Bighorn Sheep Populations Research Articles

Doing what your neighbour does: neighbour proximity, familiarity and postural alignment increase behavioural mimicry

Nonconscious behavioural mimicry, acting similarly to one's social partner, is thought to be a core component of group cohesion and coordination. However, the mechanisms contributing to this phenomenon are poorly understood. Understanding why behaviour is mimicked in some contexts but not in others is an important step in developing hypotheses about how and why some behaviours spread between social partners. Here we examine mimicry of routine vigilance during grazing episodes in a population of free-ranging bighorn sheep, Ovis canadensis, rams. Results indicate that vigilance bouts are more likely to be mimicked when neighbouring rams are in closer proximity, more familiar with one another and posturally aligned. Additionally, older rams are more likely than young rams to mimic the vigilance bouts of others, and mimicry occurs more often when the initiating ram is lower ranking than the mimicking ram. We interpret these findings within the framework of biases in attentiveness to particular individuals as a possible mechanism leading to the occurrence of behavioural mimicry.

The Gordian knot of mountain lion predation and bighorn sheep

ABSTRACTThe objective of this review is to generate a synthesis of research conducted on predation of bighorn sheep (Ovis canadensis) and to suggest directions for future research relative to current knowledge gaps and a novel hypothesis. This review is primarily based on literature from the last 60 years on desert bighorn sheep (O. c. nelsoni), Rocky Mountain bighorn sheep (O. c. canadensis), and mountain lion (Puma concolor) predation. Although, many predators kill bighorn sheep, only mountain lions are currently considered to be the primary proximate cause of mortality for many bighorn sheep populations. The ultimate cause of this phenomenon has vexed wildlife managers for >40 years. There are 3 primary reasons for increased predation on bighorn sheep by mountain lions. First, there is an increased presence of mountain lions in habitats where they were historically absent or rare because of the expansion of mule deer (Odocoileus hemionus) following the extensive conversion of fire‐maintained grasslands to shrublands in the late‐1800s. Second, is the extirpation of the 2 dominant apex carnivores (wolves [Canis lupus] and grizzly bears [Ursus arctos]) during this same time period and a hypothesized numerical response of mountain lions to those extirpations. Finally, the response of mountain lions to the cessation of >70 years of intensive predator control has often resulted in unsustainable mountain lion‐bighorn sheep ratios, especially for desert bighorn sheep. Additionally, the effect of mountain lion predation is exacerbated by declines in bighorn sheep that do not result in declines in mountain lions because of their ability to prey switch to mule deer, elk (Cervus canadensis), or domestic cattle; kleptoparasitism of mountain lions kills, by ursids and canids, resulting in higher kill rates for mountain lions; and a possible ecological trap where adaptations derived over evolutionary time are no longer adaptive because of human‐induced changes in the sympatric apex predator guild. Control of mountain lions, when mountain lion‐ungulate ratios are high, might be required to protect small or endangered bighorn sheep populations, and to produce bighorn sheep for restoration efforts. © 2017 The Wildlife Society.

Pneumonia in bighorn sheep: Risk and resilience

ABSTRACTInfectious disease contributed to historical declines and extirpations of bighorn sheep (Ovis canadensis) in North America and continues to impede population restoration and management. Reports of pneumonia outbreaks in free‐ranging bighorn sheep following contact with domestic sheep have been validated by the results of 13 captive commingling experiments. However, ecological and etiological complexities still hinder our understanding and control of respiratory disease in wild sheep. In this paper, we review the literature and summarize recent data to present an overview of the biology and management of pneumonia in bighorn sheep. Many factors contribute to this population‐limiting disease, but a bacterium (Mycoplasma ovipneumoniae) host‐specific to Caprinae and commonly carried by healthy domestic sheep and goats, appears to be a primary agent necessary for initiating epizootics. All‐age epizootics are usually associated with significant population declines, but mortality rates vary widely and factors influencing disease severity are not well understood. Once introduced,M. ovipneumoniaecan persist in bighorn sheep populations for decades. Carrier females may transmit the pathogen to their susceptible lambs, triggering fatal pneumonia outbreaks in nursery groups, which limit recruitment and slow or prevent population recovery. The demographic costs of disease persistence can be equal to or greater than the impacts of the initial epizootic. Strain typing suggests that spillover ofM. ovipneumoniaeinto bighorn sheep populations from domestic small ruminants is ongoing and that consequences of spillover are amplified by movements of infected bighorn sheep across populations. Therefore, current disease management strategies focus on reducing risk of spillover from reservoir populations of domestic sheep and goats and on limiting transmission among bighorn sheep. A variety of techniques are employed to prevent contacts that could lead to transmission, including limiting the numbers and distribution of both wild and domestic species. No vaccine or antibiotic treatment has controlled infection in domestic or wild sheep and to date, management actions have been unsuccessful at reducing morbidity, mortality, or disease spread once a bighorn sheep population has been exposed. More effective strategies are needed to prevent pathogen introduction, induce disease fadeout in persistently infected populations, and promote population resilience across the diverse landscapes bighorn sheep inhabit. A comprehensive examination of disease dynamics across populations could help elucidate how disease sometimes fades out naturally and whether population resilience can be increased in the face of infection. Cross‐jurisdictional adaptive management experiments and transdisciplinary collaboration, including partnerships with members of the domestic sheep and goat community, are needed to speed progress toward sustainable solutions to protect and restore bighorn sheep populations. © 2017 The Wildlife Society.

Assessing respiratory pathogen communities in bighorn sheep populations: Sampling realities, challenges, and improvements.

Respiratory disease has been a persistent problem for the recovery of bighorn sheep (Ovis canadensis), but has uncertain etiology. The disease has been attributed to several bacterial pathogens including Mycoplasma ovipneumoniae and Pasteurellaceae pathogens belonging to the Mannheimia, Bibersteinia, and Pasteurella genera. We estimated detection probability for these pathogens using protocols with diagnostic tests offered by a fee-for-service laboratory and not offered by a fee-for-service laboratory. We conducted 2861 diagnostic tests on swab samples collected from 476 bighorn sheep captured across Montana and Wyoming to gain inferences regarding detection probability, pathogen prevalence, and the power of different sampling methodologies to detect pathogens in bighorn sheep populations. Estimated detection probability using fee-for-service protocols was less than 0.50 for all Pasteurellaceae and 0.73 for Mycoplasma ovipneumoniae. Non-fee-for-service Pasteurellaceae protocols had higher detection probabilities, but no single protocol increased detection probability of all Pasteurellaceae pathogens to greater than 0.50. At least one protocol resulted in an estimated detection probability of 0.80 for each pathogen except Mannheimia haemolytica, for which the highest detection probability was 0.45. In general, the power to detect Pasteurellaceae pathogens at low prevalence in populations was low unless many animals were sampled or replicate samples were collected per animal. Imperfect detection also resulted in low precision when estimating prevalence for any pathogen. Low and variable detection probabilities for respiratory pathogens using live-sampling protocols may lead to inaccurate conclusions regarding pathogen community dynamics and causes of bighorn sheep respiratory disease epizootics. We recommend that agencies collect multiples samples per animal for Pasteurellaceae detection, and one sample for Mycoplasma ovipneumoniae detection from at least 30 individuals to reliably detect both Pasteurellaceae and Mycoplasma ovipneumoniae at the population-level. Availability of PCR diagnostic tests to wildlife management agencies would improve the ability to reliably detect Pasteurellaceae in bighorn sheep populations.

Detection of bacterial-reactive natural IgM antibodies in desert bighorn sheep populations.

Ecoimmunology is a burgeoning field of ecology which studies immune responses in wildlife by utilizing general immune assays such as the detection of natural antibody. Unlike adaptive antibodies, natural antibodies are important in innate immune responses and often recognized conserved epitopes present in pathogens. Here, we describe a procedure for measuring natural antibodies reactive to bacterial antigens that may be applicable to a variety of organisms. IgM from desert bighorn sheep plasma samples was tested for reactivity to outer membrane proteins from Vibrio coralliilyticus, a marine bacterium to which sheep would have not been exposed. Immunoblotting demonstrated bighorn sheep IgM could bind to a variety of bacterial cell envelope proteins while ELISA analysis allowed for rapid determination of natural antibody levels in hundreds of individual animals. Natural antibody levels were correlated with the ability of plasma to kill laboratory strains of E. coli bacteria. Finally, we demonstrate that natural antibody levels varied in two distinct populations of desert bighorn sheep. These data demonstrate a novel and specific measure of natural antibody function and show that this varies in ecologically relevant ways.

Alternative foraging strategies enable a mountain ungulate to persist after migration loss

AbstractThe persistence of many migratory ungulate populations worldwide is threatened due to anthropogenic impacts to seasonal ranges and migration routes. While many studies have linked migratory ungulate declines to migration disruption or loss, very few have explored the underlying factors that determine whether a population perishes or persists. In some cases, populations undergo severe declines and extirpation after migration loss; however, others appear able to persist as residents. We predict that to persist, populations must replace the traditional benefits of migration by altering the foraging strategies they employ as residents within one seasonal range. We propose the alternative foraging strategies (AFS) hypothesis as a framework for identifying various behavioral strategies that populations may use to cope with migration loss. We tested the hypothesis using the formerly migratory Teton bighorn sheep population in northwest Wyoming, which ceased migrating over 60 yr ago, but has persisted as a resident population. We used global positioning system data to evaluate winter and summer habitat selection and seasonal elevational movements for 28 adult female bighorn sheep (Ovis canadensis) from 2008 to 2010. Resource selection functions revealed that bighorn sheep employ winter foraging strategies to survive as residents by seeking out rugged, high‐elevation, windswept ridgelines. Seasonal movement analyses indicated that bighorn sheep undergo a newly documented “abbreviated migration” strategy that is closely synchronized with vegetation green‐up patterns within their one range. Bighorn sheep descend 500 m in elevation and travel up to 10 km in spring, gaining access to newly emergent forage approximately 30 d before it appears on their high‐elevation winter and summer ranges. Our findings indicate that the Teton bighorn sheep population has persisted due to its habitat selection, AFS, and unique movement patterns, which allow migration loss to be mediated to some extent. The identification of AFS and the habitats that support them can help reveal the underlying benefits of migration and conserve populations in the face of future migration loss.

Capital vs. income‐dependent optimal birth date in two North American ungulates

AbstractPhenotypic plasticity in reproductive traits is of theoretical and applied interest as one avenue by which organisms might maintain an optimal annual reproductive routine in the face of cyclic and/or directional change in environmental conditions. We used long‐term, individual‐based data from parapatric populations of bighorn sheep (Ovis canadensis canadensis) and pronghorn (Antilocapra americana) to evaluate plasticity in breeding date, gestation duration, birth date, birth mass, and fetal growth rate in response to inter‐annual (cyclic) variation in indices of maternal energy income and expense. Traits in both species responded plastically to variation in maternal energy balance. However, despite nearly identical climate and similar vegetative habitat, plasticity was expressed in fundamentally different ways in the study species. Variation in bighorn birth date was primarily due to plasticity in breeding date, whereas variation in pronghorn birth date was primarily due to variation in gestation duration. Across traits, bighorn plastic responses were more consistent with explanations that invoked periodic energy surplus as the basis for plasticity, whereas pronghorn plastic responses were more consistent with explanations that invoked periodic energy deficiency. Later birth date was associated with increased fetal growth rate in bighorn but decreased fetal growth rate in pronghorn. Finally, we detected strong directional selection for early birth among bighorn mothers but found no evidence of selection on pronghorn birth date. Collectively, our results indicate markedly different maternal tactics for timing birth. Bighorn mothers appeared to use stored energy to subsidize the cost of birth prior to the local environmental optimum in an energy‐mediated competition with other females to minimize birth order rank. Pronghorn mothers, committed to high levels of energy allocation to offspring and subject therefore to frequent energy deficiency, timed birth conservatively to more closely match peak reproductive expenditure with peak energy income at the local environmental optimum.

Towards robust evolutionary inference with integral projection models.

Integral projection models (IPMs) are extremely flexible tools for ecological and evolutionary inference. IPMs track the distribution of phenotype in populations through time, using functions describing phenotype-dependent development, inheritance, survival and fecundity. For evolutionary inference, two important features of any model are the ability to (i) characterize relationships among traits (including values of the same traits across ages) within individuals, and (ii) characterize similarity between individuals and their descendants. In IPM analyses, the former depends on regressions of observed trait values at each age on values at the previous age (development functions), and the latter on regressions of offspring values at birth on parent values as adults (inheritance functions). We show analytically that development functions, characterized this way, will typically underestimate covariances of trait values across ages, due to compounding of regression to the mean across projection steps. Similarly, we show that inheritance, characterized this way, is inconsistent with a modern understanding of inheritance, and underestimates the degree to which relatives are phenotypically similar. Additionally, we show that the use of a constant biometric inheritance function, particularly with a constant intercept, is incompatible with evolution. Consequently, current implementations of IPMs will predict little or no phenotypic evolution, purely as artefacts of their construction. We present alternative approaches to constructing development and inheritance functions, based on a quantitative genetic approach, and show analytically and through an empirical example on a population of bighorn sheep how they can potentially recover patterns that are critical to evolutionary inference.

Short-Term Impacts of Fire-Mediated Habitat Alterations on an Isolated Bighorn Sheep Population

Habitat alterations may improve and expand wildlife habitats, and bolster waning wildlife populations. We used global positioning system (GPS) locations to monitor 38 bighorn sheep (Ovis canadensis Shaw) that were translocated to the Seminoe Mountains, Wyoming, USA, in 2009 and 2010, and 24 bighorns captured in 2011 to investigate short-term impacts of prescribed fires and wildfires that covered ∼24% of the study area in 2011 and 2012. We quantified home range distributional changes, resource selection, and survival of bighorn sheep from 2009 to 2013. Although bighorns expanded home ranges and increased proportional use of fire-treated areas, there was no overall selection for fire-treated areas. Bighorn survival decreased by over 30% after fires in 2012 that were accompanied by severe drought. Prescribed fires conducted under favorable conditions (2011) induced potentially positive bighorn responses including high survival and increased use of treated areas. Fires during drought conditions were more widespread with little vegetative response (2012) and coincided with increased bighorn mortality in spring 2013. Dead bighorns with poor body condition had high home range overlap with burned areas. We suggest that large fires coupled with unfavorable weather conditions rendered bighorns unable to access adequate forage to meet nutritional requirements. Because impacts of fires on bighorn populations are highly dependent on ensuing vegetative recovery, consideration should be given to the timing, extent, and spatial coverage of prescribed fires. Therefore, we recommend conducting prescribed fires before bighorn reintroductions, or conducting prescribed fires on a relatively small scale and on a rotational basis to avoid reducing foraging options.

Behavioral connectivity among bighorn sheep suggests potential for disease spread

ABSTRACTConnectivity is important for population persistence and can reduce the potential for inbreeding depression. Connectivity between populations can also facilitate disease transmission; respiratory diseases are one of the most important factors affecting populations of bighorn sheep (Ovis canadensis). The mechanisms of connectivity in populations of bighorn sheep likely have implications for spread of disease, but the behaviors leading to connectivity between bighorn sheep groups are not well understood. From 2007–2012, we radio‐collared and monitored 56 bighorn sheep in the Salmon River canyon in central Idaho. We used cluster analysis to define social groups of bighorn sheep and then estimated connectivity between these groups using a multi‐state mark‐recapture model. Social groups of bighorn sheep were spatially segregated and linearly distributed along the Salmon River canyon. Monthly probabilities of movement between adjacent male and female groups ranged from 0.08 (±0.004 SE) to 0.76 (±0.068) for males and 0.05 (±0.132) to 0.24 (±0.034) for females. Movements of males were extensive and probabilities of movement were considerably higher during the rut. Probabilities of movement for females were typically smaller than those of males and did not change seasonally. Whereas adjacent groups of bighorn sheep along the Salmon River canyon were well connected, connectivity between groups north and south of the Salmon River was limited. The novel application of a multi‐state model to a population of bighorn sheep allowed us to estimate the probability of movement between adjacent social groups and approximate the level of connectivity across the population. Our results suggest high movement rates of males during the rut are the most likely to result in transmission of pathogens among both male and female groups. Potential for disease spread among female groups was smaller but non‐trivial. Land managers can plan grazing of domestic sheep for spring and summer months when males are relatively inactive. Removal or quarantine of social groups may reduce probability of disease transmission in populations of bighorn sheep consisting of linearly distributed social groups. © 2016 The Wildlife Society.

Evidence for strain‐specific immunity to pneumonia in bighorn sheep

ABSTRACTTransmission of pathogens commonly carried by domestic sheep and goats poses a serious threat to bighorn sheep (Ovis canadensis) populations. All‐age pneumonia die‐offs usually ensue, followed by asymptomatic carriage of Mycoplasma ovipneumoniae by some of the survivors. Lambs born into these chronically infected populations often succumb to pneumonia, but adults are usually healthy. Surprisingly, we found that introduction of a new genotype (strain) of M. ovipneumoniae into a chronically infected bighorn sheep population in the Hells Canyon region of Washington and Oregon was accompanied by adult morbidity (100%) and pneumonia‐induced mortality (33%) similar to that reported in epizootics following exposure of naïve bighorn sheep. This suggests an immune mismatch occurred that led to ineffective cross‐strain protection. To understand the broader context surrounding this event, we conducted a retrospective analysis of M. ovipneumoniae strains detected in 14 interconnected populations in Hells Canyon over nearly 3 decades. We used multi‐locus sequence typing of DNA extracts from 123 upper respiratory tract and fresh, frozen, and formalin‐fixed lung samples to identify 5 distinct strains of M. ovipneumoniae associated with all‐age disease outbreaks between 1986 and 2014, a pattern consistent with repeated transmission events (spillover) from reservoir hosts. Phylogenetic analysis showed that the strain associated with the outbreak observed in this study was likely of domestic goat origin, whereas strains from other recent disease outbreaks probably originated in domestic sheep. Some strains persisted and spread across populations, whereas others faded out or were replaced. Lack of cross‐strain immunity in the face of recurrent spillovers from reservoir hosts may account for a significant proportion of the disease outbreaks in bighorn sheep that continue to happen regularly despite a century of exposure to domestic sheep and goats. Strain‐specific immunity could also complicate efforts to develop vaccines. The results of our study support existing management direction to prevent contacts that could lead to pathogen transmission from domestic small ruminants to wild sheep, even if the wild sheep have previously been exposed. Our data also show that under current management, spillover is continuing to occur, suggesting that enhanced efforts are indicated to avoid introducing new strains of M. ovipneumoniae into wild sheep populations. We recommend looking for new management approaches, such as clearing M. ovipneumoniae infection from domestic animal reservoirs in bighorn sheep range, and placing greater emphasis on existing strategies to elicit more active cooperation by the public and to increase vigilance on the part of resource managers. © 2016 The Wildlife Society.

Role of carriers in the transmission of pneumonia in bighorn sheep (Ovis canadensis)

ABSTRACTIn the absence of livestock contact, recurring lamb mortality in bighorn sheep (Ovis canadensis) populations previously exposed to pneumonia indicates the likely presence of carriers of pneumonia-causing pathogens, and possibly inadequate maternally derived immunity. To investigate this problem we commingled naïve, pregnant ewes (n=3) with previously exposed rams (n=2). Post-commingling, all ewes and lambs born to them acquired pneumonia-causing pathogens (leukotoxin-producing Pasteurellaceae and Mycoplasma ovipneumoniae), with subsequent lamb mortality between 4-9 weeks of age. Infected ewes became carriers for two subsequent years and lambs born to them succumbed to pneumonia. In another experiment, we attempted to suppress the carriage of leukotoxin-producing Pasteurellaceae by administering an antibiotic to carrier ewes, and evaluated lamb survival. Lambs born to both treatment and control ewes (n=4 each) acquired pneumonia and died. Antibody titers against leukotoxin-producing Pasteurellaceae in all eight ewes were ‘protective’ (>1:800 and no apparent respiratory disease); however their lambs were either born with comparatively low titers, or with high (but non-protective) titers that declined rapidly within 2-8 weeks of age, rendering them susceptible to fatal disease. Thus, exposure to pneumonia-causing pathogens from carrier ewes, and inadequate titers of maternally derived protective antibodies, are likely to render bighorn lambs susceptible to fatal pneumonia.

A chimeric protein comprising the immunogenic domains of Mannheimia haemolytica leukotoxin and outer membrane protein PlpE induces antibodies against leukotoxin and PlpE

Mannheimia haemolytica is a very important pathogen of pneumonia in ruminants. Bighorn sheep (BHS, Ovis canadensis) are highly susceptible to M. haemolytica-caused pneumonia which has significantly contributed to the drastic decline of bighorn sheep population in North America. Pneumonia outbreaks in wild BHS can cause mortality as high as 90%. Leukotoxin is the critical virulence factor of M. haemolytica. In a ‘proof of concept’ study, an experimental vaccine containing leukotoxin and surface antigens of M. haemolytica developed by us induced 100% protection of BHS, but required multiple booster injections. Vaccination of wild BHS is difficult. But they can be vaccinated at the time of transplantation into a new habitat. Administration of booster doses, however, is impossible. Therefore, a vaccine that does not require booster doses is necessary to immunize BHS against M. haemolytica pneumonia. Herpesviruses are ideal vectors for development of such a vaccine because of their ability to undergo latency with subsequent reactivation. As the first step towards developing a herpesvirus-vectored vaccine, we constructed a chimeric protein comprising the leukotoxin-neutralizing epitopes and the immuno-dominant epitopes of the outer membrane protein PlpE. The chimeric protein was efficiently expressed in primary BHS lung cells. The immunogenicity of the chimeric protein was evaluated in mice before inoculating BHS. Mice immunized with the chimeric protein developed antibodies against M. haemolytica leukotoxin and PlpE. More importantly, the anti-leukotoxin antibodies effectively neutralized leukotoxin-induced cytotoxicity. Taken together, these results represent the successful completion of the first step towards developing a herpesvirus-vectored vaccine for controlling M. haemolytica pneumonia in BHS, and possibly other ruminants.

Potential Foraging Decisions by a Desert Ungulate to Balance Water and Nutrient Intake in a Water-Stressed Environment.

Arid climates have unpredictable precipitation patterns, and wildlife managers often provide supplemental water to help desert ungulates endure the hottest, driest periods. When surface water is unavailable, the only source of water for ungulates comes from the forage they consume, and they must make resourceful foraging decisions to meet their requirements. We compared two desert bighorn sheep (Ovis canadensis nelsoni) populations in Arizona, USA: a treatment population with supplemental water removed during treatment, and a control population. We examined whether sheep altered their seasonal diets without supplemental water. We calculated water and nutrient intake and metabolic water production from dry matter intake and forage moisture and nitrogen content, to determine whether sheep could meet their seasonal daily water and nutrient requirements solely from forage. Diets of sheep were higher in protein (all seasons) and moisture (autumn and winter) during treatment compared to pretreatment. During treatment, sheep diet composition was similar between the treatment and control populations, which suggests, under the climatic conditions of this study, water removal did not influence sheep diets. We estimated that under drought conditions, without any surface water available (although small ephemeral potholes would contain water after rains), female and male sheep would be unable to meet their daily water requirements in all seasons, except winter, when reproductive females had a nitrogen deficit. We determined that sheep could achieve water and nutrient balances in all seasons by shifting their total diet proportions by 8–55% from lower to higher moisture and nitrogen forage species. We elucidate how seasonal forage quality and foraging decisions by desert ungulates allow them to cope with their xeric and uncertain environment, and suggest that, with the forage conditions observed in our study area during this study period, providing supplemental water during water-stressed periods may not be necessary for desert bighorn sheep.

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.

Habitat Quality in Association with Herd Health in Two Bighorn Sheep (Ovis canadensis canadensis) Populations

Habitat Quality in Association with Herd Health in Two Bighorn Sheep (Ovis canadensis canadensis) Populations

Record books do not capture population trends in horn length of bighorn sheep

Many agencies and researchers use data from harvested animals to study temporal trends in phenotype. For large mammals, complete harvest records are typically only available for the past few decades, but records of the largest trophies have been collected for over a century. To examine whether record books and data from male bighorn sheep (Ovis canadensis) harvested under a minimum-curl regulation could detect temporal trends in horn length, we simulated populations of trophy-harvested male bighorn sheep where horn length was modeled to increase, remain stable, and decrease over time. All populations experienced a simulated harvest based on a minimum horn length, but only horns in the longest 5% of the initial distribution were entered in a fictional record book. We then assessed whether monitoring of harvested and “record” males detected temporal trends. Data from selective harvest underestimated declines and initially underestimated increases, but qualitatively detected both trends. Record-book entries, however, severely underestimated increases and did not detect declines, suggesting that they should not be used to monitor population trends. When these biases are taken into account, complete trophy harvest records can provide useful biological information. © 2015 The Wildlife Society.

PSOROPTES INFESTATION AND TREATMENT IN AN ISOLATED POPULATION OF BIGHORN SHEEP (OVIS CANADENSIS).

The authors captured bighorn sheep (Ovis canadensis) comprising a small population in the San Bernardino Mountains of California and evaluated the degree of infestation by mites of the genus Psoroptes for each individual. The animals were treated with two novel methods: amitraz-impregnated collars and cyfluthrin-impregnated ear tags and recaptured the following year to evaluate the effect of treatment. The authors compared data on degree of infestation for animals recaptured in the posttreatment year, detected no significant interyear differences in infestation severity scores among animals treated with amitraz or cyfluthrin, and could not detect any differences between treatment types. However, a significant (P<0.10) decreased pattern in severity scores from the beginning to the end of treatments was detected, suggesting a cumulative therapeutic value in repeated annual treatments across the 3-yr period. Additionally, the authors detected a lower median mite severity score between 2000 and a later capture in 2006. These positive outcomes may be the result of previous treatments during 2000-2002, but environmental covariates not accounted for could have been contributing factors. Avermectin drugs with longer release profiles may be a more effective treatment option in this and other small bighorn sheep populations that are compromised with mite infestations.

Temporal dynamics of linkage disequilibrium in two populations of bighorn sheep.

Linkage disequilibrium (LD) is the nonrandom association of alleles at two markers. Patterns of LD have biological implications as well as practical ones when designing association studies or conservation programs aimed at identifying the genetic basis of fitness differences within and among populations. However, the temporal dynamics of LD in wild populations has received little empirical attention. In this study, we examined the overall extent of LD, the effect of sample size on the accuracy and precision of LD estimates, and the temporal dynamics of LD in two populations of bighorn sheep (Ovis canadensis) with different demographic histories. Using over 200 microsatellite loci, we assessed two metrics of multi-allelic LD, D′, and χ′2. We found that both populations exhibited high levels of LD, although the extent was much shorter in a native population than one that was founded via translocation, experienced a prolonged bottleneck post founding, followed by recent admixture. In addition, we observed significant variation in LD in relation to the sample size used, with small sample sizes leading to depressed estimates of the extent of LD but inflated estimates of background levels of LD. In contrast, there was not much variation in LD among yearly cross-sections within either population once sample size was accounted for. Lack of pronounced interannual variability suggests that researchers may not have to worry about interannual variation when estimating LD in a population and can instead focus on obtaining the largest sample size possible.

Sex-based differences in the adaptive value of social behavior contrasted against morphology and environment.

The adaptive nature of sociality has long been a central question in ecology and evolution. However, the relative importance of social behavior for fitness, compared to morphology and environment, remains largely unknown. We assessed the importance of sociality for fitness (lamb production and survival) in a population of mark6d bighorn sheep (Ovis canadensis) over 16 years (n = 1022 sheep-years). We constructed social networks from observations (n = 38,350) of group membership (n = 3150 groups). We then tested whether consistent individual differences in social behavior (centrality) exist and evaluated their relative importance compared to factors known to affect fitness: mass, age, parental effects, and population density. Sheep exhibited consistent individual differences in social centrality. Controlling for maternal carryover effects and age, the positive effect of centrality in a social network on adult female lamb production and survival was equal or greater than the effect of body mass or population density. Social centrality had less effect on male survival and no effect on adult male lamb production or lamb survival. Through its effect on lamb production and survival, sociality in fission-fusion animal societies may ultimately influence population dynamics equally or more than morphological or environmental effects.