Bighorn Sheep Ovis Canadensis Research Articles

Population connectivity patterns of genetic diversity, immune responses and exposure to infectious pneumonia in a metapopulation of desert bighorn sheep.

Habitat fragmentation is an important driver of biodiversity loss and can be remediated through management actions aimed at maintenance of natural connectivity in metapopulations. Connectivity may protect populations from infectious diseases by preserving immunogenetic diversity and disease resistance. However, connectivity could exacerbate the risk of infectious disease spread across vulnerable populations. We tracked the spread of a novel strain of Mycoplasma ovipneumoniae in a metapopulation of desert bighorn sheep Ovis canadensis nelsoni in the Mojave Desert to investigate how variation in connectivity among populations influenced disease outcomes. M. ovipneumoniae was detected throughout the metapopulation, indicating that the relative isolation of many of these populations did not protect them from pathogen invasion. However, we show that connectivity among bighorn sheep populations was correlated with higher immunogenetic diversity, a protective immune response and lower disease prevalence. Variation in protective immunity predicted infection risk in individual bighorn sheep and was associated with heterozygosity at genetic loci linked to adaptive and innate immune signalling. Together, these findings may indicate that population connectivity maintains immunogenetic diversity in bighorn sheep populations in this system and has direct effects on immune responses in individual bighorn sheep and their susceptibility to infection by a deadly pathogen. Our study suggests that the genetic benefits of population connectivity could outweigh the risk of infectious disease spread and supports conservation management that maintains natural connectivity in metapopulations.

Breeding migrations by bighorn sheep males are driven by mating opportunities.

In some species where male mating success largely depends on intrasexual competition, males can adopt migratory or resident strategies to seek breeding opportunities. The resulting mixture of resident and migrant tactics within a population can have important ecological, genetic, and evolutionary consequences for metapopulations. Bighorn sheep Ovis canadensis males establish a linear dominance hierarchy that influences their mating tactics. Some males perform breeding migrations during the pre‐rut and rut to seek mating opportunities, but little is known about these seasonal movements. We analyzed presence/absence data for 62 marked bighorn males during six mating seasons (20–32 males/year) in the Sheep River Provincial Park, Alberta, Canada, where hunting was not allowed. On average, about half of males left their natal population to rut elsewhere. The proportion of males leaving (yearly range 15%–69%) increased as the number of resident mature males increased and the populational sex ratio decreased, with fewer females during the pre‐rut. Among those leaving the park, 24% did so in October, while the trophy sheep hunting season was open. Detailed monitoring of breeding migrations in protected populations could inform management strategies to limit evolutionary impacts of hunting, which can alter size‐dependent mortality and create artificial pressures driving changes on heritable traits.

Modelling management strategies for chronic disease in wildlife: Predictions for the control of respiratory disease in bighorn sheep

Abstract Controlling persistent infectious disease in wildlife populations is an ongoing challenge for wildlife managers and conservationists worldwide, and chronic diseases in particular remain a pernicious problem. Here, we develop a dynamic pathogen transmission model capturing key features of Mycoplasma ovipneumoniae infection, a major cause of population declines in North American bighorn sheep Ovis canadensis. We explore the effects of model assumptions and parameter values on disease dynamics, including density‐ versus frequency‐dependent transmission, the inclusion of a carrier class versus a longer infectious period, host survival rates, disease‐induced mortality and recovery rates and the epidemic growth rate. Along the way, we estimate the basic reproductive ratio, R0, for M. ovipneumoniae in bighorn sheep to fall between approximately 1.36 and 1.74. We apply the model to compare efficacies across a suite of management actions following an epidemic, including test‐and‐remove, depopulation‐and‐reintroduction, range expansion, herd augmentation and density reduction. Our results suggest that test‐and‐remove, depopulation‐and‐reintroduction and range expansion could help persistently infected bighorn sheep herds recovery following an epidemic. By contrast, augmentation could lead to worse outcomes than those expected in the absence of management. Other management actions that improve host survival or reduce disease‐induced mortality are also likely to improve population size and persistence of chronically infected herds. Synthesis and applications. Dynamic transmission models like the one employed here offer a structured, logical approach for exploring hypotheses, planning field experiments and designing adaptive management. We find that management strategies that removed infected animals or isolated them within a structured metapopulation were most successful at facilitating herd recovery from a low‐prevalence, chronic pathogen. Ideally, models like ours should operate iteratively with field experiments to triangulate on better approaches for managing wildlife diseases.

ROAD AND RAIL FATALITIES OF ELK, BIGHORN SHEEP, AND GRAY WOLVES IN JASPER NATIONAL PARK, ALBERTA, 1980–2018

Established in 1907, Jasper National Park (JNP) comprises 10,880 km2 of mountainous terrain in western Alberta, Canada. Its large mammals have been protected from hunting and trapping, but are subject to accidental collisions with vehicles and trains on the Yellowhead Highway and the Canadian National Railway (CNR) that transect JNP. This paper reviews the park's historical inventory of Elk (Cervus elaphus), Bighorn Sheep (Ovis Canadensis), and Gray Wolves (Canis lupus), and reports on their number killed by vehicles and trains from 1980 to 2018. Elk population estimates declined from 1000 in 1975 to 318 in 2018. An aerial survey of Bighorn Sheep flown in 2018 over all of JNPs sheep range recorded a decline of 58–62% compared to 1987. In the lower main valley, discrete bands of rams and ewes declined on 2 traditional winter ranges. The road and rail fatalities of Elk and sheep were superimposed on predation. In the late 1970s, wolves were estimated at 160, but reached an undetermined low in 2018 following year-round trapping on JNPs boundaries and accidental fatalities on the park's roads and railways.

How sure are you? A web-based application to confront imperfect detection of respiratory pathogens in bighorn sheep.

The relationships between host-pathogen population dynamics in wildlife are poorly understood. An impediment to progress in understanding these relationships is imperfect detection of diagnostic tests used to detect pathogens. If ignored, imperfect detection precludes accurate assessment of pathogen presence and prevalence, foundational parameters for deciphering host-pathogen dynamics and disease etiology. Respiratory disease in bighorn sheep (Ovis canadensis) is a significant impediment to their conservation and restoration, and effective management requires a better understanding of the structure of the pathogen communities. Our primary objective was to develop an easy-to-use and accessible web-based Shiny application that estimates the probability (with associated uncertainty) that a respiratory pathogen is present in a herd and its prevalence given imperfect detection. Our application combines the best-available information on the probabilities of detection for various respiratory pathogen diagnostic protocols with a hierarchical Bayesian model of pathogen prevalence. We demonstrated this application using four examples of diagnostic tests from three herds of bighorn sheep in Montana. For instance, one population with no detections of Mycoplasma ovipneumoniae (PCR assay) still had an 6% probability of the pathogen being present in the herd. Similarly, the apparent prevalence (0.32) of M. ovipneumoniae in another herd was a substantial underestimate of estimated true prevalence (0.46: 95% CI = [0.25, 0.71]). The negative bias of naïve prevalence increased as the probability of detection of testing protocols worsened such that the apparent prevalence of Mannheimia haemolytica (culture assay) in a herd (0.24) was less than one third that of estimated true prevalence (0.78: 95% CI = [0.43, 0.99]). We found a small difference in the estimates of the probability that Mannheimia spp. (culture assay) was present in one herd between the binomial sampling approach (0.24) and the hypergeometric approach (0.22). Ignoring the implications of imperfect detection and sampling variation for assessing pathogen communities in bighorn sheep can result in spurious inference on pathogen presence and prevalence, and potentially poorly informed management decisions. Our Shiny application makes the rigorous assessment of pathogen presence, prevalence and uncertainty straightforward, and we suggest it should be incorporated into a new paradigm of disease monitoring.

Testing the importance of harvest refuges for phenotypic rescue of trophy‐hunted populations

Abstract Sustainable exploitation must minimize its impact on the ecology and evolution of exploited wildlife. Intense phenotype‐based selective harvests can induce evolutionary change. Refuges could mitigate those evolutionary effects if individuals not subject to selective hunting in harvest refuges migrated and reproduced in hunted areas. The role of harvest refuges on phenotypic rescue of trophy‐hunted species, however, has rarely been tested. We investigated spatial and temporal variation in the effect of refuges on horn size and age at harvest in bighorn sheep Ovis canadensis. We analysed data on 5,826 males harvested over 39 years in Alberta, Canada. Horn length, a trait targeted by hunters, and age at harvest increased with the amount of protected areas 5–40 km around each kill. Horn base circumference, however, was independent of proximity to refuges. The number of males harvested increased during the last 10 days of the hunting season in late October, corresponding to the timing of bighorn male breeding migrations. Males shot during those 10 days were on average 17% closer to a refuge than males shot earlier in the season. Apparently, some large males exit refuges late in the hunting season, are shot, and cannot contribute to rescue. Uncertainty remains about the proportion of males exiting refuges after the hunting season and how many survive to reproduce. Synthesis and applications. Harvest refuges are unlikely to rescue hunted populations of bighorn sheep in Alberta, because some males exiting refuges are at risk of harvest before they mate. For phenotypic rescue to be effective, unselected males must reproduce before they are shot. Closing the hunting season 10 days earlier would increase survival of unselected rams exiting refuges.

Habitat predicts local prevalence of migratory behaviour in an alpine ungulate.

The resource hierarchy hypothesis predicts that the most important factors limiting a species' distribution act at the coarsest spatial scales. However, resource selection behaviour affords mobile organisms the opportunity to adopt a range of tactics for navigating spatial trade-offs between competing biotic and abiotic constraints. Throughout the animal kingdom, partial migration (where some individuals migrate, and others remain resident year round) offers a pervasive example of such behavioural polymorphism. Identifying the differences between these behaviours is therefore central to understanding the conditions (habitat) needed to sustain migrant and resident populations. Here we test an extension of the resource hierarchy hypothesis. We hypothesized that rather than responding to a single limiting factor, migration and residency represent contrasting scale-specific approaches to managing trade-offs between forage, predation risk and severe winter conditions. Furthermore, we predicted that the distribution of habitat selected by migrants and residents is predictive of the local prevalence of migratory behaviour. To test these hypotheses, we quantified migratory status- (resident/migrant) and season-specific (winter/summer) differences in resource selection by eight populations of federally endangered Sierra Nevada bighorn sheep Ovis canadensis sierrae across three spatial scales: population range, individual range and within individual range. We then integrated these spatial predictions to produce separate spatial predictions of migrant and resident winter habitat. As predicted, model selection provided strong evidence for the importance of status-specific differences in resource selection. Residents showed stronger coarse-scale selection for terrain associated with predator avoidance and stronger fine-scale selection for greenness, while in migrants this pattern was reversed. Availability of migrant habitat predicted the local prevalence of migration (top model pseudo R2 of .87). Our ability to respond to global declines of migratory species depends on improving our understanding of the conditions required to maintain migratory behaviour. Through explicitly contrasting migrant and resident behaviour, our results illustrate seasonal differences in migrant and resident habitat and how these two behaviours represent responses to different limiting conditions. Our analyses provides a novel empirical basis for assessing the local prevalence of migratory behaviour across large landscapes.

Desert bighorn sheep responses to human activity in south-eastern Utah

Abstract ContextHuman activity in wildlands can influence wildlife populations by decreasing or degrading habitat, decreasing survival, or through displacement. For bighorn sheep (Ovis canadensis), some human activities are detrimental and may result in physiological stress, altered activity budgets, or habitat abandonment. From 1979 to 2000, human recreation increased over 300% in areas occupied by desert bighorn sheep (O. c. nelsoni) in south-eastern Utah. Concurrently, the population of desert bighorn sheep occupying the Potash Bighorn Sheep Management Unit of south-eastern Utah was in steep decline. AimsWe investigated behavioural responses of desert bighorn sheep to different levels of human activity in this area from 2002 to 2003. MethodsWe divided the study population into two areas on the basis of the level of human use, i.e. low and high. We observed desert bighorn sheep at seven sites within these areas, including three with a high level of human use and four areas of a low level of human use. Key resultsDesert bighorn sheep spent significantly less time grazing and more time vigilant in areas of a high level of human use than in areas of a low level of human use. ConclusionsHuman recreational use of desert bighorn sheep habitat has the potential to negatively affect foraging by desert bighorn sheep. ImplicationsWe raise a cautionary flag because recreational use in bighorn sheep habitat near Moab, Utah, continues to increase and bighorn numbers continue to decline. When managers consider proposals to increase areas or trails for human recreation, they should incorporate ways to minimise impacts and reduce stressors to bighorn sheep.

Skull ontogeny of the pronghorn (Antilocapraamericana) in the comparative context of native North American ungulates

The pronghorn (Antilocapra americana (Ord, 1815)) is the single survivor of a largely extinct, isolated pecoran lineage (Antilocapridae) native to North America. We describe postnatal ontogeny of its skull in a comparative framework inclusive of representatives of other typical North American ungulate linages, all of which partially overlap in geographic distribution and share habitat with A. americana. To describe allometric growth, we took 23 linear cranial measurements in 30 specimens of A. americana and applied bi- and multi-variate statistics. The skull of A. americana generally grew with negative rates in width and height dimensions, and with positive rates in length, including an elongation of rostrum, particularly the nasals, and a relative narrowing of the braincase. We compared skull development in A. americana with development in two cervids (white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) and wapiti (Cervus canadensis Erxleben, 1777)) and two bovids (bighorn sheep (Ovis canadensis Shaw, 1804) and American bison (Bison bison (Linnaeus, 1758))). The multivariate ontogenetic trajectory of A. americana overlapped greatly with that of Odocoileus virginianus, and differed from the other species in varying degrees. These results indicated an essentially convergent pattern of skull growth with species showing important functional similarities, such as cervids of comparable size and feeding habits.

FIRST SPECIMEN RECORD OF BIGHORN SHEEP (OVIS CANADENSIS) FROM OKLAHOMA

On 21 September 2012, a dried carcass of a bighorn sheep (Ovis canadensis) was found near Black Mesa in the Oklahoma Panhandle. A complete skeleton (OMNH 55240) was salvaged and represents the first specimen record of the species in the state of Oklahoma.

Complete Mitochondrial Genome Sequence of Bighorn Sheep.

ABSTRACTWe report here the complete mitochondrial genome sequence of a Rocky Mountain bighorn sheep (Ovis canadensis) in the United States. The circular genome has a size of 16,466 bp and contains 13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes.

Dental enamel hypoplasias in Holocene bighorn sheep (Oviscanadensis) in eastern Washington state, USA

Dental enamel hypoplasias have been documented in extant and fossil mammal species and attributed to several kinds of physiological stress. They have not previously been reported among bighorn sheep (Ovis canadensis Shaw, 1804). Forty-six (36.8%) of 125 mandibular molars (m1, m2, m3) of bighorn recovered from disturbed Holocene archaeological deposits in eastern Washington state display several kinds of hypoplasias. The exact ontogenetic age of the individual animals when hypoplasias formed cannot be determined. The majority of the hypoplasias occur near the root–enamel junction of the m3, suggesting that most individuals were young adults when the defect formed. Physiological stress associated with reproductive costs, winter nutritional deficits, or both seems likely.

Population Dynamics of a Bighorn Sheep (Ovis canadensis) Herd in the Southern Black Hills of South Dakota and Wyoming

Abstract Bighorn sheep (Ovis canadensis) were re- introduced to the Black Hills of South Dakota and Wyoming beginning in 1965. Various pneumonia outbreaks caused populations to decline periodically, resulting in little to no lamb recruitment. An isolated population of bighorn sheep resides on Elk Mountain along the South Dakota-Wyoming border in the southern Black Hills. We estimated population size, survival, and recruitment rates of bighorn sheep on Elk Mountain by radio-collaring adult and neonatal sheep from 2012 to 2014. Overall annual ewe survival was 88.1% (se = 0.05), ram survival was 85.1% (se = 0.10), and 26 wk lamb survival was 44.7% (se = 0.09). Recruitment through 26 wk averaged 35% (SD = 0.02) across years. Population estimates for the 3 y were 80 (se = 0.58), 100 (se = 2.42), and 115 (se = 6.89) individuals, respectively. The Elk Mountain bighorn sheep herd experienced lamb survival and recruitment during 2012-2014; coupled with minor predation losses and a lack of deadly pneumonia, this he...

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.

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.

‘MigrateR’: extending model‐driven methods for classifying and quantifying animal movement behavior

To be useful, definitions of animal movement behavior (e.g. migration) should be quantitatively rigorous, flexible enough to accommodate variation in species biology (e.g. latitudinal vs elevational movement) and sufficiently general to allow comparison among different species. Recent studies have applied a model‐driven approach to classifying and quantifying animal movement from global positioning system (GPS) location data. We improve upon these methods by 1) revising model structure to provide a simple biologically‐defensible basis to reduce misclassification; 2) introducing a data‐efficient tool that can be used to quantify and circumvent model sensitivity to starting location; and 3) illustrating how existing models can be adapted to describe short‐distance migration, using elevational migration as an example. These improvements are included in ‘migrateR’, an open source R package that expands and automates model‐driven classification and quantification of animal movement behavior. We demonstrate the software and these improved methods using GPS‐collar location data from a long‐distance migrant, elk Cervus elaphus, and a short‐distance elevational migrant, Sierra Nevada bighorn sheep Ovis canadensis sierrae. We provide in‐text example code and a supplementary script illustrating how default options can be revised to meet several common challenges in fitting movement models.

Environmental and evolutionary effects on horn growth of male bighorn sheep

The development of male secondary sexual characters such as antlers or horns has substantial biological and socio‐economic importance because in many species these traits affect male fitness positively through sexual selection and negatively through trophy hunting. Both environmental conditions and selective hunting can affect horn growth but their relative importance remains unexplored. We first examined how a large‐scale climate index, the Pacific Decadal Oscillation (PDO), local weather and population density influenced both absolute and relative annual horn growth from birth to three years of male bighorn sheep Ovis canadensis over 42 years. We then examined the relative influence of environmental conditions and evolution mainly driven by trophy hunting on male horn length at three years of age. Horn growth was positively influenced by low population density and warm spring temperature, suggesting that ongoing climate change should lead to larger horns. Seasonal values of PDO were highly correlated. Horn growth increased with PDO in spring or summer at low density, but was weak at high density regardless of PDO. The interaction between population density and PDO in spring or summer accounted for a similar proportion of the observed annual variation in horn growth (32% or 37%) as did the additive effects of spring temperature and density (34%). When environmental conditions deteriorated, males allocated relatively more resources to summer mass gain than to horn growth, suggesting a conservative strategy favoring maintenance of condition over allocation to secondary sexual characters. Population density explained 27% of the variation in horn length, while evolutionary effects explained 9% of the variance. Thus, our study underlines the importance of both evolution and phenotypic plasticity on the development of a secondary sexual trait.

Genome Sequence of Bibersteinia trehalosi Strain Y31 Isolated from the Pneumonic Lung of a Bighorn Sheep.

Here, we report the genome sequence for Bibersteinia trehalosi strain Y31, isolated from the lungs of a bighorn sheep (Ovis canadensis) that had succumbed to pneumonia, which exhibits proximity-dependent inhibition (PDI) of Mannheimia haemolytica. The sequence will be used to understand the mechanism of PDI for these organisms.

Holocene mammalian change in the central Columbia Basin of eastern Washington state, USA

Abstract Predictions of changes in the Holocene mammalian fauna of the central Columbia Basin in eastern Washington (USA) based on environmental changes are largely met. Taxonomic richness is greatest during periods of cool-moist climate. Rates of input of faunal remains to the paleozoological record may suggest greater mammalian biomass during periods of greater moisture but are difficult to interpret without data on sampling intensity in the form of volume of sediment excavated. Abundances of leporids and grazing ungulates fluctuate in concert with abundance of grass. Several biogeographic records are tantalizing but require additional study and data before being accepted as valid. Records of red fox ( Vulpes vulpes ) indicate this species was present in the central basin during the Holocene contrary to historic records and recent suggestions modern foxes there are escapees from fur farms. Bison ( Bison bison ) and bighorn sheep ( Ovis canadensis ) underwent diminution of body size during the Holocene. Modern efforts to conserve the Columbia Basin ecosystem are advised to consider the Holocene record as indicative of what may happen to that ecosystem in the future.

Roads, routes and rams: does sexual segregation contribute to anthropogenic risk in a desert-dwelling ungulate?

Context Little is known about the consequences of sexual segregation (differential use of resources by the sexes outside of the mating season) for the conservation of large mammals. Roadways (i.e. the strip of land over which a road or route passes) are ubiquitous around the world, and are a major cause of wildlife mortality, as well as habitat loss and fragmentation. Many populations of bighorn sheep (Ovis canadensis) occur at low densities and in a metapopulation structure. Roadways could affect movements of males and females differentially, an outcome that has not been considered previously. Aims We investigated the propensity of the sexes to cross a paved two-lane road and a single-lane, maintained dirt route and predicted that adult males, because of their life-history characteristics, would cross those roadways more often than females. Methods We investigated movements of male and female bighorn sheep from 1986 to 1990. We used a fixed-wing aircraft with an H-antenna on each wing strut to locate individuals each week from October 1986 to December 1990. We estimated the degree of overlap among 50% core areas of use by males and females with the utilisation distribution overlap index (UDOI). Key results We relocated male and female bighorn sheep on 948 occasions during sexual aggregation and on 1951 occasions during sexual segregation. More males than females were likely to cross both types of roadways during segregation, and the dirt route during aggregation. Propensity of males and females to cross roadways was strongly influenced by time of year (i.e. whether the period of sexual aggregation or sexual segregation). The lowest overlap in 50% core areas was between females and males during periods of segregation (UDOI = 0.1447). Conclusions More males than females crossed Kelbaker Road and the unnamed dirt route during segregation, as well as the unnamed route during aggregation. Both of those features could affect males more than females, and could result in reductions in the use of habitat or increased mortality of bighorn sheep from vehicle collisions as a result of spatial segregation of the sexes. Implications During environmental review, biologists should consider sexual segregation when assessing potential anthropogenic effects on movements of bighorn sheep. Biologists also should consider sexual segregation and how roadways, even lightly traveled routes, affect movements of male and female ungulates differently before manipulating habitat, translocating animals, or constructing or modifying roadways.