 0 2 ■D ? O mo 96-9 04/19/96 0 2 0 5.08 yes 7 CD mo 96-9 04/29/96 0 0 2 Q. mo 96-10 04/19/96 0 2 0 3.16 yes mo 96-10 04/26/96 0 2 0 ■D mo 96-10 04/29/96 0 2 0 CD mo 96-10 05/01/96 0 2 0 C/) C/) mo 96-10 05/03/96 0 2 0 mo 96-10 05/07/96 0 2 0 mo 96-10 05/08/96 0 2 0 mo 96-10 05/13/96 0 0 2 7 7 3 CD ■ D O Q. C 8 Q. ■D CD Site Nest no. Date No. eggs No. chicks No. fledeed Davs to fledge Nest ht Cm) Nest in mistletoe WC/) 3o" mo 97-1 03/20/97 2 0 0 2.97 yes O mo 97-1 03/24/97 0 2 0 mo 97-1 03/27/97 0 2 0 8 mo 97-1 03/31/97 0 2 0 mo 97-1 04/03/97 0 2 0 mo 97-1 04/07/97 0 2 0 CD mo 97-1 04/10/97 0 2 0 mo 97-1 04/14/97 0 1 1 19-24 3. 3" mo 97-1 04/18/97 0 0 2 CD mo 97-2 03/19/97 2 0 0 2.56 no ■DCD O mo 97-2 03/20/97 2 0 0 Q. C a mo 97-2 03/27/97 2 0 0 O 3 mo 97-2 03/31/97 0 2 0 "D O mo 97-2 04/03/97 0 2 0 mo 97-2 04/07/97 0 2 0 CD Q. mo 97-2 04/10/97 0 2 0 mo 97-2 04/14/97 0 2 0 ■D mo 97-2 04/18/97 0 2 0 CD mo 97-2 04/21/97 0 0 2 19-24 C/) C/) mo 97-3 03/19/97 2 0 0 3.29 yes mo 97-3 03/20/97 2 0 0 mo 97-3 03/24/97 0 2 0 mo 97-3 03/27/97 0 2 0 ON CD ■ D O Q. C g Q. ■D CD Site Nest no. Date No. eggs No. chicks No. fledged Davs to fledge Nest ht tml Nest in mistletoe WC/) 3o" mo 97-3 03/31/97 0 2 0 O mo 97-3 04/01/97 0 2 0 3 CD mo 97-3 04/03/97 0 2 0 8 ■D mo 97-3 04/07/97 0 2 0 ci' mo 97-3 04/10/97 0 2 0 mo 97-3 04/14/97 0 0 2 18-24 mo 97-3 04/18/97 0 0 2 mo 97-3 04/21/97 0 0 2 3. 3" mo 97-4 03/19/97 2 0 0 1.82 no CD mo 97-4 03/20/97 2 0 0 ■DCD O mo 97-4 03/24/97 2 0 0 Q. C mo 97-4 03/27/97 2 0 0 Oa 3 mo 97-4 03/31/97 0 2 0 ■D O mo 97-4 04/07/97 0 2 0 mo 97-4 04/10/97 0 2 0 CD Q. mo 97-4 04/14/97 0 2 0 mo 97-4 04/18/97 0 2 0 ■D mo 97-4 04/21/97 0 2 0 CD mo 97-4 04/24/97 0 0 2 22-27 C/) C/) mo 97-5 03/19/97 2 0 0 2.58 no mo 97-5 03/20/97 2 0 0 mo 97-5 03/24/97 1 1 0 mo 97-5 03/27/97 1 1 0 CD ■ D O Q. C g Q. ■D CD Site Nest no. Date No. eees No. chicks No. fledeed Davs to fledee Nest ht /m'I Nest in mistletoe WC/) 3o" mo 97-5 03/31/97 1 1 0 O mo 97-5 04/03/97 1 1 0 mo 97-5 04/07/97 1 1 0 ■D8 mo 97-5 04/10/97 1 1 0 mo 97-5 04/14/97 1 0 1 18-24 mo 97-5 04/18/97 1 0 1 CD mo 97-6 03/19/97 0 2 0 4.13 yes mo 97-6 03/20/97 0 2 0 3. 3" mo 97-6 03/24/97 0 2 0 CD mo 97-6 03/27/97 0 0 2 ? ■DCD O mo 97-6 03/31/97 0 0 2 Q. C mo 97-6 04/03/97 0 0 2 a O 3 mo 97-6 04/07/97 0 0 2 ■D O mo 97-6 04/10/97 0 0 2 mo 97-6 04/14/97 0 0 2 CD Q. mo 97-6 04/21/97 0 0 2 mo 97-7 03/20/97 2 0 0 1.03 no ■D mo 97-7 03/24/97 0 2 0 CD mo 97-7 03/27/97 0 2 0 C/) C/) mo 97-7 03/31/97 0 2 0 mo 97-7 04/03/97 0 2 0 mo 97-7 04/07/97 0 2 0 mo 97-7 04/10/97 0 0 2 15-20 00 CD ■ D O Q. C g Q. ■D CD WC/) Site Nest no. Date No. eees No. chicks No. fledeed Davs to fledee Nest ht Cm') Nest in mistletoe o" 3 mo 97-7 04/14/97 0 0 2 O mo 97-8 03/20/97 2 0 0 2.05 no 8 mo 97-8 03/24/97 2 0 0 mo 97-8 03/27/97 0 2 0 mo 97-8 03/31/97 0 2 0 mo 97-8 04/03/97 0 2 0 mo 97-8 04/07/97 0 2 0 mo 97-8 04/10/97 0 2 0 3. 3" CD mo 97-8 04/14/97 0 0 2 15-20 ■DCD mo 97-8 04/18/97 0 0 2 O Q. mo 97-9 03/20/97 0 2 0 3.93 yes C a O mo 97-9 03/24/97 0 2 0 3 ■D mo 97-9 03/27/97 0 2 0 O mo 97-9 03/31/97 0 2 0 CD mo 97-9 04/03/97 0 0 2 ? Q. mo 97-9 04/07/97 0 0 2 mo 97-9 04/10/97 0 0 2 ■D CD mo 97-9 04/18/97 0 0 2 mo 97-9 04/21/97 0 0 2 C/) C/) mo 97-10 03/20/97 0 2 0 3.96 yes mo 97-10 03/24/97 0 2 0 mo 97-10 03/27/97 0 2 0 mo 97-10 03/31/97 0 0 2 ? VO ■OCD O Q. C g Q. "O CD Site Nest no. Date No. eees No. chicks No. fledeed Davs to fledee Nest ht (ml Nest in mistletoe C/)W 3o" mo 97-10 04/03/97 0 0 2 O mo 97-10 04/07/97 0 0 2 3 CD mo 97-10 04/10/97 0 0 2 8 "O mo 97-10 04/14/97 0 0 2 (O' mo 97-10 04/18/97 0 0 2 mo 97-11 03/24/97 7 7 0 4.94 yes mo 97-11 03/27/97 ? 7 0 mo 97-11 03/31/97 ? 7 0 3. 3" mo 97-11 04/03/97 7 7 0 CD mo 97-11 04/07/97 7 ? 0 ■DCD O mo 97-11 04/10/97 ? 7 0 Q. C mo 97-11 04/14/97 7 ? 7 7 Oa 3 mo 97-11 04/18/97 ? ? 7 7 ■D O mo 97-12 04/21/97 0 2 0 1.01 no mo 97-12 04/24/97 0 2 0 CD Q. mo 97-12 04/28/97 0 2 0 O mo 97-12 05/02/97 0 0 2 7 C "O mo 97-13 04/21/97 2 0 0 2.75 no CD mo 97-13 04/24/97 2 0 0 (/) (/) mo 97-13 05/02/97 2 0 0 mo 97-13 05/05/97 0 0 0 failed mo 97-14 04/24/97 2 0 0 1.00 no mo 97-14 04/28/97 2 0 0 lO o CD ■ D O Q. C g Q. ■O CD Site Nest no. 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Effect of fire on honey mesquite. Joumal of Range Management 29:467-471. Wright, R. A. 1982. Aspects of desertification in Prosopis dunelands of southem New Mexico, U.S.A. Joumal of Arid Environments 5:277-284. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VTTA College of Science and Mathematics University of Nevada, Las Vegas Jeri Brastrup Krueger Home Address: 6561 Canyon Cove Way Las Vegas, NV 89108 Degrees: Bachelor of Science, Wildlife Biology, 1993 Colorado State University, Ft. Collins Special Honors and Awards: Graduated Summa Cum Laude, December 1993 College of Natural Resources Colorado State University, Ft. Collins President’s Scholarship, 1991, 1992, 1993 Colorado State University, Ft. Collins Philip A. Connolly Memorial Scholarship, 1992 Colorado State University, Ft. Collins Career Advancement Scholarship, Business and Professional Women’s Foundation, 1992 Colorado State University, Ft. Collins Thesis Title: A Comparative Study of Honey Mesquite Woodlands in Southem Nevada and Their Use by Phainopeplas and Other Avian Species Thesis Examination Committee: Chairperson, Dr. Charles Douglas, Ph. D. Committee Member, Dr. Stan Smith, Ph. D. Committee Member, Dr. Donald Baepler, Ph. D. Graduate Faculty Representative, Dr. Evangelos Yfantis, Ph. D. 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMAGE EVALUATION TEST TARGET (Q A-3) 1.0 Ifia m 2.2 ÎT 11* [ 2.0 l.l 1.8 1.25 1.4 1.6 150mm V «P.7 /qPPLIED ^ IIVHGE . Inc 1653 East Main Street Rochester. NY 14609 US.4 y Phone: 716/482.0300 Fax: 716/288-5989 O 1993. Applied Image. Inc.. Ail Rights Reserved > y Reproduced with permission of the copyright owner. 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