Desert Bighorn Research Articles

RECENT RECORDS OF DESERT BIGHORN SHEEP (OVIS CANADENSIS MEXICANA) IN EASTERN SONORA AND NORTHWESTERN CHIHUAHUA, MEXICO

The desert bighorn sheep (Ovis canadensis mexicana) was extirpated from most of its range in northern Mexico and the southwestern United States by the 1980s. Several populations have been established through reintroductions in both countries, but none in the Chihuahua–Sonora border region, where we report here 3 recent records. These records suggest the possibility of reintroducing bighorn sheep in northwestern Chihuahua and northeastern Sonora to increase the long-term viability of the species in the region.

Evaluation of Factors Potentially Influencing a Desert Bighorn Sheep Population

Abstract We studied a desert bighorn sheep (Ovis canadensis) population in the Mazatzal Mountains (primary study area) in central Arizona and population indices on reference areas between 1989 and 2003. We evaluated disease exposure and nutritional status of desert bighorn sheep, vegetation parameters, predator diets, and mountain lion (Puma concolor) harvest and abundance (1999–2003) and mountain lion predation (1995–2003) as factors potentially affecting desert bighorn sheep and population parameters. We measured rainfall monthly, monitored demography and relative abundance of desert bighorn sheep using aerial surveys, captured and placed radio collars on desert bighorn sheep, and collected samples of blood, parasites, and other pathogenic agents from captured animals. We measured mineral content, relative use, and structural composition of vegetation and determined diets of desert bighorn sheep adults and lambs, dietary intakes of nitrogen (FN), 2,6-diaminopimelic acid (FDAPA), neutral detergent fiber,...

HISTORICAL DISTRIBUTION OF DESERT BIGHORN SHEEP (OVIS CANADENSIS MEXICANA) IN COAHUILA, MEXICO

Abstract Historically, desert bighorn sheep occurred throughout Coahuila, Mexico, as far south as latitude 25°43′02″N. The subspecies Ovis canadensis mexicana probably was extirpated in Coahuila by 1970. We determined the historical range of desert bighorn sheep through a review of the available literature, interviews with long-term local residents, and a subjective habitat assessment. We found historical documentation of bighorn sheep in 14 mountain ranges (Sierra Alamitos, Sierra Maderas del Carmen, Sierra la Encantada, Sierra Hechiceros, Sierra del Pino, Sierra Mojada, Sierra el Rey, Sierra San Marcos y del Pino, Sierra Gavia, and Sierra la Paila), including 4 previously not recorded (Sierra el Fuste, Sierra el Almagre, Sierra de la Madera, and Sierra la Fragua). In addition, one archaeological site with remains of bighorn sheep was identified (La Candelaria Cave). The introduction of domestic livestock, particularly sheep and goats, and unregulated hunting probably were the major factors contributing ...

Grooming in desert bighorn sheep (Ovis canadensis mexicana) and the ghost of parasites past

Ectoparasites such as ticks have a negative effect on host fitness, whereas parasite-defense grooming is effective in removing ticks. The central control (programmed grooming) model proposes that animals engage in preventive tick-defense grooming in response to an internal timing mechanism, even in the absence of peripheral stimulation from parasites. This model predicts that smaller animals will groom more frequently than larger ones because of the higher cost of parasitism for a small animal (body size principle). The peripheral stimulation (stimulus driven) model predicts no size-related differences in grooming rate in the absence of tick bite irritation. We observed grooming behavior in a Chihuahuan desert population of bighorn sheep (Ovis canadensis mexicana), where ticks have been absent for perhaps thousands of years. Although not exposed to ticks, bighorns self groomed by means of oral and scratch grooming, albeit at very low rates compared to size-matched ungulates in both tick-infested and tick-free environments. Logistic regression and general linear models revealed both the probability that grooming was performed during a 10-min focal sample and the rate of grooming when it occurred was greater for younger, smaller age/sex categories of less body mass. Oral and scratch grooming were negatively associated with body mass during both years, with juveniles (X ¼ 15 kg) grooming the most frequently and the oldest males (X ¼ 70‐85 kg) grooming the least. Assuming that programmed grooming evolved in a tick-infested environment, the current grooming behavior of this population is a relict of their ancestral environment, an adaptation to the ‘‘ghost of parasites past.’’ Key words: body size principle, desert bighorn, grooming, programmed grooming model, ticks. [Behav Ecol]

WILDFIRE AND DESERT BIGHORN SHEEP HABITAT, SANTA CATALINA MOUNTAINS, ARIZONA

The desert bighorn sheep (Ovis canadensis mexicana) population in the Santa Catalina Mountains, Arizona, has declined since the 1920s and was virtually extirpated in the late 1990s. Urban development, human recreation, and changes in habitat conditions due to wildfire suppression have contributed to the decline. Wildfires in 2002 and 2003 burned approximately 46,701 ha in the Santa Catalina Mountains, including areas previously inhabited by desert bighorn sheep. Our objectives were to estimate the amount of potential and historical bighorn sheep habitat in the Santa Catalina Mountains and to determine if the fires improved habitat quality for bighorn sheep. We created a spatial habitat suitability model to estimate the amount of potential and historical habitat available for bighorn sheep in the Santa Catalina Mountains. We then used Burn Severity maps and the Normalized Difference Vegetation Index to examine the impact of recent wildfires on bighorn sheep habitat. We calculated 39,201 and 9,017 ha of potential and historical habitat of desert bighorn sheep, respectively. Historical bighorn sheep habitat in the western Santa Catalina Mountains declined 64% since 1989. Approximately 21% of potential habitat and 24% of historical bighorn sheep habitat were burned during the fires, most of which experienced low burn severity that was not high enough to remove vegetation that decreases habitat quality for desert bighorn sheep. Any consideration of translocation of desert bighorn sheep to the Santa Catalina Mountains should further assess the suitability of the areas identified as potential habitat.

Head to Head

In the absence of a reproducible validated critical-habitat delineation for Nelson's bighorn sheep (Ovis canadensis nelsoni) in the northern Santa Rosa Mountains, California, Turner et al. (2004) developed a quantitative habitat model based on biotic and a biotic habitat parameters comprised of the primary constituent elements allegedly used in the United States Fish and Wildlife Service's (USFWS) habitat model (USFWS 2000, 2001). Bighorn distribution and location (observation) data used by the USFWS in its model were 96% explained on the basis of the Turner et al. (2004) model; no validation or prediction could be made from the USFWS model (USFWS 2000, 2001). Criticisms by Ostermann et al. (2005) of the Turner et al. (2004) model emphasize a basic miscomprehension by Ostermann et al. (2005) of the differences between habitat characterization and habitat utilization. Most of the Ostermann et al. (2005) critique relates to data that were not provided to Turner et al. (2004). Failure of Ostermann et al. (2005) to fully grasp the sampling strategy used by Turner et al. (2004) relates to an incomplete comprehension of the statistical methodology employed rather than with the statistical procedures themselves. Claims by Ostermann et al. (2005) that Turner et al. (2004) made extrapolations to misdirect bighorn recovery efforts, drew inferences to other bighorn populations, alleged the northern population was normal, and equated sheep density (frequency of observation) to habitat quality are without substantiation, example, or merit. Contentions of problematic water source data are unsupported by the literature cited by Ostermann et al. (2005). The permissive attitude of resource agencies allowing management and conservation efforts to be directed by special interests largely in the absence of independent scientific scrutiny, casts a question of legitimacy over this Endangered Species Act listing, recovery strategy, and critical habitat delineation.

Head to Head

Turner et al. (2004) developed a habitat selection model for a population of desert bighorn sheep (Ovis canadensis) in the Peninsular Ranges of southern California that is listed as a threatened and endangered population by the state of California and the federal government, respectively. We are concerned that the recent publication of an article by Turner et al. (2004) could be detrimental to the management and recovery of bighorn sheep in the Peninsular Ranges because it lends credibility to a flawed analysis of bighorn sheep habitatuse patterns. The model attempts to extrapolate conclusions from a limited subset of bighorn sheep data that is not representative of the study area and was not gathered in a manner conducive to the analysis methods used by the authors. The authors classified habitat pixels as “active” or “inactive” based on the presence-absence of bighorn sheep observations without considering monitoring intensity. Turner et al. (2004) also failed to consider the implications of basing their model almost entirely on a bighorn sheep subpopulation known to have atypical habitat selection patterns. This subpopulation in the northwestern Santa Rosa Mountains frequently used food and water sources within hillside urban areas. Because the Turner et al. (2004) model was developed using data primarily from this atypical subpopulation, the model has low external validity and is unlikely to accurately predict habitat selection by other bighorn sheep subpopulations in the Peninsular Ranges. Furthermore, with the NW sub-population used in model development now excluded from urban areas, the Turner et al. (2004) model is unlikely to accurately predict habitat selection patterns of even this sub-population. We suggest the Turner et al. (2004) model is at best only applicable to this subpopulation between the years 1994–1998.

SAGUARO SPINE PENETRATED BIGHORN SHEEP SKULL

Animals that inhabit vegetative communities where thorns and spines are common should be capable of moving while avoiding injury from thorns and spines. On 21 December 2003, we found that a saguaro cactus (Carnegiea gigantea) spine had penetrated the lacrimal bone into the orbit of a desert bighorn sheep (Ovis canadensis) in south-central Arizona. The animal was observed with clinical infectious keratoconjunctivitis and was blind for 3 weeks prior to death. It is likely that the animal collided with a saguaro cactus after she became blinded by disease.

NEW RUMINANT HOSTS AND WIDER GEOGRAPHIC RANGE IDENTIFIED FOR BABESIA ODOCOILEI (EMERSON AND WRIGHT 1970)

Babesia odocoilei was found to infect two previously unknown host species, desert bighorn sheep (Ovis canadensis nelsoni) and musk oxen (Ovibos moschatus), both of which are members of the family Bovidae. Previously, B. odocoilei has been reported in only Cervidae hosts. New geographic regions where B. odocoilei infections have not been reported previously include Pennsylvania and New York, where fatal babesiosis has occurred in reindeer (Rangifer tarandus tarandus); New Hampshire, where elk (Cervus elaphus canadensis) have been affected; and California, home of the infected desert bighorn sheep. Infection with B. odocoilei in these hosts was confirmed by parasite small subunit ribosomal RNA gene sequence analysis. A serosurvey for B. odocoilei antibody activity in New Hampshire showed prevalence rates of 100% at two elk farms and 12% at another farm. Control of potential vector ticks, Ixodes scapularis, especially when translocating livestock, is imperative to prevent outbreaks of babesiosis in managed herds of potential host species.

Precipitation, density, and population dynamics of desert bighorn sheep on San Andres National Wildlife Refuge, New Mexico

Understanding the determinants of population size and performance for desert bighorn sheep (Ovis canadensis mexicana) is critical to develop effective recovery and manage- ment strategies. In arid environments, plant communities and consequently herbivore populations are strongly dependent upon precipitation, which is highly variable seasonal- ly and annually. We conducted a retrospective exploratory analysis of desert bighorn sheep population dynamics on San Andres National Wildlife Refuge (SANWR), New Mexico, 1941-1976, by modeling sheep population size as a function of previous popu- lation sizes and precipitation. Population size and trend of desert bighorn were best and well described (R2 = 0.89) by a model that included only total annual precipitation as a covariate. Models incorporating density-dependence, delayed density-dependence, and combinations of density and precipitation were less informative than the model contain- ing precipitation alone (AAICc=8.5-22.5). Lamb:female ratios were positively related to precipitation (current year: F134=7.09, P=0.012; previous year: F, 33=3.37, P=0.075)but were unrelated to population size (current year: F1 34=0.04, P=0.843; previous year: F| 33 =0.14, P=0.715). Instantaneous population rate of increase (r) was related to population size (F| 33 = 5.55; P=O.O25). Precipitation limited populations of desert bighorn sheep on SANWR primarily in a density-independent manner by affecting production or survival of lambs, likely through influences on forage quantity and quality. Habitat evaluations and recovery plans for desert bighorn sheep need to consider fundamental influences on desert bighorn populations such as precipitation and food, rather than focus solely on proximate issues such as security cover, predation, and disease. Moreover, the concept of carrying capacity for desert bighorn sheep may need re-evaluation in respect to highly variable (CV =35.6%) localized precipitation patterns. On SANWR carrying capacity for desert bighorn sheep was zero when total annual precipitation was <28.2 cm.

Highways block gene flow and cause a rapid decline in genetic diversity of desert bighorn sheep

AbstractThe rapid expansion of road networks has reduced connectivity among populations of flora and fauna. The resulting isolation is assumed to increase population extinction rates, in part because of the loss of genetic diversity. However, there are few cases where loss of genetic diversity has been linked directly to roads or other barriers. We analysed the effects of such barriers on connectivity and genetic diversity of 27 populations ofOvis canadensis nelsoni(desert bighorn sheep). We used partial Mantel tests, multiple linear regression and coalescent simulations to infer changes in gene flow and diversity of nuclear and mitochondrial DNA markers. Our findings link a rapid reduction in genetic diversity (up to 15%) to as few as 40 years of anthropogenic isolation. Interstate highways, canals and developed areas, where present, have apparently eliminated gene flow. These results suggest that anthropogenic barriers constitute a severe threat to the persistence of naturally fragmented populations.

A Wildlife Biologist with Skin Lesions

A 28-year-old, white, male wildlife biologist presented with multiple skin lesions on his left hand and forearm. These lesions varied in size from that of a penny to that of a quarter (i.e., 1020 mm). The patient had been working with Desert Bighorn Sheep, Ovis canadensis, in the Silver Bell Mountains of Pima County, Arizona. He physically subdued these sheep by hand. Before doing this, he would spray his flight suit, hands, gloves, and other equipment with chlorhexidine. Six weeks after starting this job in January 2004, he developed multiple raised, noner-~~~~~/-

A Wildlife Biologist with Skin Lesions

A 28-year-old, white, male wildlife biologist presented with multiple skin lesions on his left hand and forearm. These lesions varied in size from that of a penny to that of a quarter (i.e., 1020 mm). The patient had been working with Desert Bighorn Sheep, Ovis canadensis, in the Silver Bell Mountains of Pima County, Arizona. He physically subdued these sheep by hand. Before doing this, he would spray his flight suit, hands, gloves, and other equipment with chlorhexidine. Six weeks after starting this job in January 2004, he developed multiple raised, noner-~~~~~/-

THE RISE AND FALL OF PSOROPTIC SCABIES IN BIGHORN SHEEP IN THE SAN ANDRES MOUNTAINS, NEW MEXICO

Between 1978 and 1997, a combination of psoroptic scabies (Psoroptes spp.), mountain lion (Puma concolor) predation, and periodic drought reduced a population of native desert bighorn sheep (Ovis canadensis) in the San Andres Mountains (SAM), New Mexico, from >200 individuals to a single ewe. In 1999, this ewe was captured, ensured to be Psoroptes-free, and released back into the SAM. Eleven radio-collared rams were translocated from the Red Rock Wildlife Area (RRWA) in New Mexico into the SAM range and monitored through 2002 to determine whether Psoroptes spp. mites were still in the environment. None of these sentinel rams acquired scabies during this period, and no additional native sheep were found to be present in the range. In 2002, 51 desert bighorn sheep were translocated into the SAM from the Kofa National Wildlife Refuge in Arizona (n = 20) and the RRWA in New Mexico (n = 31). Twenty-one bighorn sheep have died in the SAM since that time, but Psoroptes spp. mites have not been detected on any of these animals, nor have they been found on mule deer (Odocoileus hemionus) sampled since 2000. We conclude that psoroptic scabies is no longer present in the San Andres bighorn sheep population and that psoroptic scabies poses a minimal to nonexistent threat to the persistence of this population at this time.

Habitat use by desert bighorn sheep during lambing

Habitat used for predator escape may be a factor limiting restoration of desert bighorn sheep (Ovis canadensis mexicana) in small mountain ranges in New Mexico. Female bighorn sheep seek isolation in discrete areas for parturition. Although parturition sites are used only for <3 days they play an important role in neonate survival. We compared habitat characteristics at pre-parturition (n = 21), parturition (n = 38), random (n = 38), and post-parturition sites (n = 21). At each site we calculated distance to steep terrain, elevation, ruggedness, slope, and visibility. Parturition and post-parturition sites were higher in elevation and more rugged than sites used during pre-parturition. Post-parturition sites were closer to terrain with 100% slope than the pre-parturition or parturition sites. Post-parturition sites had higher visibility and steeper slopes than the pre-parturition sites. Parturition sites were steeper, higher in elevation, more rugged, and had lower visibility than the random sites. Fidelity to parturition sites was observed on 1 of 38 occasions. Because lambing sites are used for short periods they are poorly understood and often ignored by land managers. Additional research is recommended in other desert bighorn sheep populations to understand better and predict habitat use during the lambing period.

Habitat use by female desert bighorn sheep in the Fra Cristobal Mountains, New Mexico, USA

Mexican desert bighorn sheep (Ovis canadensis mexicana) populations have declined since the 1980s, and restoration efforts are necessary to establish viable populations. Mexican desert bighorn sheep were translocated to the Fra Cristobal Mountains of south-central New Mexico in 1995. We described seasonal habitats used by female desert bighorn sheep by comparing characteristics of radiolocations with random locations within their home range. We developed a geographic information system to derive aspect, distance to steep slopes, elevation, slope, substrate associations, terrain ruggedness, and visibility. We developed seasonal logistic regression models that incorporated distance to 60% slope patches, ruggedness, slope, substrate, and visibility. Habitat characteristics at bighorn sheep locations were similar among seasons. Bighorn sheep locations were on steeper and more rugged terrain, closer to topography with a 60% slope, and had lower visibility than random locations. Based on our description of habitat selection by sheep, managers in New Mexico may need to reassess the amount of escape habitat in restoration areas to prioritize translocations and plan to manage predators.

THE INFLUENCE OF MOUNTAIN LION PREDATION ON BIGHORN SHEEP TRANSLOCATIONS

Abstract We studied the effects of mountain lion (Puma concolor) predation on 2 translocated populations of bighorn sheep (Ovis canadensis) in New Mexico, USA. During 1993, 32 Rocky Mountain bighorn sheep (O. c. canadensis) were translocated to Wheeler Peak Wilderness Area in northern New Mexico, and during 1992–1993, 31 desert bighorn sheep (O. c. mexicana) were translocated to Sierra Ladron in central New Mexico. We monitored both populations from release through 2000 using fixed-wing aircraft and ground and/or helicopter surveys. We determined cause of mortality for radiomarked individuals (n = 26) and calculated survival rates, cause-specific mortality rates, exponential growth rates, and lamb:ewe ratios. The post-lambing population estimates in 2000 were 180 in Wheeler Peak and 21 in Sierra Ladron. Annual adult survival was higher (P < 0.005) in the Wheeler Peak population (0.955) than in the Sierra Ladron population (0.784). Annual lamb:ewe ratios also were higher (P < 0.001) in the Wheeler Peak pop...

VIGILANCE, PREDATION RISK, AND THE ALLEE EFFECT IN DESERT BIGHORN SHEEP

Knowledge of how predation risk affects population survivorship is important for understanding predator–prey relationships and designing effective conservation strategies. The Allee effect (inverse density dependence) can be generated when antipredator strategies become inefficient in small groups of prey, thus making the population more susceptible to catastrophic population collapse and extinction. Many populations of desert bighorn sheep (Ovis canadensis) are declining, and predation is, in many cases, a major mortality factor. We studied desert bighorns at the Red Rock Wildlife Area, New Mexico, USA, to assess predation risk in different group types (ram, ewe, mixed) and age–sex classes. Multiple regression analysis revealed that predation risk (as estimated by individual vigilance) increased with smaller group size and greater inter-individual distance for all bighorns, with groups of <5 individuals subject to the greatest risk. Although rugged terrain is thought to provide refuge from predators, habitat ruggedness did not influence vigilance. The biggest males in ram groups experienced the greatest predation risk in that they were in the smallest groups, were most likely to be solitary, and were spaced farther apart from conspecifics. Although big rams spent twice as much time vigilant as other age–sex classes, collective alertness was lowest for ram groups. The conclusion that big rams were most at risk from predation was partially supported by the recent predation history of the population and previous studies in which mountain lion (Felis concolor) kills were biased toward rams. We discuss the management implications of these results for small populations subject to Allee effects, including reintroduction and/or translocation practices and selective removal of problem predators. We suggest that the use of multivariate techniques to simultaneously explore the influence of multiple factors and the use of vigilance as a correlate of predation risk would be useful management tools for assessing seasonal and class-specific vulnerability to predation.

Determination of critical habitat for the endangered Nelson's bighorn sheep in southern California

The United States Fish and Wildlife Service's (USFWS) designation of critical habitat for the endangered Nelson's bighorn sheep (Ovis canadensis nelsoni) in the Peninsular Ranges of southern California has been controversial because of an absence of a quantitative, repeatable scientific approach to the designation of critical habitat. We used 12,411 locations of Nelson's bighorn sheep collected from 1984–1998 to evaluate habitat use within 398 km2 of the USFWS-designated critical habitat in the northern Santa Rosa Mountains, Riverside County, California. We developed a multiple logistic regression model to evaluate and predict the probability of bighorn use versus non-use of native landscapes. Habitat predictor variables included elevation, slope, ruggedness, slope aspect, proximity to water, and distance from minimum expanses of escape habitat. We used Earth Resources Data Analysis System Geographic Information System (ERDAS-GIS) software to view, retrieve, and format predictor values for input to the Statistical Analysis Systems (SAS) software. To adequately account for habitat landscape diversity, we carried out an unsupervised classification at the outset of data inquiry using a maximum-likelihood clustering scheme implemented in ERDAS. We used the strata resulting from the unsupervised classification in a stratified random sampling scheme to minimize data loads required for model development. Based on 5 predictor variables, the habitat model correctly classified >96% of observed bighorn sheep locations. Proximity to perennial water was the best predictor variable. Ninety-seven percent of the observations were within 3 km of perennial water. Exercising the model over the northern Santa Rosa Mountain study area provided probabilities of bighorn use at a 30 × 30-m2 pixel level. Within the 398 km2 of USFWS-designated critical habitat, only 34% had a graded probability of bighorn use to non-use ranging from ≥1:1 to 6,044:1. The remaining 66% of the study area had odds of having bighorn use <1:1 or it was more likely not to be used by bighorn sheep. The USFWS designation of critical habitat included areas (45 km2) of importance (2.5 to ≥40 observations per km2 per year) to Nelson's bighorn sheep and large landscapes (353 km2) that do not appear to be used (<1 observation per km2 per year).

Population dynamics of bighorn sheep in the San Gabriel Mountains, California, 1967–2002

We analyzed long-term population data for bighorn sheep (Ovis canadensis nelsoni) occupying the San Gabriel Mountains in southern California. From 1967–1972 an estimated 500 bighorn sheep occupied that range. During 1968–1975 wildfires burned over half the occupied winter–spring ranges. Wildfires increased carrying capacity, and the population grew to 665 animals in 1976. During 1976–1982 adult mortality was low and recruitment was dependent on annual forage production and weather conditions during lambing. Rate of change indicated the population would double every 44 years, and it was considered to be stable. As vegetation matured and carrying capacity declined, mortality of adults and lambs increased and the population halved approximately every 8 years to 501±30 bighorn sheep in 1989. During 1989–1995 adult mortality increased and rate of change indicated the population would halve approximately every 2.8 years. From 1995–2002 the population was stable at 90 animals. Increased recruitment and an inverse relationship between number of adult ewes and recruitment rates between 1985 and 2001 suggested that neither habitat suitability nor disease was causing the dramatic population decline observed after 1989. We hypothesize that because of a declining mule deer (Odocoileus hemionus californicus) population, mountain lions (Puma concolor cougar) began to prey more frequently on bighorn sheep, which led to a dramatic decline in the sheep population after 1989.