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Vulnerability of Species to Climate Change in the Southwest: Threatened, Endangered, and At-Risk Species at the Barry M. Goldwater Range, Arizona
Abstract and Figures
AbstrAct Future climate change is anticipated to result in ecosystem changes, and consequently, many species are expected to become increasingly vulnerable to extinction. This scenario is of particular concern for threatened, endangered, and at-risk species (TER-S) or other rare species. The response of species to climate change is uncertain and will be the outcome of complex interactions and processes. Nevertheless, a simple flexible strategy is needed to help integrate climate change into management planning and actions. This assessment uses SAVS, an assessment tool based on ecological principals, to rank individual species of interest within the eastern portion of the Barry M. Goldwater Range, Arizona, according to predicted climate change responses and associated population declines balanced with responses expected to incur resilience or population increases. Further, specific areas of vulnerability, research needs, and management implications are identified for each species in detailed species accounts. Based solely on predicted response to climate change, Sonoran pronghorn (Antilocapra americana sonoriensis) and desert tortoise (Gopherus morafkai) are the most vulnerable to population declines. Results also suggest that climate change will make management of some TER-S species more difficult. Several critical management areas are identified that can mitigate negative impacts to benefit multiple species, including fire and fuels, invasive species, natural and artificial waters, and landscape-scale planning. Management planning should be in place that will assist species impacted by extreme events such as prolonged drought, severe wildfires, and/or intense flooding. The assessment process was also used to identify areas where climate change may present opportunities, as opposed to challenges, for species management.
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... This species was expected at BMGR-W and was considered a high priority for monitoring (Villarreal et al. 2011) but had not been previously documented from the range. It is thought to be particularly susceptible to climate change at BMGR (Bagne & Finch 2012). Spadefoots spend much of their lives underground in dry habitats, emerging only briefly after saturating monsoon rains. ...
... We confirmed the continuing occurrence of this species in 2017 with one sighting of a live tortoise in the north part of the Copper Mountains, and some remains in the west Copper Mountains and in the Gila Mountains. This is the most vulnerable reptile to climate change on the BMGR (Bagne & Finch 2012). The federally-listed Mohave Desert Tortoise, Gopherus agassizii, has been reported on the BMGR-W (Petersen et al. 2017) but this is in error, a reference to out-of-date taxonomy. ...
... Since the split has not yet been widely recognized, we consider the species together here. U. rufopunctata (in the broad sense) is considered to be the second most vulnerable species to climate change on the BMGR (Bagne & Finch 2012), and is currently under review for federal listing. The Colorado Fringe-toed Lizard (U. notata) has been reported on the range (Petersen et al. 2017) but this is in error, a reference to out-of-date taxonomy. ...
The Barry M. Goldwater Range–West (BMGR-W) includes 700,000 acres of Sonoran Desert
near Yuma, Arizona. The Integrated Natural Resources Management Plan for the BMGR-W
requires that baseline conditions for small mammals, reptiles, and amphibians be established so that natural resource managers may determine how best to allocate effort to protect natural resources. Little is known about the small mammals, reptiles, and amphibians of the BMGR-W. What is currently known about these animals comes from either short term surveys at small locations or species-specific monitoring range-wide. We conducted a four-year inventory from 2016 to 2019 to ensure that wildlife resources will be identified, protected, and managed in compliance with regulatory requirements for significant or sensitive species, including federal threatened and endangered species. The objectives of this project were: 1) to establish a repeatable monitoring methodology that will capture the diversity found in small mammals, reptiles, and amphibians on the BMGR-W, 2) develop distribution maps for those species, and 3) provide recommendations for monitoring efforts and natural resource stewardship to assist the military mission on the BMGR-W. We sampled for amphibians and reptiles using visual encounter surveys by foot and vehicle, using drift fences with pitfall and funnel traps, setting cover board arrays, and setting automated recording devices to record anuran calls. We sampled for small mammals by setting trapping grids of Sherman traps and Tomahawk traps. Here we document 24 species of small mammals and 40 species of amphibians and reptiles from the range, including several unexpected or special concern species.
... This species was expected at BMGR-W and was considered a high priority for monitoring (Villarreal et al. 2011) but had not been previously documented from the range. It is thought to be particularly susceptible to climate change at BMGR (Bagne & Finch 2012). Spadefoots spend much of their lives underground in dry habitats, emerging only briefly after saturating monsoon rains. ...
... We confirmed the continuing occurrence of this species with one sighting of a live tortoise in the north part of the Copper Mountains, and some remains in the west Copper Mountains and in the Gila Mountains. This is considered to be the reptile that is most vulnerable to climate change on the BMGR (Bagne & Finch 2012 ...
... The most recent phylogeny (Gottscho et al. 2017) follows the suggestion of Trépanier and Murphy (2001) in considering the Mohawks Dunes population to be an as yet unnamed species distinct from U. rufopunctata. This is considered to be the second most vulnerable species to climate change on the BMGR (Bagne & Finch 2012), and is currently under review for federal listing. The Colorado Fringe-toed Lizard (Uma notata) has been reported on the range (Petersen et al. 2017) but this is in error, likely a reference to out-of-date taxonomy. ...
The Barry M. Goldwater Range-West (BMGR-W) includes 283,280 ha of Sonoran Desert near Yuma, Arizona. The Integrated Natural Resources Management Plan (INRMP) for the BMGR-W requires that baseline conditions for small mammals, reptiles, and amphibians be established so that natural resource managers may determine how best to allocate effort to protect natural resources. Little is known about the small mammals, reptiles, and amphibians of the BMGR-W. What is currently known about these animals comes from either short term surveys at small locations or species-specific monitoring range-wide. We are conducting an inventory to ensure that wildlife resources will be identified, protected, and managed in compliance with regulatory requirements for significant or sensitive species, including federal threatened and endangered species. The objectives of this project are: 1) to establish a repeatable baseline monitoring methodology that will capture the diversity found in small mammals, reptiles, and amphibians on the BMGR, 2) develop potential distribution maps for those species, and 3) provide recommendations for monitoring efforts and natural resource stewardship to assist the military mission on the BMGR. We surveyed for amphibians, reptiles, and small mammals by conducting 30,800 km of visual encounter surveys in all five general habitat types present on the range. Additionally, we sampled for small mammals by setting trapping grids of Sherman traps (11,391 trap-nights) and Tomahawk traps (1,092 trap-nights). We sampled for amphibians and reptiles by setting drift fences with box and pitfall traps for a total of 379 fence-nights. Here we document 23 species of small mammals and 40 species of amphibians and reptiles from the range, including several unexpected or special concern species. We conclude with plans and priorities for future work to improve the completeness of this inventory.
... The Barry M. Goldwater range was established in 1941 for military training and is used by the United States Air Force and Marine Corps for air-to-air and air-to-ground aircraft maneuvers, laser testing, and field training exercises (BMGR Fact Sheet, 2009 Annually the range receives three to nine inches of rain (BMGR Fact Sheet, 2009). Depending on the region of the range summer temperatures can vary from 100°F to 109°Fand winter temperatures varying from 40°F to 50°F, (Bagne and Finch, 2010;Western Regional Climate Center,2011). The Barry M. Goldwater Range is in an aridic soil moisture regime and a hyperthermic soil temperature regime, causing the soils to be primarily Aridisols (Soil Survey Staff, Natural Resource Conservation Service, 2011). ...
... The Aguila and Growler Mountains which serve as the eastern boundary of the San Cristobal Valley represent this type of mountain, but are not included in this study area. The range provides habitat for diverse flora and fauna, including several endangered and threatened species such as; Antilocapra americana sonoriensis (Sonoran pronghorn antelope), Glaucidium brasilianum cactorum (cactus ferruginous pygmy owl), Phrynoso mamcallii (flat-tailed horned lizard), and Leptonycteris curasoae (lesser long-nosed bat) (Bagne and Finch, 2010;BMGR Fact Sheet, 2009 ...
... To our knowledge, no systematic comparison of the results of different approaches to assessing vulnerability to climate change has been undertaken. Many agencies and local conservation groups have already incorporated results from these various assessments into climate change management reports and policies within the eastern United States (e.g., Young et al. 2009, Bagne and Finch 2010, Dubois et al. 2011, Schlesinger et al. 2011, Brinke and Jones 2012. Given that no 2 assessment approaches available to date use the same combination of variables, or frame their questions in the same way, it is possible that these approaches produce different results for the same species. ...
... Many climate change vulnerability assessments are now being used to identify and inform management actions for species and ecosystems (e.g., Young et al. 2009, Bagne and Finch 2010, Lin and Morefield 2011, Schlesinger et al. 2011, Brinke and Jones 2012. Lack of a common assessment, or a common evaluation technique or outcome, have led to the development of a variety of methodologies for calculating vulnerability. ...
The need for wildlife climate change vulnerability and sensitivity assessments has increased over the past decade. Use of these assessments by wildlife and land managers has increased due to concern for potential effects of climate change on species and landscapes. Although many approaches exist for assessing sensitivity and vulnerability to climate change, little is known about the similarity of results between methods. We compared outputs of 3 widely available assessments for the western United States: the NatureServe Climate Change Vulnerability Index, the U.S. Forest Service System for Assessing the Vulnerability of Species, and the Climate Change Sensitivity Database. We performed a broad categorical comparison and examined correlations across rankings to compare assessment outputs. We found little agreement in species rankings between pairs of assessments. There is no apparent pattern within, or between, taxa or habitat associations that could explain this poor correlation. Disparities likely result from differences in question format, choice of data input, or how vulnerability or sensitivity is calculated. Consideration of vulnerability quantification is needed, particularly regarding species sensitivity and adaptive capacity, because of limited understanding of species and community responses to climate exposure. Our results indicate it is extremely important to be aware of the specific goal and the quality, quantity, and variety of data used in each individual assessment in order to adequately use these assessments as tools for management planning. With the increasing need to include climate change scenarios in management actions and decisions, we suggest that increased cooperation among assessment developers could greatly aid in eliminating this discrepancy. © 2014 The Wildlife Society
... prodServices/climatechange/ccvi.jsp), designed for both plant and animal species, was used in Nevada and Massachusetts (Galbraith and O'Leary 2011;Young and others 2011); and SAVS, a System for Assessing Vulnerability of Species to climate change (Bagne and others 2011), was used to assess terrestrial vertebrate species in New Mexico (Finch and others 2011;Friggens and others, in prep.) and Arizona (Bagne and Finch 2010;Coe and others, in prep.). On a broader scale, the Environmental Protection Agency has a scoring system that has been applied nationally to assess the combined impact of climate change and non-climate related vulnerabilities for threatened and endangered species (Galbraith and Price 2011;U.S. EPA 2009). ...
Recent research and species distribution modeling predict large changes in the distributions of species and vegetation types in the western interior of the United States in response to climate change. This volume reviews existing climate models that predict species and vegetation changes in the western United States, and it synthesizes knowledge about climate change impacts on the native fauna and flora of grasslands, shrublands and deserts of the interior American West. Species' responses will depend not only on their physiological tolerances but also on their phenology, establishment properties, biotic interactions, and capacity to evolve and migrate. The volume is divided into eight chapters that cover the topics of carbon mitigation and adaptation. Current and likely responses of species and habitats to climate change are examined in relation to taxonomic group and ecoregion and with regard to other disturbances. The volume ends with a review of management decision support needs and tools for assessing vulnerability of natural resources and conserving and restoring ecosystems that are or may be impacted by climate change.
... Following the 2002 drought, a captive breeding pen for Sonoran pronghorn was initiated on the Cabeza Prieta National Wildlife Refuge (CPNWR) to facilitate recovery efforts (Otte 2006). Natural surface water in the region is limited (USFWS 2010, Bagne andFinch 2012); therefore, old livestock water tanks and building catchments were improved and developed into artificial water sources (drinkers) for pronghorn and desert bighorn sheep (Ovis canadensis nelsoni). Today, approximately 159 individuals exist in the U.S. population, and 2 separate populations in Sonora, Mexico contain approximately 220 total individuals. ...
The Sonoran pronghorn (Antilocapra americana sonoriensis) is a subspecies of pronghorn found exclusively in the Sonoran Desert of Arizona (USA) and Mexico. Sonoran pronghorn persist at low densities and are geographically isolated from other pronghorn populations. Numbers have declined in recent decades, but the population has rebounded from a low of fewer than 50 animals in 2003 to an estimated 159 individuals in 2012; however, little is known about population demographics beyond abundance estimates. We developed a species identification test that uses mitochondrial DNA (mtDNA) species-specific primers to distinguish between sympatric Sonoran pronghorn and mule deer (Odocoileus hemionus) using DNA extracted from fecal pellets. We accurately identified each species in 100% of the blood and tissue reference samples. We also evaluate the rate of DNA degradation in pronghorn fecal samples ranging from 1 day to 124 days old and document that mtDNA species identification success rates were 100% through day 14. Success rates dropped to 95% by day 21, 50% on day 60, and 10% by day 124. This new test will be a valuable tool for documenting the presence of Sonoran pronghorn across their current range and can also be used for other pronghorn populations. © 2014 The Wildlife Society.
... prodServices/climatechange/ccvi.jsp), designed for both plant and animal species, was used in Nevada and Massachusetts (Galbraith and O'Leary 2011;Young and others 2011); and SAVS, a System for Assessing Vulnerability of Species to climate change (Bagne and others 2011), was used to assess terrestrial vertebrate species in New Mexico (Finch and others 2011;Friggens and others, in prep.) and Arizona (Bagne and Finch 2010;Coe and others, in prep.). On a broader scale, the Environmental Protection Agency has a scoring system that has been applied nationally to assess the combined impact of climate change and non-climate related vulnerabilities for threatened and endangered species (Galbraith and Price 2011;U.S. EPA 2009). ...
We examine the interactions between climate change and natural and anthropogenic disturbances in grassland, shrubland, and desert ecosystems of the Interior West. Disturbances such as fire, drought, grazing, urbanization, and energy development are predicted to have a heightened impact on the western United States under a changing climate. We identify key issues related to these predictions, and provide examples of research that the RMRS GSD Ecosystems Program is conducting to address many of these predictions, as well as identify future research needs.
Climate-change impacts to Department of Defense (DoD) installations will challenge military mission and natural resource stewardship efforts by increasing vulnerability to flooding, drought, altered fire regimes, and invasive species. We developed biome classifications based on current climate for the coterminous United States using the Holdridge Life Zone system to assess potential change on DoD lands. We validated classifications using comparisons to existing ecoregional classifications, the distribution of major forest types, and tree species in eastern North America. We projected future life zones for mid- and late-century time periods under three greenhouse gas emission scenarios (low—B1, moderate—A1B, and high—A2) using an ensemble of global climate models. To assess installation vulnerability (n = 529), we analyzed biome shifts using spatial cluster analysis to characterize interregional variation, and identified representative installations for subsequent landscape-level analyses. Although mean annual temperatures are expected to increase, installations located in the Northeast, Lake States, and western Great Plains are likely to experience the largest proportional increases in temperature. Accordingly, forest and grassland communities at these installations managed to support a wide range of training, and environmental objectives may be adversely affected by altered disturbance regimes, heat, and moisture stress. However, precipitation is projected to increase in the Northeast and Lake States mitigating some effects of increased temperatures on biological communities. Given the uncertain response to climate change in different ecoregions, additional environmental and stewardship attributes are needed within a decision-support framework to understand vulnerabilities and provide appropriate responses.
people fail to realize that real communication goes in both directions." Lee Iacocca spoke these wise words about the failings of business, but clearly there is a lesson here for management of natural resources as well. Scientists are doing research every day that improves our understanding of our valued resources. But work does not stop at simply conducting an experiment, but needs to include effective communication of results that are relevant to managers. Scientists listen closely to what managers have to say and design studies to address questions across the diverse array of issues that challenge management goals today. Helping managers to promote sustainability on the Nation's forests and grasslands has been an overarching goal of US Forest Service Research and Development from the agency's beginnings in 1905. Major advances in resource management have been made with the help of science, from increasing yields of commodities like timber and cattle to providing services such as camping and clean water. But what steps should be taken to protect the public's resources? Some traditional applications of science in management are the development of best management practices to balance resource utilization with ecological function and support for decisions made in environmental assessments. Jan Engert, RMRS Assistant Director for Science Application and Integration, notes, "An emerging challenge for land management today is climate change. Climate change in particular is full of complexity and uncertainty, which makes decision-making and planning more difficult. A scientific approach is a powerful way to help tease apart that complexity, reduce critical uncertainties, and pinpoint effective solutions."
Fire, other disturbances, physical setting, weather, and climate shape the structure and function of forests throughout the Western United States. More than 80 years of fire research have shown that physical setting, fuels, and weather combine to determine wildfire intensity (the rate at which it consumes fuel) and severity (the effect fire has on vegetation, soils, buildings, watersheds, and so forth). As a result of fire exclusion, timber harvesting, and livestock grazing, millions of acres of forestlands (mainly in dry forests dominated by ponderosa pine and/or Douglas-fir) contain a high accumulation of flammable fuels compared to conditions prior to the 20th century. Forests with high stem density and fuel loading combined with extreme fire weather conditions have led to severe and large wildfires (such as those seen in the summers of 2000 and 2002 and the fall of 2003) that have put a number of important values at risk. Although homes in the path of a wildfire are perhaps the most immediately recognized value, these wildfires also put numerous other human and ecological values at risk, such as power grids, drinking water supplies, firefighter safety, critical habitat, soil productivity, and air quality.
For a given set of weather conditions, fire behavior is strongly influenced by stand and fuel structure. Crown fires in the dry forest types represent an increasing challenge for fire management as well as a general threat to the ecology of these forests and the closely associated human values. Crown fires are dependent on the sequence of available fuels starting from the ground surface to the canopy. Limiting crown fire in these forests can, thus, be accomplished by fuel management actions that first reduce surface and ladder fuels before manipulating canopy fuels. Reducing crown fire and wildland fire growth across landscapes decreases the chances of developing large wildfires that affect human values adjacent to forested areas. However, a narrow focus on minimizing crown fire potential will not necessarily reduce the damage to homes and ecosystems when fires do occur there. Homes are often ignited by embers flying far from the fire front, and by surface fires. Fire effects on ecosystems can also occur during surface fires where fine fuels and deep organic layers are sufficient to generate high temperatures for long periods.
Fuel treatments can help produce forest structures and fuel characteristics that then reduce the likelihood that wildfires will cause large, rapid changes in biophysical conditions. Fuel treatments can also help modify fire behavior sufficiently so that some wildfires can be suppressed more easily. Subsequent, sustained fuel treatments can maintain these conditions. Different fuel reduction methods target different components of the fuel bed. Thinning mainly affects standing vegetation, and other types of fuel treatments such as prescribed fire and pile burning woody fuels are needed to modify the combustion environment of surface fuels. In forests that have not experienced fire for many decades, multiple fuel treatments-that is, thinning and surface fuel reduction-may be required to significantly affect crown fire and surface fire hazard. Fuel treatments cannot guarantee benign fire behavior but can reduce the probability that extreme fire behavior will occur. Fuel treatments can be designed to restore forest conditions to a more resilient and resistant condition than now exists in many forests, and subsequent management could maintain these conditions, particularly in dry forests (ponderosa pine and Douglas-fir) where crown fires were infrequent. The degree of risk reduction will depend to some degree on the level of investment, social and economic acceptability of treatments, and concurrent consideration of other resource values (for example, wildlife).
This report describes the kinds, quality, amount, and gaps of scientific knowledge for making informed decisions on fuel treatments used to modify wildfire behavior and effects in dry forests of the interior Western United States (especially forests dominated by ponderosa pine and Douglas-fir). A review of scientific principles and applications relevant to fuel treatment primarily for the dry forests is provided for the following topics: fuels, fire hazard, fire behavior, fire effects, forest structure, treatment effects and longevity, landscape fuel patterns, and scientific tools useful for management and planning.
A population of Uma notata inornata Cope near Palm Springs, Riverside Co., California, was studied. Sand lizards are closely confined to aeolian sand deposits. They regularly bury 0.5-4 cm beneath the sand surface to escape predators and, to some extent, to avoid extremes of temperature. They do not bury deep enough to avoid the highest temperatures of midsummer; instead they emerge and seek shade on the surface. When escaping from predators, sand lizards are unselective regarding burying sites. They are more selective in their nocturnal retreat in which they bury at the windward end of small accretion dunes. In laboratory choice experiments lizards preferred sand from the windward ends of these dunes to coarser or finer sand. The branches and leaves of partially buried shrubs may protect the lizards from predators and reduce the pressure of the overlying sand. Field observations suggest that sand lizards are less plentiful in areas of coarse sand or sand containing a large admixture of silt. In the laboratory, lizards avoided burying in such substrates. Uma is an inefficient burrower compared to some Old World arenicolous lizards. Its adaptations specifically for burrowing are largely behavioral. The morphological features which are adaptive for its burrowing behavior are characteristic of the entire Uma-Callisaurus-Holbrookia stock.
We analyzed infrared video recordings from a maternity roost in southwestern Arizona to determine social behavior and time and activity budgets of adult Leptonycteris curasoae (Chiroptera: Phyllostomidae) for 2 weeks late in the nursing period. Between 2000 and 0330 h, females nursed their young an average of two times for a total of ca. 52 min. Females nursed only their own babies; they occasionally interacted with other young and adults, most frequently by touching noses. Adults returned to and left their young independently of each other, not in synchronized fashion. Between 0500 and 1900 h, adults seldom interacted, although they were clustered tightly. Young were in a nursing position, presumably nursing, ca. 50% of the time. Adults never appeared to sleep and spent 74% of the day quietly alert and 24% grooming themselves. We observed no cooperative behavior such as allogrooming, communal nursing, or sharing of food at any time. We suggest that absence of stable associations of adults caused by long-distance migration and occasional changes in roosting sites has prevented evolution of overtly cooperative behavior in dayroosts of L. curasoae.
Evaluates the view that drinking water is a limiting factor to many desert animals, and criticises the consequent wildlife management policy of increasing the availability of water in the US Southwest. Managers in the Cabeza Prieta National Wildlife Refuge and the W part of the Goldwater Air Force Range in SW Arizona, for example, have increased the number of waterholes in desert bighorn Ovis canadensis mexicanus habitats by 33% and the maximum quantity of water by 364%. Such developments are not necessarily beneficial, and indeed may have some harmful consequences. Bighorn do not move far to find water, for instance, and many waterholes have been ineffectually located. Further work is needed to correlate water provision with bighorn population growth and range expansion, which may also reflect livestock removal, control of human infringement and climatic change. The quality of standing water may also be suspect, with inappropriate chemistry (eg hydrogen sulphide and high alkalinity) and biological characteristics (eg toxic algal blooms and pathogens).
BOWERS, J. E. AND R. M. TURNER. (U. S. Geological Survey, Tucson, AZ 85745). Dieback and episodic mortality of Cercidium microphyllum (foothill paloverde), a dominant Sonoran Desert tree. J. Torrey Bet, Sec. 128:000-000. 2001. - Past and current dieback of Cercidium microphyllum a dominant, drought-deciduous tree in the Sonoran Desert, was investigated at Tumamoc Hill. Tucson, Arizona, USA. Logistic regression predicted that the odds of a Ceracidium plant being alive should decrease with increasing circumference, association with the columnar cactus Carnegiea gigantea, and occurrence on steep slopes. Slope azimuth. parasitization by Phoradendron californicum, and distance to nearest Ceracidium within 5 m did not significantly affect the odds of survival. Ceracidium was a source of background mortality rather than a primary cause of dieback. Of the >1,000 living and dead plants sampled, 7.7% had died within the past 5 to 7 years. An additional 12.8% died in the more distant past. Diebacks tended to occur during severe deficits in annual, especially summer, min. More than half of the dead plants in the sample were greater than or equal to 50 cm in girth. In current and past diebacks on Tumamoc Hill, it seems likely that severe drought interacted with natural senescence of an aging population. weakening large, old trees and hastening their deaths.
European Starlings (Sturnus vulgaris) have recently invaded Arizona and breed in some areas but not in similar areas nearby. In Arizona, European Starlings commonly nest in cavities in saguaro cacti (Carnegiea gigantea) but do not excavate these cavities. To examine whether European Starlings compete with native woodpeckers for nest cavities in saguaros, we studied Gila Woodpeckers (Melanerpes uropygialis) and Northern Flickers (Colaptes auratus) in areas with European Starlings and in similar, nearby areas with no European Starlings. We determined which factors explained the variation in the number of nests of each species present on fifteen 10-ha plots. We also compared the location and dimensions of nest cavities used by each species to determine whether European Starlings use Gila Woodpecker nest cavities, Northern Flicker nest cavities, or both. We found that European Starlings compete with Gila Woodpeckers but not with Northern Flickers. This competition decreases the number of Gila Woodpeckers that nest in areas where European Starlings nest. European Starlings used Gila Woodpecker nest cavities, and there was a negative relationship between the number of European Starling nests and the number of Gila woodpecker nests that explained 46.7% of the variation in the number of Gila Woodpecker nests on the plots. European Starlings did not use Northern Flicker nest cavities, and we found no relationship between the number of European Starling nests and the number of Northern Flicker nests. In addition, the number of Gila Woodpecker nests was positively related to the number of large saguaros and negatively related to the slope of the plot. The number of Northern Flicker nests was positively related to the volume of ironwood (Olneya tesota). The number of European Starling nests was negatively related to the distance to agriculture and large lawns.
We describe the diet of desert bighorn sheep (Ovis canadensis mexicana) in the Sonoran Desert, western Arizona, from collections of fecal pellets and direct observations from March 1982 through December 1983. Bighorn sheep ate 121 plant taxa. Both sexes used a similar mean number of taxa each season, but not the same set of taxa. The similarity between male and female diets for any given season and area was variable (47-80%). Lamb diets were more similar to female diets than to male diets in spring. Sheep ate browse, forbs, and grass (x̄ = 64, 23, and 13%, respectively). The most important plants in the diet were propeller bush (Janusia gracilis), silverbush (Argythamnia lanceolata), desert mallow (Sphaeralcea ambigua), desert lavender (Hyptis emoryi), and white ratany (Krameria grayi). The use of a diverse and variable set of forages by desert bighorn sheep in western Arizona appears to be dictated by the availability and quality of plants that are determined by the unpredictable climate of the Sonoran Desert.