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Context Conservation corridors must facilitate long-distance dispersal movements to promote gene flow, prevent inbreeding, and allow animals to shift ranges with climate change. Least-cost models are used to identify areas that support long-distance movement. These models rely on estimates of landscape resistance, which are typically derived from habitat suitability. Objectives We examine two key steps in estimating resistance from habitat suitability: choosing a procedure to estimate habitat suitability, and choosing a transformation function to translate habitat suitability into resistance. Methods We used linear and nonlinear functions to convert three types of habitat suitability estimates (from expert opinion, resource selection functions, and step selection functions) into resistances for elk ( Cervus canadensis ) and desert bighorn sheep ( Ovis canadensis nelsoni ). We evaluated the resulting resistance maps on an independent set of observed long-distance, prospecting movements. Results A negative exponential function best described the relationship between resistance values and habitat suitability for desert bighorn sheep indicating long-distance movers readily travel through moderately-suitable areas and avoid only the least suitable habitat. For desert bighorn sheep, all three suitability estimates performed better than chance, and resource and step selection functions outperformed expert opinion. For elk, all three suitability estimates performed the same as chance. Conclusions When designing corridors to facilitate long-distance movements of mobile animals, we recommend transforming habitat suitability into resistance with a negative exponential function. Use of an exponential transformation means that larger fractions of the landscape offer low resistance, allowing greater flexibility in where a corridor is located.

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. The authors present a novel approach to identifying seasonal habitat for partially migratory species. Through a case study of an endangered ungulate, they demonstrate that behavioral models accounting for migratory tactics can predict the local prevalence of migratory behavior. These methods have great potential to inform conservation priorities for migratory species.

ContextTopographic ruggedness has been examined in thousands of ecological studies and is a popular variable for characterizing habitat selection. Despite widespread adoption, ruggedness metrics are often applied uncritically and require systematic and thorough testing using both artificial landscapes and real-world applications.ObjectivesIn this paper we introduce a technique that removes the correlation of topographic ruggedness with curvature in order to more accurately represent fine-scale surface ruggedness.MethodsWe test our modified version of several ruggedness metrics against traditional ruggedness metrics using three ideal ruggedness criteria in artificial landscapes. We further tested our modified ruggedness measures using 449 real mountain ranges in Nevada, USA. Using desert bighorn sheep as a case study, we tested both modified and uncorrected ruggedness measures and slope in a multiscale context in order to examine habitat selection by female bighorn sheep.ResultsThe modified versions of the metrics passed all three criteria of the ideal ruggedness test and was able to accurately capture surface ruggedness. Modified versions of ruggedness differed from uncorrected versions by containing fewer highly rugged cells along ridgelines and drainages. Habitat relationships of desert bighorn sheep with ruggedness were scale-dependent, such that female sheep selected for steep slopes at fine spatial scales and ruggedness at moderate spatial scales.ConclusionsWe demonstrate that there are three components to ruggedness: elevation variation, aspect diversity, and surface ruggedness representing first, second, and third generation ruggedness indices. Our technique for removing underlying topographic variation provides an improved mapping of surface ruggedness and augments the other two generations of ruggedness metrics.

The availability of surface water is assumed by many wildlife managers to be important to desert bighorn sheep (Ovis canadensis nelsoni). Yet scientific evidence suggests bighorn sheep populations can sometimes fulfill their water requirements from forage alone. To investigate how water use changes with environmental conditions, we analyzed the surface water use and movement patterns of 4 desert bighorn populations across a range of meteorological conditions in the Mojave Desert in California, USA. We compared ground-based weather data to the daily use of surface water sources for 65 known individuals, and examined the movement patterns of 18 of these individuals with global positioning system collars in relation to visitation to surface water sources. Maximum daily temperature most closely predicted the percent of bighorn visiting water daily, with visitation increasing approximately 30% between 30°C and 40°C. Individual animals switched from a tortuous foraging movement to directed movement when accessing surface water. Day length, maximum daily temperature, minimum daily temperature, solar radiation, and the interaction between day length and minimum temperature explained the distance desert bighorn were located from the nearest water source. Our results indicate that local meteorological conditions are important determinants of desert bighorn surface water use, and that managers should monitor water sources when the maximum daily temperature exceeds 35°C. Individual animals meet their water requirements with surface water under hot and dry conditions, likely because it is temporally or energetically efficient given their other resource needs.

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.

Terrain ruggedness is often an important variable in wildlife habitat models. Most methods used to quantify ruggedness are indices derived from measures of slope and, as a result, are strongly correlated with slope. Using a Geographic Information System, we developed a vector ruggedness measure (VRM) of terrain based on a geomorphological method for measuring vector dispersion that is less correlated with slope. We examined the relationship of VRM to slope and to 2 commonly used indices of ruggedness in 3 physiographically different mountain ranges within the Mojave Desert of the southwestern United States. We used VRM, slope, distance to water, and springtime bighorn sheep (Ovis canadensis nelsoni) adult female locations to model sheep habitat in the 3 ranges. Using logistic regression, we determined that the importance of ruggedness in habitat selection remained consistent across mountain ranges, whereas the relative importance of slope varied according to the characteristic physiography of each range. Our results indicate that the VRM quantifies local variation in terrain more independently of slope than other methods tested, and that VRM and slope distinguish 2 different components of bighorn sheep habitat.

Isolation of small populations is expected to reduce fitness through inbreeding and loss of genetic variation, impeding population growth and compromising population persistence. Species with long generation time are the least likely to be rescued by evolution alone. Management interventions that maintain or restore genetic variation to assure population viability are consequently of significant importance. We investigated, over 27 years, the genetic and demographic consequences of a demographic bottleneck followed by artificial supplementation in an isolated population of bighorn sheep (Ovis canadensis). Based on a long‐term pedigree and individual monitoring, we documented the genetic decline, restoration and rescue of the population. Microsatellite analyses revealed that the demographic bottleneck reduced expected heterozygosity and allelic diversity by 6.2% and 11.3%, respectively, over two generations. Following supplementation, first‐generation admixed lambs were 6.4% heavier at weaning and had 28.3% higher survival to 1 year compared to lambs of endemic ancestry. Expected heterozygosity and allelic diversity increased by 4.6% and 14.3% after two generations through new alleles contributed by translocated individuals. We found no evidence for outbreeding depression and did not see immediate evidence of swamping of local genes. Rapid intervention following the demographic bottleneck allowed the genetic restoration and rescue of this bighorn sheep population, likely preventing further losses at both the genetic and demographic levels. Our results provide further empirical evidence that translocation can be used to reduce inbreeding depression in nature and has the potential to mitigate the effect of human‐driven environmental changes on wild populations.

ContextWhen human-made barriers impact wildlife by limiting habitat connectivity, simulation can reveal movements lost to fragmentation, strategies to restore corridor function, and potential benefits of corridor restoration.ObjectivesGuided by previous genetic research, we examined desert bighorn sheep movement near two highways that restrict gene flow and modelled their movement and habitat selection behavior. The ultimate goal was to simulate movement without highway barriers as a means to site crossing structures that mitigate fragmentation and to reveal their benefits for habitat reachability.MethodsWe fit integrated step selection functions (iSSFs) to GPS data from 9 bighorn populations near highways in California. After comparing iSSF simulations to validation data, we simulated 8200 bighorn-years of movement—200 year-long tracks each for 41 individuals—on a landscape with and without highways. We derived utilization distributions (UD) from simulations to identify probable high-use locations along the highways, compare these locations to previously predicted genetic corridors and roadkill events, and estimate changes in habitat reachability and elevation without these barriers.ResultsSimulation UDs correlated well with observed bighorn movements. Barrier-free simulations indicated preferred corridors across highway-blocked valleys, often at the same locations predicted by landscape genetics models (4 of 6 genetic-based corridors matched simulation-based corridors), and where bighorn roadkill events occurred (3 of 3 roadkill events occurred at simulation-predicted corridors). Relative to barrier-present simulations, barrier removal increased accessible habitat for 8 of 9 populations, with increases ranging from 7 to 138% per population. Barrier-free conditions allowed movement to higher elevations in two populations.ConclusionAnimal movement simulation can effectively assess fragmentation impacts and reveal mitigation options when other data sources are scarce. Our simulations confirm previously predicted corridors, provide detailed locations for targeted mitigation, and suggest certain corridors pose greater habitat-related benefits.

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

To improve lifetime reproductive success, maternal ungulates should pursue behavioral strategies that reduce risk of offspring mortality. Predation is a leading cause of neonatal mortality; thus, maternal ungulates should select habitat that reduces risk of predation on vulnerable neonates. We examined selection of habitat across subpopulations of federally endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae) within Sierra Nevada, California, USA, 2008–2018. Our objectives were to understand how maternal Sierra Nevada bighorn minimize risk of predation through selection of habitat and to quantify current and future potential neonatal habitat across the Sierra Nevada. Mountain lions (Puma concolor) are the predominant predators of adult Sierra Nevada bighorn; thus, we hypothesized females would select habitat that minimized risk of predation from mountain lions. We developed a used-available resource selection function to quantify patterns of habitat selection and produced predictive maps identifying highly selected lambing habitat across the Sierra Nevada. Our top model demonstrated females selected habitat where the relative probability of encountering mountain lions was low and near escape terrain. Selection for vegetation type was dependent on risk of encounter with mountain lions; when risk of encounter was low, females selected shrub cover. This suggests that when risk of encountering mountain lions was low, females may have selected areas with dense shrubs to reduce risk of being detected by other predators such as coyotes (Canis latrans) and golden eagles (Aquila chrysaetos). As risk of encountering mountain lions increased, females avoided all vegetation types other than barren, suggesting that despite increased risk of encounter, females may have been able to mitigate overall mortality risk by selecting habitat where approaching mountain lions could be detected and avoided. Our predictive models and resulting maps demonstrate differences in prevalence and connectivity of highly selected lambing habitat across subpopulations, which may explain differences in lamb recruitment and adequacy of lambing habitat observed among subpopulations. Recolonization into historical ranges and increasing connectivity between Sierra Nevada bighorn subpopulations is an important conservation need for species recovery and long-term viability of fragmented subpopulations.