Desert Bighorn Research Articles

Waterhole detection using a vegetation index in desert bighorn sheep (Ovis canadensis cremnobates) habitat.

In arid ecosystems, desert bighorn sheep are dependent on natural waterholes, particularly in summer when forage is scarce and environmental temperatures are high. To detect waterholes in Sierra Santa Isabel, which is the largest area of desert bighorn sheep habitat in the state of Baja California, Mexico, we used the normalized difference vegetation index (NDVI) and normalized difference water index (NDWI) from Sentinel-2 satellite images. Waterhole detection was based on the premise that sites with greater water availability, where NDVI was higher, can be identified by their density of vegetation greenness. For the detected waterholes, we estimated the escape terrain (presence of cliffs or steep, rocky slopes) around each by the vector ruggedness measure to determine their potential use by desert bighorn sheep based on the animals’ presence as documented by camera traps. We detected 14 waterholes with the NDVI of which 11 were known by land owners and 3 were unrecorded. Desert bighorn were not detected in waterholes with high values of escape terrain, i.e., flat areas. Waterhole detection by NDVI is a simple method, and with the assistance and knowledge of the inhabitants of the Sierra, it was possible to confirm the presence each waterhole in the field.

Genetic assessment of a bighorn sheep population expansion in the Silver Bell Mountains, Arizona.

BackgroundThe isolated population of desert bighorn sheep in the Silver Bell Mountains of southern Arizona underwent an unprecedented expansion in merely four years. We hypothesized that immigration from neighboring bighorn sheep populations could have caused the increase in numbers as detected by Arizona Game and Fish Department annual aerial counts.MethodsWe applied a multilocus genetic approach using mitochondrial DNA and nuclear microsatellite markers for genetic analyses to find evidence of immigration. We sampled the Silver Bell Mountains bighorn sheep before (2003) and during (2015) the population expansion, and a small number of available samples from the Gila Mountains (southwestern Arizona) and the Morenci Mine (Rocky Mountain bighorn) in an attempt to identify the source of putative immigrants and, more importantly, to serve as comparisons for genetic diversity metrics.ResultsWe did not find evidence of substantial gene flow into the Silver Bell Mountains population. We did not detect any new mitochondrial haplotypes in the 2015 bighorn sheep samples. The microsatellite analyses detected only one new allele, in one individual from the 2015 population that was not detected in the 2003 samples. Overall, the genetic diversity of the Silver Bell Mountains population was lower than that seen in either the Gila population or the Morenci Mine population.DiscussionEven though the results of this study did not help elucidate the precise reason for the recent population expansion, continued monitoring and genetic sampling could provide more clarity on the genetic demographics of this population.

Survival and cause‐specific mortality of desert bighorn sheep lambs

ABSTRACTJuvenile recruitment in desert bighorn sheep (Ovis canadensis mexicana) is highly variable, yet the mechanisms influencing neonate survival are not well understood. Because few studies have equipped desert bighorn sheep lambs with telemetry collars, definitive data on cause‐specific mortality, and lamb survival estimates are lacking. Our objectives were to estimate lamb survival rates and determine cause‐specific mortality for desert bighorn sheep lambs during a period of mountain lion (Puma concolor) and coyote (Canis latrans) removal in southwestern New Mexico, USA. We captured pregnant adult females each fall and fitted them with a telemetry collar and a vaginal implant transmitter to aid with neonate captures. We captured and radio‐collared 12 desert bighorn sheep lambs in 2012 and 14 in 2013 within 48 hours of parturition in the Peloncillo Mountains, New Mexico. We estimated lamb survival to 6 months of age. Across both years there were 14 mortalities, 12 of which were due to predation. Mountain lions killed 5 lambs (2 in 2012 and 3 in 2013), coyotes killed 4 lambs (all in 2013), a gray fox (Urocyon cinereoargenteus) killed 1 lamb in 2012, and 2 lambs were killed by unknown predators in 2013. Staged‐based survival estimates indicated the highest mortality rates occurred in the first week post birth; 5 of 14 lamb mortalities occurred before 7 days of age. Lamb survival to 6 months was substantially lower in 2013 (0.20 ± 0.11 [SE]) than in 2012 (0.71 ± 0.14) with the differences in survival attributed to increased coyote predation in 2013. We did not detect differences in body mass at birth between years or differences in body mass, chest girth, or neck circumference at birth between lambs that were killed by predators and those that survived. Coyotes, mountain lions, and the gray fox killed lambs <8 weeks of age, but only mountain lions killed lambs >8 weeks old. Predator removals focused around the parturition period of desert bighorn sheep may be more likely to influence lamb survival rates than removals outside of the lambing season. © 2018 The Wildlife Society.

The genetic legacy of 50 years of desert bighorn sheep translocations.

Conservation biologists have increasingly used translocations to mitigate population declines and restore locally extirpated populations. Genetic data can guide the selection of source populations for translocations and help evaluate restoration success. Bighorn sheep (Ovis canadensis) are a managed big game species that suffered widespread population extirpations across western North America throughout the early 1900s. Subsequent translocation programs have successfully re‐established many formally extirpated bighorn herds, but most of these programs pre‐date genetically informed management practices. The state of Nevada presents a particularly well‐documented case of decline followed by restoration of extirpated herds. Desert bighorn sheep (O. c. nelsoni) populations declined to less than 3,000 individuals restricted to remnant herds in the Mojave Desert and a few locations in the Great Basin Desert. Beginning in 1968, the Nevada Department of Wildlife translocated ~2,000 individuals from remnant populations to restore previously extirpated areas, possibly establishing herds with mixed ancestries. Here, we examined genetic diversity and structure among remnant herds and the genetic consequences of translocation from these herds using a genotyping‐by‐sequencing approach to genotype 17,095 loci in 303 desert bighorn sheep. We found a signal of population genetic structure among remnant Mojave Desert populations, even across geographically proximate mountain ranges. Further, we found evidence of a genetically distinct, potential relict herd from a previously hypothesized Great Basin lineage of desert bighorn sheep. The genetic structure of source herds was clearly reflected in translocated populations. In most cases, herds retained genetic evidence of multiple translocation events and subsequent admixture when founded from multiple remnant source herds. Our results add to a growing literature on how population genomic data can be used to guide and monitor restoration programs.

Assessing changes in functional connectivity in a desert bighorn sheep metapopulation after two generations.

Determining how species move across complex and fragmented landscapes and interact with human-made barriers is a major research focus in conservation. Studies estimating functional connectivity from movement, dispersal or gene flow usually rely on a single study period and rarely consider variation over time. We contrasted genetic structure and gene flow across barriers for a metapopulation of desert bighorn sheep (Ovis canadensis nelsoni) using genotypes collected 2000-2003 and 2013-2015. Based on the recently observed but unexpected spread of a respiratory pathogen across an interstate highway previously identified as a barrier to gene flow, we hypothesized that bighorn sheep changed how they interacted with that barrier, and that shifts in metapopulation structure influenced gene flow, genetic diversity and connectivity. Population assignment tests, genetic structure and genetic recapture demonstrated that bighorn sheep crossed the interstate highway in at least one location in 2013-2015, sharply reducing genetic structure between two populations, but supported conclusions of an earlier study that such crossings were very infrequent or unknown in 2000-2003. A recently expanded population established new links and caused decreases in genetic structure among multiple populations. Genetic diversity showed only slight increases in populations linked by new connections. Genetic structure and assignments revealed other previously undetected changes in movements and distribution, but much was consistent. Thus, we observed changes in both structural and functional connectivity over just two generations, but only in specific locations. Movement patterns of species should be revisited periodically to enable informed management, particularly in dynamic and fragmented systems.

Evaluation of desert bighorn sheep abundance surveys, southwestern Arizona, USA

ABSTRACTDesigning wildlife surveys requires biologists to identify their objectives and the accuracy (i.e., bias and precision) required to inform them. In southwestern Arizona, USA, abundance estimates and trends for desert bighorn sheep (Ovis canadensis) rely on detection‐corrected aerial surveys (i.e., group‐size estimator) to inform harvest and assess management actions. The accuracy requirements and trend resolution remain undefined, rendering the surveys ability to address management needs uncertain. We used simulations based on historical surveys to optimize survey efficiency, estimate the accuracy of alternative sampling designs, and evaluate if the accuracy produced by this survey meets management needs. Simulations varied by the amount of area surveyed and temporal frequency. Given annual surveys, we examined trend detection with alternative significance levels (α spanning 0.05–0.30). Our simulations, which accepted the survey assumptions, identified many designs producing unbiased and precise estimates (CV <20%). Alternatives exist for optimizing this survey. For instance, surveying >70% of a Game Management Unit (GMU) provides similar precision to 100% coverage. Population declines ≥12%/year are detectable with annual surveys over a 10‐year period when α = 0.05. Setting α = 0.3 enables detecting declines ≥14%/year within 3 years. This survey assumes constant detection, calculated in 1 GMU 2 decades ago, and applied to 10 other GMUs since. We tested this assumption by estimating group‐size detection from field data in another GMU for 4 years. Bighorn sheep detection varied across GMUs and survey periods. Abundance estimates using the new detection rates were approximately 40% lower than current estimates. Our survey evaluation revealed that differences in abundance of approximately 50% are often not detectable, precision is insufficient to detect large trends in a timely manner (i.e., 40% decline in 7 years), and assuming a fixed detection process remains unfounded. Alternative sampling designs that estimate detectability concomitant with the survey, combined with targeted studies, would better inform management objectives for these desert bighorn sheep. Our assessment demonstrates the problems that occur when survey requirements are vague or mismatch survey design, and that monitoring designs incapable of capturing spatial and temporal variation in detectability will risk misrepresenting animals’ population sizes and trends. © 2018 The Wildlife Society.

130 In Vitro Production of Hybrid Desert Bighorn×Domestic Sheep Embryos Using Frozen–Thawed Epididymal Semen from a Hunter-Harvested Ram

Although considered a species of least concern by the International Union for Conservation of Nature red list, the Desert Bighorn sheep (Ovis canadensis nelsoni) is listed in Appendix II of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) in Mexico, due to population size and the lack of protected areas. Postmortem epididymal sperm collected from a hunter-harvested Desert Bighorn sheep ram in Mexico, with an unofficial Safari Club International score of 197 2/8 and an estimated 5.5 years old, were used to evaluate the in vitro production (IVP) of embryos using postmortem-collected ram sperm. Testicles with epididymides were placed in the refrigerator ~45 min after harvest. Sperm were extracted from each epididymis and assessed separately for total motility (TM), progressive motility (PM), and membrane integrity using a phase contrast microscope. The sperm suspension was obtained from the distal end of both epididymides and cryopreserved 12 h postmortem using triladyl with egg yolk. Membrane integrity and morphology were evaluated using Eosin-Nigrosin stain. Sperm DNA fragmentation was analysed using the Halomax kit (Halosperm SL, Madrid, Spain) with fluorescence microscopy. Centrifugation with density gradient PureSperm (Nidacon International, Mölndal, Sweden) was used to remove dead sperm and debris before IVF. Ovaries were collected from Domestic sheep (Ovis aries) at a local slaughterhouse. The maturation medium was TCM-199 with Earle’s salts and a modified Tris-buffered medium was used for fertilization. Frozen straws of sperm from the Desert Bighorn ram were thawed for 45 s at 37°C. Sperm were diluted with modified Tween medium B with milk powder (mTBM) to a final concentration of 5 × 106 cells mL−1. The gametes were co-incubated for 18 h under previously described conditions. The cumulus cells were mechanically removed from zygotes and grown using a co-culture with granulosa cells in sequential media SOF1-SOF2. With regard to sperm collection, epididymis 1 produced 29 straws of sperm (0.25 mL, 136 × 106 sperm mL−1) and epididymis 2 produced 32 straws of sperm (0.25 mL, 68 × 106 sperm mL−1). The sperm sample used for IVF had TM of 60% and PM of 30%. Live dead staining of fresh sperm showed 68% live (i.e. intact cell membranes) and 28% post-thaw. Regarding DNA integrity, only 2% of sperm had DNA fragmentation at 0 h. Of 15 Grade 1 oocytes used for IVF, 4 cleaved (27%), with 1 developing to blastocyst stage (25%). The results show that frozen–thawed epididymal sperm collected from a recently deceased Desert Bighorn ram can provide a valuable source of sperm for IVP of embryos. These results also provide new information on Desert Bighorn sheep reproductive parameters for use in health assessment, or reproduction and conservation management through gene banking and assisted reproductive techniques.

The Gordian knot of mountain lion predation and bighorn sheep

ABSTRACTThe objective of this review is to generate a synthesis of research conducted on predation of bighorn sheep (Ovis canadensis) and to suggest directions for future research relative to current knowledge gaps and a novel hypothesis. This review is primarily based on literature from the last 60 years on desert bighorn sheep (O. c. nelsoni), Rocky Mountain bighorn sheep (O. c. canadensis), and mountain lion (Puma concolor) predation. Although, many predators kill bighorn sheep, only mountain lions are currently considered to be the primary proximate cause of mortality for many bighorn sheep populations. The ultimate cause of this phenomenon has vexed wildlife managers for >40 years. There are 3 primary reasons for increased predation on bighorn sheep by mountain lions. First, there is an increased presence of mountain lions in habitats where they were historically absent or rare because of the expansion of mule deer (Odocoileus hemionus) following the extensive conversion of fire‐maintained grasslands to shrublands in the late‐1800s. Second, is the extirpation of the 2 dominant apex carnivores (wolves [Canis lupus] and grizzly bears [Ursus arctos]) during this same time period and a hypothesized numerical response of mountain lions to those extirpations. Finally, the response of mountain lions to the cessation of >70 years of intensive predator control has often resulted in unsustainable mountain lion‐bighorn sheep ratios, especially for desert bighorn sheep. Additionally, the effect of mountain lion predation is exacerbated by declines in bighorn sheep that do not result in declines in mountain lions because of their ability to prey switch to mule deer, elk (Cervus canadensis), or domestic cattle; kleptoparasitism of mountain lions kills, by ursids and canids, resulting in higher kill rates for mountain lions; and a possible ecological trap where adaptations derived over evolutionary time are no longer adaptive because of human‐induced changes in the sympatric apex predator guild. Control of mountain lions, when mountain lion‐ungulate ratios are high, might be required to protect small or endangered bighorn sheep populations, and to produce bighorn sheep for restoration efforts. © 2017 The Wildlife Society.

MOLECULAR SURVEILLANCE FOR BARTONELLA, BORRELIA, AND RICKETTSIA SPECIES IN TICKS FROM DESERT BIGHORN SHEEP ( OVIS CANADENSIS) AND MULE DEER ( ODOCOILEUS HEMIONUS) IN SOUTHERN CALIFORNIA, USA.

: Ticks (Acari: Ixodidae) were collected from 44 desert bighorn sheep ( Ovis canadensis) and 10 mule deer ( Odocoileus hemionus) in southern California, US during health inspections in 2015-16. Specimens were identified and screened by PCR analysis to determine the presence and prevalence of Bartonella, Borrelia, and Rickettsia species in ticks associated with these wild ruminants. None of the 60 Dermacentor hunteri and 15 Dermacentor albipictus ticks tested yielded positive PCR results. Additional tick specimens should be collected and tested to determine the prevalence of these confirmed or suspected tickborne pathogens within ruminant populations.

Efecto del uso de medio secuencial humano en la producción de blastocistos de hembra ovis canadensis mexicana por clonación manual

RESUMEN. Efecto del uso de medio secuencial humano en la producción de blastocistos de hembra Ovis canadensis mexicana por clonación manual interespecies. Desde el evidente problema del peligro de extinción que enfrenta un número significativo de especies silvestres a nivel mundial, se han aplicado biotecnologías encaminadas a promover su conservación y reproducción. Tal es el caso de la transferencia nuclear de células somáticas (TNCS) interespecies que ha sido aplicada y ha producido exitosamente embriones y crías nacidas vivas en algunas de estas especies. Sin embargo, la TNCS interespecies aún debe lidiar con otros problemas como la baja tasa de producción de embriones y de supervivencia de las crías nacidas (3-6%). Problemas que, entre otros, involucran la alta incidencia de fragmentación embrionaria. Los estudios son ahora dirigidos a resolver estos obstáculos, determinando el efecto de diferentes medios o suplementos utilizados en la producción in vitro de embriones. El objetivo de este estudio fue aplicar una variante de la TNCS interespecies (Clonación Manual-HMC) para la producción de embriones, determinando el efecto del uso de medios secuenciales humanos, en el borrego salvaje mexicano amenazado de extinción O. c. mexicana. Los resultados muestran que la producción de embriones incrementa con el uso de medios secuenciales humanos, permitiendo al embrión desarrollarse hasta la etapa de blastocisto (16% vs. 0%, P < 0.05). Este es el primer reporte de clonación exitosa de embriones de hembra O. c. mexicana en México.

Single-Species and Multiple-Species Connectivity Models for Large Mammals on the Navajo Nation

Abstract. Estimation of connectivity for multiple species could increase the efficiency of resource management and elucidate trade-offs among maintenance of connectivity for different taxa. We identified potential areas of high connectivity for 5 species of mammals on the Navajo Nation and adjacent lands in Utah, Arizona, and New Mexico, USA: mountain lion (Puma concolor), mule deer (Odocoileus hemionus), desert bighorn sheep (Ovis canadensis nelsoni), American black bear (Ursus americanus), and pronghorn (Antilocapra americana). These species were identified by the Navajo Nation as relevant to the benefit of their present and future generations. We used telemetry data to calculate utilization distributions, derive model permeability (the probability that a given location facilitates animal movement), and assess connectivity (the realization of permeability across a landscape) for desert bighorn sheep, black bear, and pronghorn. We based models of connectivity for mountain lion and mule deer on expert-ide...

Detection of bacterial-reactive natural IgM antibodies in desert bighorn sheep populations.

Ecoimmunology is a burgeoning field of ecology which studies immune responses in wildlife by utilizing general immune assays such as the detection of natural antibody. Unlike adaptive antibodies, natural antibodies are important in innate immune responses and often recognized conserved epitopes present in pathogens. Here, we describe a procedure for measuring natural antibodies reactive to bacterial antigens that may be applicable to a variety of organisms. IgM from desert bighorn sheep plasma samples was tested for reactivity to outer membrane proteins from Vibrio coralliilyticus, a marine bacterium to which sheep would have not been exposed. Immunoblotting demonstrated bighorn sheep IgM could bind to a variety of bacterial cell envelope proteins while ELISA analysis allowed for rapid determination of natural antibody levels in hundreds of individual animals. Natural antibody levels were correlated with the ability of plasma to kill laboratory strains of E. coli bacteria. Finally, we demonstrate that natural antibody levels varied in two distinct populations of desert bighorn sheep. These data demonstrate a novel and specific measure of natural antibody function and show that this varies in ecologically relevant ways.

Extreme precipitation variability, forage quality and large herbivore diet selection in arid environments

Nutritional ecology forms the interface between environmental variability and large herbivore behaviour, life history characteristics, and population dynamics. Forage conditions in arid and semi‐arid regions are driven by unpredictable spatial and temporal patterns in rainfall. Diet selection by herbivores should be directed towards overcoming the most pressing nutritional limitation (i.e. energy, protein [nitrogen, N], moisture) within the constraints imposed by temporal and spatial variability in forage conditions. We investigated the influence of precipitation‐induced shifts in forage nutritional quality and subsequent large herbivore responses across widely varying precipitation conditions in an arid environment. Specifically, we assessed seasonal changes in diet breadth and forage selection of adult female desert bighorn sheep Ovis canadensis mexicana in relation to potential nutritional limitations in forage N, moisture and energy content (as proxied by dry matter digestibility, DMD). Succulents were consistently high in moisture but low in N and grasses were low in N and moisture until the wet period. Nitrogen and moisture content of shrubs and forbs varied among seasons and climatic periods, whereas trees had consistently high N and moderate moisture levels. Shrubs, trees and succulents composed most of the seasonal sheep diets but had little variation in DMD. Across all seasons during drought and during summer with average precipitation, forages selected by sheep were higher in N and moisture than that of available forage. Differences in DMD between sheep diets and available forage were minor. Diet breadth was lowest during drought and increased with precipitation, reflecting a reliance on few key forage species during drought. Overall, forage selection was more strongly associated with N and moisture content than energy content. Our study demonstrates that unlike north‐temperate ungulates which are generally reported to be energy‐limited, N and moisture may be more nutritionally limiting for desert ungulates than digestible energy.

Simulating the spread of selection-driven genotypes using landscape resistance models for desert bighorn sheep.

Landscape genetic studies based on neutral genetic markers have contributed to our understanding of the influence of landscape composition and configuration on gene flow and genetic variation. However, the potential for species to adapt to changing landscapes will depend on how natural selection influences adaptive genetic variation. We demonstrate how landscape resistance models can be combined with genetic simulations incorporating natural selection to explore how the spread of adaptive variation is affected by landscape characteristics, using desert bighorn sheep (Ovis canadensis nelsoni) in three differing regions of the southwestern United States as an example. We conducted genetic sampling and least-cost path modeling to optimize landscape resistance models independently for each region, and then simulated the spread of an adaptive allele favored by selection across each region. Optimized landscape resistance models differed between regions with respect to landscape variables included and their relationships to resistance, but the slope of terrain and the presence of water barriers and major roads had the greatest impacts on gene flow. Genetic simulations showed that differences among landscapes strongly influenced spread of adaptive genetic variation, with faster spread (1) in landscapes with more continuously distributed habitat and (2) when a pre-existing allele (i.e., standing genetic variation) rather than a novel allele (i.e., mutation) served as the source of adaptive genetic variation. The combination of landscape resistance models and genetic simulations has broad conservation applications and can facilitate comparisons of adaptive potential within and between landscapes.

Variable terrestrial GPS telemetry detection rates: Addressing the probability of successful acquisitions

ABSTRACTStudies using global positioning system (GPS) telemetry rarely result in 100% fix success rates (FSR), which may bias datasets because data loss is systematic rather than a random process. Previous spatially explicit models developed to correct for sampling bias have been limited to small study areas, a small range of data loss, or were study‐area specific. We modeled environmental effects on FSR from desert to alpine biomes, investigated the full range of potential data loss (0–100% FSR), and evaluated whether animal body position can contribute to lower FSR because of changes in antenna orientation based on GPS detection rates for 4 focal species: cougars (Puma concolor), desert bighorn sheep (Ovis canadensis nelsoni), Rocky Mountain elk (Cervus elaphus nelsoni), and mule deer (Odocoileus hemionus). Terrain exposure and height of over story vegetation were the most influential factors affecting FSR. Model evaluation showed a strong correlation (0.88) between observed and predicted FSR and no significant differences between predicted and observed FSRs using 2 independent validation datasets. We found that cougars and canyon‐dwelling bighorn sheep may select for environmental features that influence their detectability by GPS technology, mule deer may select against these features, and elk appear to be nonselective. We observed temporal patterns in missed fixes only for cougars. We provide a model for cougars, predicting fix success by time of day that is likely due to circadian changes in collar orientation and selection of daybed sites. We also provide a model predicting the probability of GPS fix acquisitions given environmental conditions, which had a strong relationship (r2 = 0.82) with deployed collar FSRs across species. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Tolerance to Disturbance Regulated by Attractiveness of Resources: A Case Study of Desert Bighorn Sheep Within the River Mountains, Nevada

Abstract. Human activity may mimic predation risks for wildlife by causing abandonment of foraging sites and increasing expenditure of energy. Animals that can tolerate nonlethal disturbance may minimize these fitness costs. We examine this aspect of the risk—disturbance hypothesis by first analyzing recent habitat use of desert bighorn sheep relative to areas of attraction and disturbance. We then compare and contrast sheep responses to differing levels of anthropogenic disturbance between 2 time periods, 30 years apart. Desert bighorn sheep were tolerant of suburban activity when a consistent forage resource (municipal grass) was provided. Males were more tolerant than females, and females returned to natural, steep areas during the birthing season. Increased recreation activity, specifically mountain bike use, may have resulted in avoidance by sheep of otherwise suitable habitat that had been occupied decades earlier, thereby reducing availability of limited habitat. Tolerance increased only when attra...

Foraging at the wildland–urban interface decouples weather as a driver of recruitment for desert bighorn sheep

ABSTRACTA growing number of ungulate populations are living within or near the wildland–urban interface. When resources at the interface are of greater quality than that of adjacent natural habitat, wildlife can be attracted to these developed areas. Little is known about how use of the wildland–urban interface by wildlife may affect vital rates. Under natural conditions, recruitment by desert bighorn sheep (Ovis canadensis nelsoni) correlates with variation in the timing and amount of rainfall that initiates and enhances growth of annual plant species. However, for populations that forage in developed areas, this relationship may become decoupled. In the River Mountains of Nevada, USA, desert bighorn sheep have been feeding in a municipal park at the wildland–urban interface since its establishment in 1985. Approximately one‐third of the population now uses the park during summer months when nutritional content of natural forage is low. We hypothesized that use of this municipal area, with its abundant vegetation and water resources, may have decoupled the previous relationship between precipitation and lamb recruitment. We assessed variables known to affect lamb recruitment before (1971–1986) and after (1987–2006) establishment of the park using linear regression models. Our top candidate model for the pre‐park period indicated that total November precipitation was the greatest driver of lamb recruitment in this population. After park establishment, this relationship became decoupled because lamb recruitment was no longer driven by weather variables. These results raise questions about the effects of decoupling drivers of population growth and maintaining natural populations near urban areas. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Desert bighorn sheep lambing habitat: Parturition, nursery, and predation sites

ABSTRACTFitness of female ungulates is determined by neonate survival and lifetime reproductive success. Therefore, adult female ungulates should adopt behaviors and habitat selection patterns that enhance survival of neonates during parturition and lactation. Parturition site location may play an important role in neonatal mortality of desert bighorn sheep (Ovis canadensis mexicana) when lambs are especially vulnerable to predation, but parturition sites are rarely documented for this species. Our objectives were to assess environmental characteristics at desert bighorn parturition, lamb nursery, and predation sites and to assess differences in habitat characteristics between parturition sites and nursery group sites, and predation sites and nursery group sites. We used vaginal implant transmitters (VITs) to identify parturition sites and capture neonates. We then compared elevation, slope, terrain ruggedness, and visibility at parturition, nursery, and lamb predation sites with paired random sites and compared characteristics of parturition sites and lamb predation sites to those of nursery sites. When compared to random sites, odds of a site being a parturition site were highest at intermediate slopes and decreased with increasing female visibility. Odds of a site being a predation site increased with decreasing visibility. When compared to nursery group sites, odds of a site being a parturition site had a quadratic relationship with elevation and slope, with odds being highest at intermediate elevations and intermediate slopes. When we compared predation sites to nursery sites, odds of a site being a predation were highest at low elevation areas with high visibility and high elevation areas with low visibility likely because of differences in hunting strategies of coyote (Canis latrans) and puma (Puma concolor). Parturition sites were lower in elevation and slope than nursery sites. Understanding selection of parturition sites by adult females and how habitat characteristics at these sites differ from those at predation and nursery sites can provide insight into strategies employed by female desert bighorn sheep and other species during and after parturition to promote neonate survival. © 2016 The Wildlife Society.

Potential Foraging Decisions by a Desert Ungulate to Balance Water and Nutrient Intake in a Water-Stressed Environment.

Arid climates have unpredictable precipitation patterns, and wildlife managers often provide supplemental water to help desert ungulates endure the hottest, driest periods. When surface water is unavailable, the only source of water for ungulates comes from the forage they consume, and they must make resourceful foraging decisions to meet their requirements. We compared two desert bighorn sheep (Ovis canadensis nelsoni) populations in Arizona, USA: a treatment population with supplemental water removed during treatment, and a control population. We examined whether sheep altered their seasonal diets without supplemental water. We calculated water and nutrient intake and metabolic water production from dry matter intake and forage moisture and nitrogen content, to determine whether sheep could meet their seasonal daily water and nutrient requirements solely from forage. Diets of sheep were higher in protein (all seasons) and moisture (autumn and winter) during treatment compared to pretreatment. During treatment, sheep diet composition was similar between the treatment and control populations, which suggests, under the climatic conditions of this study, water removal did not influence sheep diets. We estimated that under drought conditions, without any surface water available (although small ephemeral potholes would contain water after rains), female and male sheep would be unable to meet their daily water requirements in all seasons, except winter, when reproductive females had a nitrogen deficit. We determined that sheep could achieve water and nutrient balances in all seasons by shifting their total diet proportions by 8–55% from lower to higher moisture and nitrogen forage species. We elucidate how seasonal forage quality and foraging decisions by desert ungulates allow them to cope with their xeric and uncertain environment, and suggest that, with the forage conditions observed in our study area during this study period, providing supplemental water during water-stressed periods may not be necessary for desert bighorn sheep.

Utilización de aguajes por el borrego cimarrón (Ovis canadensis cremnobates) y análisis de calidad del agua en Sierra Santa Isabel, Baja California, México

Water used by bighorn sheep during the 2011 and 2013 dry seasons and the rainy season and drought of 2015 in the Sierra Santa Isabel of the State of Baja California, Mexico was analyzed for seven physicochemical parameters. At four watering sites, 260 photographs of sheep were obtained. Females, yearlings, and lambs accounted for 73% of the photographs. In the rainy season at two watering sites, conductivity was 1.31 µS/cm2 and 1.92 µS/cm2 and total dissolved solids was 0.65 and 0.95 ppt, indicating low salt content and safe for bighorn sheep. The watering sites with greater use by bighorn sheep were El Zamora (n = 120) and El Cordero (n = 67), which also had the best water quality. The frequent use by females and yearlings of the two sites with optimal water quality support the belief that watering sites for lambing and recruitment of bighorn sheep is important.