Animal movements among habitat patches or populations are important for maintaining long-term genetic and demographic viability, but connectivity may also facilitate disease spread and persistence. Understanding factors that influence animal movements is critical to understanding potential transmission risk and persistence of communicable disease in spatially structured systems. We evaluated effects of sex, age and Mycoplasma ovipneumoniae infection status at capture on intermountain movements and seasonal movement rates observed in desert bighorn sheep ( Ovis canadensis nelsoni ) using global positioning system collar data from 135 individuals (27 males, 108 females) in 14 populations between 2013 and 2018, following a pneumonia outbreak linked to the pathogen M. ovipneumoniae in the Mojave Desert, California, USA. Based on logistic regression analysis, intermountain movements were influenced by sex, age and most notably, infection status at capture: males, older animals and uninfected individuals were most likely to make such movements. Based on multiple linear regression analysis, females that tested positive for M. ovipneumoniae at capture also had lower mean daily movement rates that were further influenced by season. Our study provides empirical evidence of a pathogenic infection decreasing an individual's future mobility, presumably limiting that pathogen's ability to spread, and ultimately influencing transmission risk within a spatially structured system.

Quantifying unique morphological characteristics of an animal is important to create a record as conditions change over time, as well as to characterize adaptations that may be unique to specific populations, particularly those that are rare or endangered. We investigated morphologic differences among bighorn sheep (Ovis canadensis) in California. There are three geographically distinct populations of bighorn sheep in California that are currently recognized and managed under different conservation strategies: Sierra Nevada bighorn (O. c. sierrae), desert bighorn (O. c. nelsoni), and Peninsular bighorn (O. c. nelsoni). We analyzed morphologic measurements recorded for these populations between 1978 and 2016 to quantify their physical characteristics and determine if there are differences among them. Body and horn characteristics were unique for each population. Sierra bighorn tended to have larger body size and smaller horns than Peninsular and desert bighorn, and Peninsular bighorn tended to weigh more and have larger horns than desert bighorn (Sierra males weighed 22% more than desert males; Peninsular males weighed 14% more than desert males). Distinctions among rare and endangered populations, like Sierra Nevada and Peninsular bighorn sheep, have important implications for wildlife managers.

1. Energy stores and migration are important adaptations for animals in seasonal environments, but their roles may vary relative to an animal's endogenous and exogenous environment. In partially migratory populations, migrants and residents experience different seasonal environments; thus, the influence of energy stores on survival may differ relative to migratory tactic, with potential consequences to survival and fitness. 2. Using data from Sierra Nevada bighorn sheep ( Ovis canadensis sierrae ; hereafter, Sierra bighorn), we tested the hypothesis that body fat (energy stores) buffers animals against their environment, but that buffering capacity differs across environments experienced by high-elevation residents (using a single range year-round), traditional migrants (making 1 round-trip movement between high-and

Seasonal migration is a behavioral response to predictable variation in environmental resources, risks, and conditions. In behaviorally plastic migrants, migration is a conditional strategy that depends, in part, on an individual’s informational state. The cognitive processes that underlie how facultative migrants understand and respond to their environment are not well understood. We compared perception of the present environment to memory and omniscience as competing cognitive mechanisms driving altitudinal migratory decisions in an endangered ungulate, the Sierra Nevada bighorn sheep ( Ovis canadensis sierrae ) using 1,298 animal years of data, encompassing 460 unique individuals. We built a suite of statistical models to partition variation in fall migratory status explained by cognitive predictors, while controlling for non-cognitive drivers. To approximate attribute memory, we included lagged attributes of the range an individual experienced in the previous year. We quantified perception by limiting an individual’s knowledge of migratory range to the area and attributes visible from its summer range, prior to migrating. Our results show that perception, in addition to the migratory propensity of an individual’s social group, and an individual’s migratory history are the best predictors of migration in our system. Our findings suggest that short-distance altitudinal migration is, in part, a response to an individual’s perception of conditions on alterative winter range. In long-distance partial migrants, exploration of migratory decision-making has been limited, but it is unlikely that migratory decisions would be based on sensory cues from a remote target range. Differing cognitive mechanisms underpinning short and long-distance migratory decisions will result in differing levels of behavioral plasticity in response to global climate change and anthropogenic disturbance, with important implications for management and conservation of migratory species.

Infectious disease transmission from domestic sheep threatens the persistence of bighorn sheep (Ovis canadensis) populations throughout western North America. Quantifying spatial separation between the 2 species is an essential component in assessing the risk of disease transmission. We present a spatial analysis to evaluate infectious disease risks for endangered Sierra Nevada bighorn sheep (O. c. sierrae; hereafter Sierra bighorn sheep). Our approach accounted for spatial separation between the species as well as the configuration of resources that influences Sierra bighorn sheep movement. We assessed the potential for contact by predicting where Sierra bighorn sheep were likely to be located and travel. We combined a resource selection probability function with a cost distance analysis to quantify the risk of grazing domestic sheep in proximity to Sierra bighorn sheep core home range from a habitat perspective. We compared our approach to a standard buffer approach and determined that our cost distance model better quantified how risk varied among grazing parcels. Sierra bighorn sheep selected and traveled within habitat that included escape terrain. Our model, which included a log normal transformation, characterized the high relative cost (i.e., reduced likelihood) to traveling beyond selected habitat and predicted that such movement is less likely. As a result, our habitat-based risk threshold was 48% smaller in area than the standard buffer area that included landscape that bighorn did not use. Our method establishes a risk threshold that can be used by land managers to optimize public and private grazing regimes and minimize the risk of disease transmission.

Wildlife capture, and the data collection associated with it, has led to major advancements in ecology that are integral to decision making pertaining to wildlife conservation. Capturing wildlife, however, can cause lethal and non-lethal risks to animals. Understanding the factors that contribute to the level of risk involved in wildlife capture is therefore important for the development and implementation of the safest and most effective methodologies. We used data from 736 animal captures of 389 individuals for 2 subspecies of female bighorn sheep (Rocky Mountain bighorn [Ovis canadensis canadensis], Sierra Nevada bighorn sheep [O. c. sierrae]) in Wyoming and California, USA, in 2002-2020 to evaluate the degree and extent of time that capture via helicopter net-gunning affects survival. We compared pre- and post-capture survival during a 10-week window centered on a capture event, and post-capture survival between captured animals and animals that were monitored but not captured during the 10-week window. Additionally, we evaluated the effects of handling techniques (number of times captured, season of capture event, handling time, chase time, and body temp) and biological factors (age and nutritional condition) on probability of capture mortality. Mean daily survival was 0.9992 during a 5-week pre-capture window, dropped to 0.9864 on the day of capture, and rebounded within 3 days of capture to pre-capture levels and that of sheep that were not captured. Overall, direct mortality resulting from capture was 1.36%, with 0.54% mortality occurring within the 3 days following a capture event for an overall 1.90% capture-related mortality. The only handling and biological metrics that influenced the probability of capture mortality were rectal temperature and nutritional condition; high initial rectal temperatures and poor body condition were associated with increased risk of mortality in the days following capture. Overall, helicopter net-gunning imposed low and short-term risk to survival of female bighorn sheep. To reduce bias in survival estimates, we recommend using a 3-day censorship window for post-capture mortalities as opposed to the common practice of a 2-5-week censor window. Helicopter net-gunning, including annual or seasonal recaptures, remains an effective and comparatively safe technique for capture and associated data collection of bighorn sheep.

Translocation of animals into formerly occupied habitat is a key element of the recovery plan for Sierra Nevada bighorn sheep (Ovis canadensis sierrae), which are state (California) and federally listed as endangered. However, implementing Sierra bighorn translocations is a significant conservation challenge because of the small size of the extant population and the limited number of herds available to donate translocation stock. One such herd, the Mt. Langley herd, recently became unusable as a translocation source following a substantial population decline. At the time of listing in 1999, predation by mountain lions (Puma concolor; hereafter lion) was considered a primary threat to Sierra bighorn, and since then lion predation may have continued to limit the ability of source herds to provide translocation stock. We evaluated the relationship between lion predation and ewe survival rates within three source herds of the Southern Recovery Unit, compared lion abundance and ewe survival among years of varying predation levels, provided a range of estimated times for the Mt. Langley herd to recover to its former status as a translocation source, and determined if the rates lions have been removed to mitigate Sierra bighorn predation exceeded sustainable harvest guidelines. We found compelling evidence that lion predation has impeded the recovery of Sierra bighorn by reducing survival rates of adult ewes (and consequently, population growth) and by preying upon individuals that could have otherwise been translocated. Ewe survival was poor during years of extreme predation but even during years of typical predation, survival rates were below a level needed to ensure population growth, indicating that years with little or no lion predation may be necessary for the population to grow and meet recovery goals. Because the intensity of predation was related to lion abundance, monitoring lion populations could provide managers with advance warning of periods of extreme predation. We found that following a period of particularly extreme predation, the Mt. Langley herd decreased in abundance far below the threshold needed to be considered a source of translocation stock, resulting in the loss of approximately 25% of the recovery program’s capacity for translocations. It is unclear how many years it will take for this herd to recover, but management actions to reduce lion predation are likely needed for this herd to grow to a size that can afford to donate individuals to translocation efforts in the near future, even when optimistic growth rates are assumed. We found that lion removal may also be needed to prevent predation from leading to Sierra bighorn population decline. Lion removal rates that have been implemented thus far are well below what would be needed to reduce the abundance the eastern Sierra lion population itself. We recommend continued monitoring of Sierra bighorn and sympatric lions and note that lion removal may be required to facilitate bighorn recovery for the foreseeable future.

ABSTRACT Wildlife managers often need to estimate population abundance to make well‐informed decisions. However, obtaining such estimates can be difficult and costly, particularly for species with small populations, wide distributions, and spatial clustering of individuals. For this reason, DNA surveys and capture–recapture modeling has become increasingly common where direct observation is consistently difficult or counts are small or variable. We compared the precision, as indicated by the coefficient of variation (CV), and cost‐effectiveness of 2 methods to estimate abundance of desert bighorn sheep ( Ovis canadensis nelsoni ) populations: traditional ground‐based mark–resight and fecal DNA capture–recapture. In the Marble Mountains in the Mojave Desert of southeastern California, USA, we conducted annual ground‐based mark–resight surveys and collected fecal samples at water sources concurrently during the dry seasons (Jun–Jul) of 2016 and 2017. Fecal DNA samples were genotyped to identify unique individuals. The Lincoln–Peterson bias‐corrected estimator and Huggins closed‐capture recapture models were used to estimate abundance for the ground‐based mark resight and fecal DNA capture–recapture, respectively. We compared costs between the 2 methods for our study and used simulations to estimate costs for a variety of possible sampling scenarios for our study system based on field‐based estimates. Population abundance estimates from fecal DNA capture–recapture achieved much greater precision (CV = 5–7%) than estimates derived from ground‐based mark–resight (CV = 21–56%). Our simulations indicated that for a population of 100, 2 sampling occasions, and resight probability of 0.20, the lowest CV obtained by mark–resight was approximately 12%. We predict the cost of abundance estimates for this level of precision (CV = 12%) from fecal DNA capture–recapture would be 28% of the cost of ground‐based mark–resight (i.e., a 72% cost reduction). We conclude that fecal DNA capture–recapture is a highly cost‐effective alternative for estimating abundance of relatively small populations (≤300) of desert bighorn sheep. More broadly, integrating simulated study designs with cost analyses provides a tool to identify the most effective method for estimating abundance over a wide variety of sampling scenarios. © 2020 The Wildlife Society.

Energy is fundamentally important to life and when energy supplies cannot support energy demands, animals may reduce energy deficits through behavioral compensation-a phenomenon that can vary with physiological state (state dependent) or environmental conditions (context dependent). We built an energetics model to estimate seasonal and annual energy expenditures by female Sierra Nevada bighorn sheep (Ovis canadensis sierrae; hereafter, Sierra bighorn) and evaluated whether energy expenditures by Sierra bighorn were consistent with behavioral compensation. We parameterized the model with values from the literature for energy expenditures for metabolism, feeding, locomotion, tissue synthesis, and reproduction in bighorn sheep and populated the model with empirical data (body mass, ingesta-free body fat, reproductive state, and daily movements) from female Sierra bighorn. Annual energy expenditures by reproductive females (7,182 MJ x yr(-1)) were similar to 42% greater than annual energy expenditures by non-reproductive females (5,066 MJ x yr(-1)). Regardless of reproductive state, female Sierra bighorn expended less energy on activity in winter compared with summer, which was consistent with context-dependent (environmental) behavioral compensation. Results for state-dependent behavioral compensation were ambiguous, but daily movements and associated energy expenditures decreased over winter, coincident with declines in body fat. Our energy model can be adapted to any free ranging ungulate, if annual body mass and fat dynamics, metabolic rates, reproductive state, and daily movements are known. Coupling our model with estimates of food supplies may generate deeper insights regarding energetic motivations of migration and habitat use.

Bighorn sheep (Ovis canadensis) can live in extremely harsh environments and subsist on submaintenance diets for much of the year. Under these conditions, energy stored as body fat serves as an essential reserve for supplementing dietary intake to meet metabolic demands of survival and reproduction. We developed equations to predict ingesta-free body fat in bighorn sheep using ultrasonography and condition scores in vivo and carcass measurements postmortem. We then used in vivo equations to investigate the relationships between body fat, pregnancy, overwinter survival, and population growth in free-ranging bighorn sheep in California and Nevada. Among 11 subpopulations that included alpine winter residents and migrants, mean ingesta-free body fat of lactating adult females during autumn ranged between 8.8% and 15.0%; mean body fat for nonlactating females ranged from 16.4% to 20.9%. In adult females, ingesta-free body fat > 7.7% during January (early in the second trimester) corresponded with a > 90% probability of pregnancy and ingesta-free body fat > 13.5% during autumn yielded a probability of overwinter survival > 90%. Mean ingesta-free body fat of lactating females in autumn was positively associated with finite rate of population increase (λ) over the subsequent year in bighorn sheep subpopulations that wintered in alpine landscapes. Bighorn sheep with ingesta-free body fat of 26% in autumn and living in alpine environments possess energy reserves sufficient to meet resting metabolism for 83 days on fat reserves alone. We demonstrated that nutritional condition can be a pervasive mechanism underlying demography in bighorn sheep and characterizes the nutritional value of their occupied ranges. Mountain sheep are capital survivors in addition to being capital breeders, and because they inhabit landscapes with extreme seasonal forage scarcity, they also can be fat reserve obligates. Quantifying nutritional condition is essential for understanding the quality of habitats, how it underpins demography, and the proximity of a population to a nutritional threshold.

ABSTRACTSurvival in small populations (e.g., Sierra Nevada bighorn sheep or Sierra bighorn [Ovis canadensis sierrae]) is often highly variable. External selective pressures vary in the degree to which they regulate survival by sex and age class. Understanding the important factors and risks for different demographic classes helps managers design strategies that enhance the recovery of endangered species, including Sierra bighorn. Our goal was to determine what population‐level factors (e.g., climate, habitat, population size, predation) affect survival and whether there are interactions between these factors by age and sex, and then apply our findings to recovery strategies. To this end, we conducted a known‐fate survival analysis for female and male Sierra bighorn with data collected over 12 years, and used model selection to evaluate models with spatial, environmental, and other population‐level factors hypothesized to be related to survival. Survival of adult Sierra bighorn declined continuously with age for both sexes; survival was generally higher for females than males, and there were no interactions between age and any environmental or population‐level factors. The top model for both sexes included the date of peak value of normalized difference vegetation index (NDVI) from the previous summer; NDVI had a similar positive relationship with survival for both sexes, which indicates that the later the growing season persists into the summer, the better survival the subsequent year. For females, survival also was negatively related to an index of abundance for mountain lions (Puma concolor), whereas the relationship was less apparent for males. Instead, top models for males indicated elevated survival during warm wet years, but years with late peaks in NDVI the previous year ameliorated the effect of a cold, dry winter. Finally, competitive models for males and females included a variable representing avalanche risk, indicating reduced survival in areas with increased avalanche risk. From a recovery management perspective, the lack of any interaction between age and other covariates suggests that although we may still select younger female Sierra bighorn for translocations (an essential recovery action) because they have higher reproductive value than old females, there were no additional negative synergies between age and other factors to consider. All variables are of value in guiding expectations for newly established populations and established source populations and some may help fine tune the selection of translocation areas. In addition, including predation, weather covariates, and catastrophic effects, such as avalanche risk, in projection models is important for realistic estimation of the time required to meet recovery goals and predicting population trajectories under likely climate change scenarios. Our approach is generalizable to other systems; we demonstrated how survival analyses can inform endangered species recovery management by indicating ideal areas for translocations and provided realistic estimates of time‐to‐recovery or other recovery metrics. © 2018 The Wildlife Society.

Migratory species face well-documented global declines, but the causes of these declines remain unclear. One obstacle to better understanding these declines is uncertainty surrounding how migratory behavior is maintained. Most migratory populations are partially migratory, displaying both migrant and resident behaviors. Theory only provides two possible explanations for this coexistence of migration and residency: either these behaviors are fixed at the individual level or both behaviors are part of a single conditional strategy in which an individual’s migratory status (adoption of migrant or resident behavior) is plastic. Here we test for plasticity in migratory status and tactics (timing, distance, and duration of migration) in a federally endangered mountain caprid, the Sierra Nevada bighorn sheep (Ovis canadensis sierrae Grinnell, 1912). We used nonlinear modeling to quantitatively describe migratory behavior, analyzing 262 animal-years of GPS location data collected between 2005 and 2016 from 161 females across 14 subpopulations. Migratory tactics and prevalence varied by subpopulation. On average, individuals from partially migratory subpopulations switched migratory status every 4 years. Our results support the hypothesis that partial migration is maintained through a single conditional strategy. Understanding plasticity in migratory behavior will improve monitoring efforts and provide a rigorous basis for evaluating threats, particularly those associated with changing climate.

Complete List of Authors: Spitz, Derek; University of Montana, Wildlife Biology Program, W. A. Franke College of Forestry and Conservation Hebblewhite, Mark; University of Montana, Wildlife Biology Program, W.A. Franke College of Forestry and Conservation Stephenson, Thomas; California Department of Fish and Wildlife, Sierra Nevada Bighorn Sheep Recovery Program German, David; California Department of Fish and Wildlife, Sierra Nevada Bighorn Sheep Recovery Program

We evaluated the consequences of different predator management strategies and the subsequent effects on time and cost to recovery for federally endangered Sierra Nevada bighorn sheep. Based on data collected during 1995-2009, we used stage based demographic modeling to estimate vital rates in three isolated herds, accounting for sampling error and variance. Using those vital rates we predicted the time and associated cost for the population to meet delisting goals. We found recovery time increased from 17.3 to 28.6 years using a density independent model and from 25.9 to 38.6 years using a density dependent model for different mountain lion management strategies. Commensurate cost increases of over 10 million dollars (unadjusted cost) result in either case. Our study suggests that appropriate levels of predator management will result in shorter recovery times and reduced cost of recovery through ensuring the availability of translocation stock. To be most effective, mountain lion management strategies should be population-specific because of underlying differences in predation rates for different herds.

Pack stock (horses, mules, burros, llamas, and goats) are frequently assumed to have negative effects on public lands, but there is a general lack of data to be able to quantify the degree to which this is actually the case. Sequoia and Kings Canyon National Parks have received complaints that pack stock may affect Sierra Nevada bighorn sheep (Ovis canadensis sierrae; SNBS), a federally endangered subspecies that occurs in largely disjunct herds in the Sierra Nevada Range of California. The potential effects are thought to be displacement of SNBS from meadows on their summer range (altered habitat use) or, more indirectly, through changes in SNBS habitat or forage quality. Our goals were to conduct an association analysis to quantify the degree of potential spatial overlap in meadow use between SNBS and pack stock and to compare differences in vegetation community composition, structure, and diversity among meadows with different levels of use by bighorn sheep and pack stock. For the association analysis, we used two approaches: (1) we quantified the proportion of meadows that were within the herd home ranges of bighorn sheep and were potentially open to pack stock, and, (2) we used Monte Carlo simulations and use-availability analyses to compare the proportion of meadows used by bighorn sheep relative to the proportional occurrence or area of meadows available to bighorn sheep that were used by pack stock. To evaluate potential effects of pack stock on meadow plant communities and SNBS forage, we sampled vegetation in 2011 and 2012 at 100 plots to generate data that allowed us to compare: 1. Herbaceous plant species composition, structure, and diversity in plots with different combinations of use by pack stock and SNBS; 2. Cover of bare ground in plots with different combinations of use by pack stock and SNBS; and, 3. Total cover, diversity, and species composition of SNBS forage species in plots with different combinations of use by pack stock and SNBS. The association analyses indicated the potential for overlap between pack stock and SNBS was minimal; only 1 percent of the potential meadow area in the SNBS herd home ranges overlapped that of pack stock meadows. There were no systematic differences in overall vegetation structure or composition, or in diversity, cover, or composition of forage species, that indicated pack stock were altering SNBS habitat or affecting their nutrition. Variation in plant species composition was influenced primarily by random differences among meadows and environmental gradients, and there was little evidence that pack stock use contributed in meaningful ways to this variation. The few differences among meadows with different levels of use by bighorn sheep and pack stock either were minor or were not in a direction consistent with negative effects of pack stock on SNBS. We conclude that the current plan for managing pack stock grazing has been successful in minimizing significant negative effects on Sierra Nevada bighorn sheep at Sequoia and Kings Canyon National Parks.

Predation can disproportionately affect endangered prey populations when generalist predators are numerically linked to more abundant primary prey. Apparent competition, the term for this phenomenon, has been increasingly implicated in the declines of endangered prey populations. We examined the potential for apparent competition to limit the recovery of Sierra Nevada bighorn sheep (Ovis canadensis sierrae), an endangered subspecies under the US Endangered Species Act. Using a combination of location, demographic, and habitat data, we assessed whether cougar (Puma concolor) predation on endangered bighorn sheep was a consequence of their winter range overlap with abundant mule deer (Odocoileus hemionus). Consistent with the apparent competition hypothesis, bighorn sheep populations with higher spatial overlap with deer exhibited higher rates of cougar predation which had additive effects on adult survival. Bighorn sheep killed by cougars were primarily located within deer winter ranges, even though those areas constituted only a portion of the bighorn sheep winter ranges. We suspect that variation in sympatry between bighorn sheep and deer populations was largely driven by differences in habitat selection among bighorn sheep herds. Indeed, bighorn sheep herds that experienced the highest rates of predation and the greatest spatial overlap with deer also exhibited the strongest selection for low elevation habitat. Although predator-mediated apparent competition may limit some populations of bighorn sheep, it is not the primary factor limiting all populations, suggesting that the dynamics of different herds are highly idiosyncratic. Management plans for endangered species should consider the spatial distributions of key competitors and predators to reduce the potential for apparent competition to hijack conservation success.