Desert Bighorn Research Articles

Predicting diet quality and genetic diversity of a desert-adapted ungulate with NDVI

Diet quality influences ungulate population dynamics but is difficult to measure at fine temporal or spatial resolution using field-intensive methods such as fecal nitrogen (FN). Increasingly, the remotely sensed vegetation index NDVI is used to represent potential ungulate diet quality, but NDVI's relationship with diet quality has yet to be examined for herbivores in desert environments. We evaluated how strongly NDVI was associated with diet quality of desert bighorn sheep (Ovis canadensis nelsoni) in the Mojave Desert using FN data from multiple years and populations. We considered effects of temporal resolution, geographic variability, and NDVI spatial summary statistic on the NDVI-diet quality relationship. NDVI was more reliably associated with diet quality over the entire growing season than with instantaneous diet quality for a population. NDVI was also positively associated with population genetic diversity, a proxy for long-term, population-level effects of diet quality. We conclude that NDVI is a useful diet quality indicator for Mojave Desert bighorn sheep and potentially other desert ungulates. However, it may not reliably track diet quality if NDVI data are too spatially coarse to detect microhabitats providing high-quality forage, or if diet is strongly influenced by forage items that are weakly correlated with landscape greenness.

Sympatric cattle grazing and desert bighorn sheep foraging

ABSTRACTForaging behavior affects animal fitness and is largely dictated by the resources available to an animal. Understanding factors that affect forage resources is important for conservation and management of wildlife. Cattle sympatry is proposed to limit desert bighorn population performance, but few studies have quantified the effect of cattle foraging on bighorn forage resources or foraging behavior by desert bighorn. We estimated forage biomass for desert bighorn sheep in 2 mountain ranges: the cattle‐grazed Caballo Mountains and the ungrazed San Andres Mountains, New Mexico. We recorded foraging bout efficiency of adult females by recording feeding time/step while foraging, and activity budgets of 3 age‐sex classes (i.e., adult males, adult females, yearlings). We also estimated forage biomass at sites where bighorn were observed foraging. We expected lower forage biomass in the cattle‐grazed Caballo range than in the ungrazed San Andres range and lower biomass at cattle‐accessible versus inaccessible areas within the Caballo range. We predicted bighorn would be less efficient foragers in the Caballo range. Groundcover forage biomass was low in both ranges throughout the study (Jun 2012–Nov 2013). Browse biomass, however, was 4.7 times lower in the Caballo range versus the San Andres range. Bighorn in the Caballo range exhibited greater overall daily travel time, presumably to locate areas of higher forage abundance. By selecting areas with greater forage abundance, adult females in the Caballo range exhibited foraging bout efficiency similar to their San Andres counterparts but lower overall daily browsing time. We did not find a significant reduction in forage biomass at cattle‐accessible areas in the Caballo range. Only the most rugged areas in the Caballo range had abundant forage, potentially a result of intensive historical livestock use in less rugged areas. Forage conditions in the Caballo range apparently force bighorn to increase foraging effort by feeding only in areas where adequate forage remains. © 2015 The Wildlife Society.

Genetic population structure of Peninsular bighorn sheep (Ovis canadensis nelsoni) indicates substantial gene flow across US–Mexico border

Within the United States (US), Peninsular bighorn sheep (Ovis canadensis nelsoni, PBS) are listed as federally endangered. Despite known metapopulation structure, little is known regarding functional connectivity across the international border with Mexico. Increasing threats to connectivity associated with highway expansion, renewable energy development, and completion of the US–Mexico border fence, led us to conduct a study of genetic variation and spatial structure. Blood and fecal samples were collected (n=224) on both sides of the border from 1992 to 2013. Genetic data was obtained for 25 microsatellite loci and 515 base pairs of the mitochondrial DNA control region. Microsatellite diversity (observed heterozygosity=0.56; allelic richness=4.1; inbreeding coefficient=0.01) was substantial despite past demographic declines. STRUCTURE analysis indicated the presence of three genetic populations, one of which spanned the international border. This pattern of genetic structure was supported by analysis of molecular variance for both microsatellites and mitochondrial DNA (P<0.01), and low-moderate pairwise fixation indices (FST=0.09–0.15; ΦST=0.18–0.27) indicated substantial gene flow among populations. Migrant detection tests indicated natal dispersal occurred within both sexes, with no evidence of sex bias. Despite the severe reductions in population abundance which led to federal listing in the US, these data suggest PBS have retained substantial genetic variation and show little evidence of a recent genetic bottleneck. Patterns of genetic spatial structure indicate gene flow throughout the ranges is common, and construction of a US–Mexico border fence or wind energy infrastructure would disrupt connectivity of the metapopulation. Future conservation efforts should focus on identifying dispersal corridors and maintaining functional connectivity to facilitate recolonization of unoccupied habitat.

Landscape models of space use by desert bighorn sheep in the Sonoran Desert of southwestern Arizona

The desert bighorn sheep (Ovis canadensis mexicana) is one of the few ungulates native to North America capable of surviving in harsh desert environments and xeric conditions. However, the effects of an increasingly arid climate on this species and its habitat are unknown. We sought to identify important predictors of desert bighorn sheep diurnal space use to provide new insight into management and conservation opportunities. We evaluated home range size and relative intensity of space use for 41 collared individuals monitored between 2007 and 2010 across a 14,217-km2 extent of Arizona's Sonoran Desert, including the Kofa National Wildlife Refuge and the United States Army Yuma Proving Ground. Using linear mixed models and an information-theoretic approach, we developed seasonal models of intensity of space use for the summer (Jun–Aug) and non-summer (Sep–May) seasons. Models included environmental variables representing escape terrain and distance from developed waters, and Normalized Difference Vegetation Index metrics that represented forage and preformed water resources. We found intensity of space use to be greater for females (than for males) in the summer season and smaller home range sizes for both sexes in the summer season. Escape terrain was the dominant predictor of intensity of space use in both seasons, but forage and preformed water resources were strong predictors only in the non-summer season. These results likely reflected a seasonal trade-off between escape terrain (i.e., predator avoidance) and limited forage and water resources, particularly for more risk-averse females. Effective conservation and management strategies for desert bighorn sheep should consider the availability of both quality forage and water resources in areas of escape terrain. Although more research is needed on species-specific vulnerabilities to climate change and drought, our approach to integrating vegetation indices into estimates of space use is highly transferable to analyses of other wide-ranging species occupying dynamic arid environments. © 2014 The Wildlife Society.

Estimation of regional sheep abundance based on group sizes

ABSTRACTWe used sightability models with aerial counts to estimate regional abundance of desert bighorn sheep (Ovis canadensis) in southwestern Arizona during 1992–2012. Because of incomplete spatial and temporal coverage of surveys, we integrated sightability estimates using Bayesian state‐space models. Although some game management units (GMUs) exhibited negative average growth rates during this period, temporal variability in growth was large. The combination of temporal variability and statistical uncertainty in the sightability estimates led to the selection of a regional model having zero mean growth from initial abundance. Hence, the model indicated a relatively stable population of desert bighorn sheep in southern Arizona, beginning with approximately 2,900 bighorn sheep in 1992 to the current number of approximately 2,300 sheep (2012). Our method provides statistically valid estimates of overall regional abundance not otherwise possible given the incomplete spatial coverage of surveys. Additionally, results have implications for other studies, common in wildlife management, where managers seek to integrate information across surveys with partial time‐series. © 2014 The Wildlife Society.

Use of agave by desert bighorn sheep

Abstract We hypothesized that, if agave (Agave) were used by desert ungulates as a source of moisture, they would be used more during drought than during periods with average or above-average rainfall. From 2004–2012, we counted the number of stalks of agave used by Nelson's bighorn sheep (Ovis canadensis nelsoni) in 10.3 ha in Deep Canyon, Santa Rosa Mountains, California. During years of average or above-average rainfall, bighorn sheep consumed <3% of available stalks of agave. During years with rainfall below average, bighorn sheep consumed from 20–53% of available stalks of agave, thus supporting our hypothesis.

Local extinction and unintentional rewilding of bighorn sheep (Ovis canadensis) on a desert island.

Bighorn sheep (Ovis canadensis) were not known to live on Tiburón Island, the largest island in the Gulf of California and Mexico, prior to the surprisingly successful introduction of 20 individuals as a conservation measure in 1975. Today, a stable island population of ∼500 sheep supports limited big game hunting and restocking of depleted areas on the Mexican mainland. We discovered fossil dung morphologically similar to that of bighorn sheep in a dung mat deposit from Mojet Cave, in the mountains of Tiburón Island. To determine the origin of this cave deposit we compared pellet shape to fecal pellets of other large mammals, and extracted DNA to sequence mitochondrial DNA fragments at the 12S ribosomal RNA and control regions. The fossil dung was 14C-dated to 1476–1632 calendar years before present and was confirmed as bighorn sheep by morphological and ancient DNA (aDNA) analysis. 12S sequences closely or exactly matched known bighorn sheep sequences; control region sequences exactly matched a haplotype described in desert bighorn sheep populations in southwest Arizona and southern California and showed subtle differentiation from the extant Tiburón population. Native desert bighorn sheep previously colonized this land-bridge island, most likely during the Pleistocene, when lower sea levels connected Tiburón to the mainland. They were extirpated sometime in the last ∼1500 years, probably due to inherent dynamics of isolated populations, prolonged drought, and (or) human overkill. The reintroduced population is vulnerable to similar extinction risks. The discovery presented here refutes conventional wisdom that bighorn sheep are not native to Tiburón Island, and establishes its recent introduction as an example of unintentional rewilding, defined here as the introduction of a species without knowledge that it was once native and has since gone locally extinct.

Using network theory to prioritize management in a desert bighorn sheep metapopulation

Connectivity models using empirically-derived landscape resistance maps can predict potential linkages among fragmented animal and plant populations. However, such models have rarely been used to guide systematic decision-making, such as identifying the most important habitat patches and dispersal corridors to protect or restore in order to maximize regional connectivity. Combining resistance models with network theory offers one means of prioritizing management for connectivity, and we applied this approach to a metapopulation of desert bighorn sheep (Ovis canadensis nelsoni) in the Mojave Desert of the southwestern United States. We used a genetic-based landscape resistance model to construct network models of genetic connectivity (potential for gene flow) and demographic connectivity (potential for colonization of empty habitat patches), which may differ because of sex-biased dispersal in bighorn sheep. We identified high-priority habitat patches and corridors and found that the type of connectivity and the network metric used to quantify connectivity had substantial effects on prioritization results, although some features ranked highly across all combinations. Rankings were also sensitive to our empirically-derived estimates of maximum effective dispersal distance, highlighting the importance of this often-ignored parameter. Patch-based analogs of our network metrics predicted both neutral and mitochondrial genetic diversity of 25 populations within the study area. This study demonstrates that network theory can enhance the utility of landscape resistance models as tools for conservation, but it is critical to consider the implications of sex-biased dispersal, the biological relevance of network metrics, and the uncertainty associated with dispersal range and behavior when using this approach.

Desert Bighorn Sheep: Changes in Genetic Variation Over Time and the Impact of Merging Populations

Abstract Founder effects, genetic bottlenecks, and genetic drift in general can lead to low levels of genetic diversity, which can influence the persistence of populations. We examine genetic variation in two populations of desert bighorn sheep Ovis canadensis from New Mexico and Mexico to measure change over time and evaluate the impact of introducing individuals from one population into the other. Over about three generations, the amount of genetic variation in the New Mexico population increased. In contrast, over about two generations the amount of genetic variation in the Mexican population decreased by a great extent compared with an estimate from another Mexican population from which it is primarily descended. The potential reasons for these changes are discussed. In addition, although both populations have low genetic variation, introduction of Mexican rams into the New Mexico population might increase the amount of genetic variation in the New Mexico population. Overall, it appears that management to increase genetic variation might require substantial detailed monitoring and evaluation of ancestry from the different sources and fitness components.

Detecting short-term responses to weekend recreation activity: Desert bighorn sheep avoidance of hiking trails

To study potential effects of recreation activity on habitat use of desert bighorn sheep (Ovis canadensis nelsoni), we placed Global Positioning System collars on 10 female bighorn sheep within the Wonderland of Rocks–Queen Mountain region of Joshua Tree National Park (JOTR), California, USA, from 2002 to 2004. Recreation use was highest from March to April and during weekends throughout the year. Daily use of recreation trails was highest during midday. By comparing habitat use (slope, ruggedness, distance to water, and distance to recreation trails) of female bighorn sheep on weekdays versus weekends, we were able to detect short-term shifts in behavior in response to recreation. In a logistic regression of bighorn sheep locations versus random locations for March and April, female locations at midday (1200 hours) were significantly more distant from recreation trails on weekends compared with weekdays. Our results indicate that within this region of JOTR, moderate to high levels of human recreation activity may temporarily exclude bighorn females from their preferred habitat. However, the relative proximity of females to recreation trails during the weekdays before and after such habitat shifts indicates that these anthropogenic impacts were short-lived. Our results have implications for management of wildlife on public lands where the co-existence of wildlife and recreational use is a major goal. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Conservation genetics and the persistence and translocation of small populations: bighorn sheep populations as examples

Understanding and evaluating the factors that influence the persistence of small populations and establishment of new populations are basic goals of conservation biology. Genetic effects due to genetic drift and inbreeding can have important impacts on the success of new populations. Many bighorn sheep populations in western North America have had low numbers and many have gone extinct. Here, the possible effects of genetic drift and inbreeding are evaluated in three populations of desert bighorn sheep initiated in the 1970s from translocations. One of these has no molecular genetic data but has substantial demographic data (Aravaipa Canyon), one has both extensive demographic data and some molecular genetic data (Red Rock), and one has limited demographic data and some molecular genetic data (Tiburon Island). Overall, either from theoretical pedigree analysis and population genetic estimates from demographic history (Aravaipa, Tiburon) or from molecular data (Red Rock, Tiburon), it appears that the levels of genetic drift and inbreeding are substantial in all of these populations. This impact was larger when higher variance in male reproductive success was assumed. In other words, it appears that genetic factors are and will be important in the establishment and persistence of these populations. These examples in long-term monitored bighorn sheep populations are relevant to many endangered species in similar situations where demographic data are available but there is little or no historical molecular genetic data.

Assessing the feasibility for reintroducing desert bighorn sheep to Guadalupe Mountains National Park: Habitat, migration corridors and challenges

Desert bighorn sheep were once part of the Guadalupe Mountains ecosystem but were extirpated in the 1930s due to disease transmittance from domestic sheep and goats, habitat loss, and unregulated hunting. The Guadalupe Mountains (Texas) are now managed by the National Parks Service which wishes to restore native species to their historical range. A habitat suitability study is an important step in restoring desert bighorn sheep to the mountains since restoration efforts are labor intensive and costly. This study uses Geographic Information System (GIS) modeling to identify suitable areas within the park for bighorn sheep and evaluate possible migration corridors between the park and a nearby mountain range (Sierra Diablo) that currently supports more than 400 bighorn sheep. Landscape analysis was conducted to compare the spatial attributes of the habitat areas in the Guadalupe Mountains to those in the Sierra Diablo Mountain Range and assess habitat quality. Our results found 79.95km2 of suitable habitat for desert bighorn sheep in Guadalupe Mountains National Park which exceeds the established size to support a minimum viable population size of bighorn sheep (100–125 individuals). Landscape analysis indicated a larger area of optimal habitat at the park with larger mean patch size, lower edge density, and shorter mean nearest neighbor distance than in the Sierra Diablo mountain range. The Sierra Diablo was found to have a larger area of suitable habitat which may indicate that the park may be able to support a smaller population if water development mirrors that of the Sierra Diablo. Several migration corridors were identified between the park and areas with a viable population of bighorn sheep and this connectivity is important for migration and gene flow. Considerations should be given to water development, non-native, competitor species (Barbary sheep) and predators (mountain lions).

Simulated Effects of Two Fire Regimes on Bighorn Sheep: The San Gabriel Mountains, California, USA

AbstractAn isolated population of bighorn sheep (Ovis canadensis nelsoni) occupies fire-adapted chaparral ranges in the San Gabriel Mountains, California, USA. During 1976 to 2006, the amount of high-suitability habitat on bighorn sheep winter-spring ranges resulting from fires (HSF) ranged from 670 ha to 3392 ha, and population estimates for sheep, which were correlated with HSF, ranged from 130 to 740 individuals. During the past 100 years, the majority of changes in the HSF were associated with a fire regime dominated by periodic large, wind-driven, high-intensity crown fires, which resulted in high variability in the HSF. Prior to European settlement, the fire regime likely included smaller, variable intensity fires that burned during summer, but that also would have influenced the HSF. The size of those smaller fires today is effectively constrained by current fire management strategies, including exclusion and suppression. We predicted that smaller summer fires would increase the amount of high-suitability habitat and reduce the variability observed in the HSF during contemporary times, and the outcomes of our comparisons were consistent with those predictions. Small fires can be implemented by prescription, and can help to stabilize and maintain a self-sustaining population of bighorn sheep in the San Gabriel Mountains.

Dispatches

Dispatches

Identification of novel variants of interferon-tau gene in Bighorn sheep (Ovis canadensis mexicana), Pelibuey sheep (Ovis aries) and its expression in hybrid blastocysts (Ovis canadensis × Ovis aries)

Palma-Irizarry, M., Damian-Matsumura, P., Betancourt, M., Romo, S., Perales, G., Lagunas-Martinez, A., Madrid-Marina, M. V., Mejia, O. and Ducolomb, Y. 2012. Identification of novel variants of interferon-tau gene in Bighorn sheep (Ovis canadensis mexicana), Pelibuey sheep (Ovis aries) and its expression in hybrid blastocysts (Ovis canadensis×Ovis aries). Can. J. Anim. Sci. 92: 275-283. The major signal for maternal recognition of pregnancy (MRP) in ruminants is interferon-tau (IFNT). Four novel sequences of the IFNT gene were isolated from genomic DNA obtained from blood samples of Bighorn, Pelibuey or the hybrid ewes. The deduced amino acid sequence of the hybrid ewe showed 100% identity with one Bighorn sheep IFNT sequence, suggesting that this sequence was inherited from Bighorn sheep. The high degree of identity between Pelibuey and Bighorn sheep sequences could be a possible explanation for the successful MRP in some Bighorn hybrid pregnancies. In vivo and in vitro domestic sheep (Ovis aries) and hy...

Identification of novel variants of interferon-tau gene in Bighorn sheep (Ovis canadensis mexicana), Pelibuey sheep (Ovis aries) and its expression in hybrid blastocysts (Ovis canadensis × Ovis aries)

Palma-Irizarry, M., Damian-Matsumura, P., Betancourt, M., Romo, S., Perales, G., Lagunas-Martínez, A., Madrid-Marina, M. V., Mejía, O. and Ducolomb, Y. 2012. Identification of novel variants of interferon-tau gene in Bighorn sheep ( Ovis canadensis mexicana ), Pelibuey sheep ( Ovis aries ) and its expression in hybrid blastocysts ( Ovis canadensis×Ovis aries ). Can. J. Anim. Sci. 92: 275–283. The major signal for maternal recognition of pregnancy (MRP) in ruminants is interferon-tau (IFNT). Four novel sequences of the IFNT gene were isolated from genomic DNA obtained from blood samples of Bighorn, Pelibuey or the hybrid ewes. The deduced amino acid sequence of the hybrid ewe showed 100% identity with one Bighorn sheep IFNT sequence, suggesting that this sequence was inherited from Bighorn sheep. The high degree of identity between Pelibuey and Bighorn sheep sequences could be a possible explanation for the successful MRP in some Bighorn hybrid pregnancies. In vivo and in vitro domestic sheep (Ovis aries) and hybrid sheep (Ovis aries×Ovis canadensis) blastocysts were obtained, and IFNT expression was measured by semiquantitative RT-PCR. In vivo and in vitro hybrid blastocysts showed lower expression of IFNT when compared with domestic blastocysts. In conclusion this study showed that there exists an effect of hybridization on IFNT expression and this can affect the MRP.

A comparison of Landsat TM and MODIS vegetation indices for estimating forage phenology in desert bighorn sheep (Ovis canadensis nelsoni) habitat in the Sonoran Desert, USA

Sonoran Desert bighorn sheep (Ovis canadensis mexicana) occupy rugged upland areas that experience irregular periods of vegetation growth associated with precipitation events. These episodic and often spatially limited events provide important forage and preformed water resources that may be important drivers of animal movement and habitat use. Habitat-use models that incorporate forage phenology would broaden our understanding of desert bighorn ecology and have considerable potential to inform conservation efforts for the species. Field-based methods are of limited utility to characterize vegetation phenology across large areas. Vegetation indices (VI) derived from satellite imagery are a viable alternative, but may be confounded by areas of high relief and shadow effects that can degrade VI values. The varying spatial and temporal resolutions of readily available satellite sensors, such as the Landsat thematic mapper (TM) and moderate-resolution imaging spectrometer (MODIS), present additional challenges. In this study, we sought to minimize degrading effects of terrain on TM- and MODIS-based estimates of vegetation phenology. We compared effects of high topographic relief on time series MODIS- and TM-based VI such as the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) using VI departures from average (DA) in shaded and unshaded areas. Sun elevation angle negatively impacted TM-derived NDVI and EVI values in areas of steep terrain. In contrast, MODIS-derived NDVI values were insensitive to sun elevation and terrain effects, whereas MODIS-derived EVI was degraded in areas of steep terrain. Time series MODIS NDVI and EVI DA values differed significantly during months of low sun elevation angle. Average MODIS EVI departure values were ≥20% lower than NDVI under these conditions, confounding time series estimates of plant phenology. Our best results were obtained from MODIS 16-day composited NDVI. These remote-sensing-based VI estimates of seasonal plant phenology and productivity can be used to inform models of habitat use and movements of desert bighorn over large areas.

Rapid Decrease in Horn Size of Bighorn Sheep: Environmental Decline, Inbreeding Depression, or Evolutionary Response to Trophy Hunting?

There are numerous examples demonstrating that selection has greatly influenced phenotypes in wild-harvested species. Here, a significant reduction in horn size in trophy desert bighorn sheep rams over 30 years in a reintroduced population in Aravaipa Canyon, Arizona is documented. After examining the potential effects of a detrimental change in the environment, inbreeding depression, and hunter-caused evolutionary change, it appears that environmental deterioration, apparently from the effects of drought, may be a major cause of the decline in horn size. In particular, the reduction in ram horn size is positively associated with reduced winter lifetime rainfall over the 3 decades. Over the same period, the demographic indicator lamb-to-ewe ratio has also declined in the Aravaipa population. On the other hand, lamb-to-ewe ratio has not declined statewide in Arizona, and the population size in Aravaipa appears to be increasing, suggesting local- and trait-specific effects. Using a theoretical context, neither inbreeding depression nor hunter selection by themselves appear to the sole causes of the lower horn size. However, some combination of environmental factors, inbreeding depression, and hunter selection may have caused the decrease in observed horn size. It is not clear what management actions might be successful in countering the environmental effects on horn size, but supplemental feeding and cattle removal are suggested while translocation is suggested to counter the effects of inbreeding depression and reduced hunting and translocation are suggested to counter the effects of hunter selection.

Genetic Analysis of Scats Reveals Minimum Number and Sex of Recently Documented Mountain Lions

Abstract Recent records of mountain lions Puma concolor and concurrent declines in desert bighorn sheep Ovis canadensis mexicana on Kofa National Wildlife Refuge in Arizona, United States, have prompted investigations to estimate the number of mountain lions occurring there. We performed noninvasive genetic analyses and identified species, individuals, and sex from scat samples collected from the Kofa and Castle Dome Mountains. From 105 scats collected, we identified a minimum of 11 individual mountain lions. These individuals consisted of six males, two females and three of unknown sex. Three of the 11 mountain lions were identified multiple times over the study period. These estimates supplement previously recorded information on mountain lions in an area where they were historically considered only transient. We demonstrate that noninvasive genetic techniques, especially when used in conjunction with camera-trap and radiocollaring methods, can provide additional and reliable information to wildlife managers, particularly on secretive species like the mountain lion.

Evaluation of Methods Used to Estimate Size of a Population of Desert Bighorn Sheep (Ovis canadensis mexicana) in New Mexico

Reliable estimates of size of populations are critical for successful management of translocated desert bighorn sheep (Ovis canadensis mexicana). As costs decrease and quality improves, remote cameras are increasingly used as a non-invasive tool to monitor populations of wildlife, but their efficacy has yet to be evaluated in a diversity of species and habitats. Here we investigate whether remote cameras, in combination with a simple mark-resight model, produce estimates of size of populations of desert bighorn sheep comparable to those derived from surveys conducted on the ground and using helicopters in the Fra Cristobal Range of south-central New Mexico. We determined that estimates of size of populations derived from remote cameras were comparable to those produced from direct observations obtained by surveys from helicopters and on the ground, that ca. 25 sequential samples of photographs produced comparable estimates of size of populations, but that photographs of single desert bighorn sheep dramatically lowered estimates of size of populations, and that placement of remote cameras on wildlife guzzlers in July produced the greatest number of photographs in the shortest time. Our results suggest that use of remote cameras may be an accurate, low-cost, and non-invasive means of estimating size of populations of desert bighorn sheep in New Mexico. Further research is warranted, ideally in tandem with ongoing surveys on the ground and using helicopters, in other management areas.