Elk Group Size Research Articles

The influence of hunting pressure and ecological factors on fecal glucocorticoid metabolites in wild elk

Climate change and human population growth have increased anthropogenic threats to biodiversity and habitat fragmentation. Ecologists and conservationists need tools to assess the effect of these ecological and environmental perturbations on organismal fitness. One possibility is glucocorticoids (e.g. cortisol and corticosterone) which integrate various factors such as anthropogenic disturbances, predation, food or environmental stressors. Here we tested the hypothesis that fecal glucocorticoid metabolite concentrations (GCMs) in wild female elk Cervus canadensis increased as the hunting season progressed. We also examined the influence of year, food availability and elk group size on fecal GCMs. We found that as the hunting season progressed, fecal GCMs tended to decrease. We also found that as the number of cows in a group increased, GCMs decreased and found a strong effect of year on fecal GCMs, with samples collected in 2016 having lower fecal GCMs than those collected in 2015, 2017 and 2018. However, yearly variation was not driven by availability of hard mast forage. The association between hunting pressure and fecal GCMs and identifying what is driving yearly variation in fecal GCMs warrants further study. We highlight the negative influence of group size, possibly due to vigilance, on fecal GCMs and the importance of examining ecologically relevant covariates to accurately identify main treatment effects.

Factors affecting gray wolf (Canis lupus) encounter rate with elk (Cervus elaphus) in Yellowstone National Park

Despite encounter rates being a key component of kill rate, few studies of large carnivore predation have quantified encounter rates with prey, the factors that influence them, and the relationship between encounter rate and kill rate. The study’s primary motivation was to determine the relationship between prey density and encounter rate in understanding the mechanism behind the functional response. Elk (Cervus elaphus Linnaeus, 1758) population decline and variable weather in northern Yellowstone National Park provided an opportunity to examine how these factors influenced wolf (Canis lupus Linnaeus, 1758) encounter rates with elk. We explored how factors associated with wolf kill rate and encounter rate in other systems (season, elk density, elk group density, average elk group size, snow depth, wolf pack size, and territory size) influenced wolf–elk encounter rate in Yellowstone National Park. Elk density was the only factor significantly correlated with wolf–elk encounter rate, and we found a nonlinear density-dependent relationship that may be a mechanism for a functional response in this system. Encounter rate was correlated with number of elk killed during early winter but not late winter. Weak effects of snow depth and elk group size on encounter rate suggest that these factors influence kill rate via hunting success because kill rate is the product of hunting success and encounter rate.

Managing more than the mean: using quantile regression to identify factors related to large elk groups

Summary Animal group size distributions are often right‐skewed, whereby most groups are small, but most individuals occur in larger groups that may also disproportionately affect ecology and policy. In this case, examining covariates associated with upper quantiles of the group size distribution could facilitate better understanding and management of large animal groups.We studied wintering elk groups in Wyoming, where group sizes span several orders of magnitude, and issues of disease, predation and property damage are affected by larger group sizes. We used quantile regression to evaluate relationships between the group size distribution and variables of land use, habitat, elk density and wolf abundance to identify conditions important to larger elk groups.We recorded 1263 groups ranging from 1 to 1952 elk and found that across all quantiles of group size, group sizes were larger in open habitat and on private land, but the largest effect occurred between irrigated and non‐irrigated land [e.g. the 90th quantile group size increased by 135 elk (95% CI = 42, 227) on irrigation].Only upper quantile group sizes were positively related to broad‐scale measures of elk density and wolf abundance. For wolf abundance, this effect was greater on elk groups found in open habitats and private land than those in closed habitats or public land. If we had limited our analysis to mean or median group sizes, we would not have detected these effects. Synthesis and applications. Our analysis of elk group size distributions using quantile regression suggests that private land, irrigation, open habitat, elk density and wolf abundance can affect large elk group sizes. Thus, to manage larger groups by removal or dispersal of individuals, we recommend incentivizing hunting on private land (particularly if irrigated) during the regular and late hunting seasons, promoting tolerance of wolves on private land (if elk aggregate in these areas to avoid wolves) and creating more winter range and varied habitats. Relationships to the variables of interest also differed by quantile, highlighting the importance of using quantile regression to examine response variables more completely to uncover relationships important to conservation and management.

Effects of elk density on elk aggregation patterns and exposure to brucellosis

Increasing elk (Cervus elaphus nelsoni) populations across the West in response to increased demand for recreational and hunting opportunities may have negative, unintended consequences for disease transmission risk. Historically, free-ranging elk populations were not thought to sustain brucellosis (Brucella abortus), but recent studies suggest increasing elk densities may result in free-ranging elk serving as maintenance hosts for the disease. We evaluated spatial variation in elk density, group sizes, and adult female brucellosis seroprevalence in 39 elk management districts in the Greater Yellowstone Ecosystem using a Bayesian approach. We used modeled relationships to estimate the effects of reducing elk density by 10–90% on grouping patterns and seroprevalence rates. Reducing the density of the 3 highest density elk herds by 10%, 50%, and 90% was predicted to result in a 9%, 39%, and 59% decrease in mean group size, whereas reducing the density of the 3 lowest density elk herds was predicted to result in only a 0%, 0.7%, and 1.3% decrease in mean group size. We estimated seroprevalence rates of 0.01–0.27 across management districts, and seroprevalence increased as elk density increased. For the 7 of 39 management districts with >10% estimated seroprevalence, 10%, 50%, and 90% reductions in elk density resulted in predicted mean seroprevalence reductions of 2%, 7%, and 9%, respectively. For the 14 management districts with ≤1% estimated seroprevalence, 10%, 50%, and 90% reductions in elk density resulted in no measurable change in predicted mean seroprevalence. Our results suggest that elk density has an important effect on elk group sizes, which may influence the risk of brucellosis transmission and resultant exposure rates. Manipulating elk density may in turn affect brucellosis seroprevalence rates. However, debate among the diverse stakeholders involved in elk management on the effectiveness of reducing density, group sizes, and brucellosis exposure rates in elk, relative to other interests and objectives, is necessary prior to manipulation of elk density for this purpose. © 2015 The Wildlife Society.

Context dependence of elk (Cervus elaphus) vigilance and wolf (Canis lupus) predation risk

To assess the relationship between predation risk perceived by elk (Cervus elaphus L., 1758) as evidenced by vigilance, we conducted focal animal observations in elk winter range. We stratified our observations in Glacier National Park, Montana, USA, and Waterton Lakes National Park, Alberta, Canada, in valleys with three wolf (Canis lupus L., 1758) population levels (Saint Mary Valley: no wolf; Waterton Valley: moderate wolf; North Fork Valley: high wolf). Although the lowest elk vigilance occurred in Saint Mary and the highest in the North Fork, our analysis revealed a complex picture. Our model included distance to forest edge, group size, distance to road, social class, and impediments to detecting and escaping wolves. In Saint Mary, none of the variables were significant. In Waterton, vigilance decreased as elk group size increased (p < 0.00001) and increased as impediments increased (p = 0.0005). In the North Fork, vigilance increased as group size increased (p = 0.03), bulls were more vigilant (p = 0.02), and the interaction between group size and impediments was significant (p = 0.03). Where a high wolf population existed, elk did not exhibit uniform or expected response to predation risk factors. High wolf presence may necessitate adaptive elk behaviour that differs from response to moderate wolf presence.

Variations in elk aggregation patterns across a range of elk population sizes at Wall Creek, Montana

AbstractIn the Greater Yellowstone Ecosystem, growing concern over increasing rates of brucellosis seroprevalence in wildlife has challenged wildlife managers to develop strategies for minimizing the potential for pathogen exchange within and between wildlife populations. Recent evidence suggests that increases in elk seroprevalence may be associated with increasing elk densities and/or increasing size of elk aggregations. However, the interactions between elk population density, landscape factors, and elk aggregation patterns are not well‐understood, making appropriate management responses challenging. Using a unique, long‐term elk aggregation dataset collected across a wide range of elk population sizes, we investigated relationships between elk population size, landscape factors, and elk aggregation responses (group size and group density) with goals of clarifying how changes in elk population size may affect elk aggregation patterns. Overall, landscape attributes and weather had a stronger influence on elk aggregation patterns than factors such as elk population size that are within management control. We found little evidence that elk population size affected mean elk group sizes, but we did find evidence that the size and density of the largest elk aggregations increased as elk population size increased. We also found some evidence that group densities increased following the establishment of wolves. However, across the relatively wide range of elk population sizes observed in this study, only modest changes in elk group density were observed, suggesting that dramatic reductions in population sizes would be necessary to produce measureable reductions in elk group density to affect frequency‐dependent transmission. Management actions designed to lower disease transmission are likely to negatively affect other objectives related to elk management and conservation. We therefore suggest that a first step in managing disease transmission risk is agreement among stakeholders interested in elk management of all objectives related to elk management, including acknowledgment that disease transmission is undesirable. © 2011 The Wildlife Society.

Development of a Sightability Model for Low‐Density Elk Populations in Ontario, Canada

ABSTRACT The status of recolonizing elk (Cervus elaphus) populations in Ontario, Canada, is unclear and there is a need for effective population survey methods that can be applied locally. We sought to develop a sightability model that could account for both low densities of elk and dense forest cover in elk‐release areas in Ontario. We corrected winter aerial survey counts for sightability based on radiocollared animals known to be within observable distance of the aircraft. The multivariate model with the highest Akaike's Information Criterion corrected for sample size weight (wi = 0.427) revealed that elk group size, elk activity, dominant tree type, percent canopy cover, and percent conifer cover were significant predictors of elk sightability. The group‐size effect indicated that odds of sighting an elk increased by 1.353 (95% CI = 0.874‐3.689) for every additional elk. Standing elk were 5.033 (95% CI = 0.936‐15.541) times more likely to be observed than were resting elk, and those located in conifer cover were 0.013 (95% CI = 0.001‐0.278) times less likely to be sighted than elk in deciduous cover. Furthermore, elk located in >50% canopy cover and >50% conifer cover were 0.041 (95% CI = 0.003‐0.619) times and 0.484 (95% CI = 0.024‐9.721) times less likely to be sighted than elk in more open habitat, respectively. During model validation, observers detected 79% (113/143) of known elk in any given area, and population and sightability model predictions (±90% CI) overlapped with the population estimate, implying that our predictive model was robust. Unsurprisingly, large groups of elk in open habitat increased model precision, which highlights difficulties of counting Ontario elk in their northern range. We conclude that our model provided increased reliability for estimating elk numbers in Ontario compared to existing methods, and that the estimator may be useful in other areas where elk density is low and sightability is poor due to dense forest cover.

Modeling Elk Sightability Bias of Aerial Surveys During Winter in the Central Cascades

Aerial surveys of elk have generally not been used to estimate elk abundance in western Washington primarily due to concerns over the highly variable detectability of elk in forested vegetation. The purpose of our study was to investigate the development and application of aerial sightability models to survey elk in forested habitats of the west-central Cascades. Survey units were delineated and surveyed from a helicopter. We used radio-tagged elk and logistic regression to model the influence of vegetation cover characteristics, elk group size, and activity on sightability of elk. Models were assessed using Akaike Information Criteria. The best model included elk group size and percentage of vegetative cover. These results indicate that when corrected for sightability, aerial surveys for elk may be a reasonable alternative for assessing elk abundance in wintering elk herds of the central Cascades.

Prey Risk Allocation In A Grazing Ecosystem

Understanding the behaviorally mediated indirect effects of predators in ecosystems requires knowledge of predator-prey behavioral interactions. In predator-ungulate-plant systems, empirical research quantifying how predators affect ungulate group sizes and distribution, in the context of other influential variables, is particularly needed. The risk allocation hypothesis proposes that prey behavioral responses to predation risk depend on background frequencies of exposure to risk, and it can be used to make predictions about predator-ungulate-plant interactions. We determined non-predation variables that affect elk (Cervus elaphus) group sizes and distribution on a winter range in the Greater Yellowstone Ecosystem (GYE) using logistic and log-linear regression on surveys of 513 1-km2 areas conducted over two years. Employing model selection techniques, we evaluated risk allocation and other a priori hypotheses of elk group size and distributional responses to wolf (Canis lupus) predation risk while accounting for influential non-wolf-predation variables. We found little evidence that wolves affect elk group sizes, which were strongly influenced by habitat type and hunting by humans. Following predictions from the risk allocation hypothesis, wolves likely created a more dynamic elk distribution in areas that they frequently hunted, as elk tended to move following wolf encounters in those areas. This response should dilute elk foraging pressure on plant communities in areas where they are frequently hunted by wolves. We predict that this should decrease the spatial heterogeneity of elk impacts on grasslands in areas that wolves frequently hunt. We also predict that this should decrease browsing pressure on heavily browsed woody plant stands in certain areas, which is supported by recent research in the GYE.

Effects of elk group size on predation by wolves

Wolf-prey research has focused on single-prey systems in North America dominated by moose (Alces alces) or white-tailed deer (Odocoileus virginianus). Elk (Cervus elaphus) are social ungulates and the main prey item of wolves (Canis lupus) in Banff National Park (BNP), Alberta. Grouping behaviour may affect the functional response of predators by changing how predators encounter and kill prey. We studied wolf predation on elk in BNP during the winters of 1997–1998 and 1998–1999 and tested how elk group size affected the availability of and encounter rates with elk groups and attack success of wolves. Wolves encountered larger elk groups than expected based on availability, and killed more elk from large groups than expected based on numbers of encounters. Elk group size increased with elk density in BNP. Increased rates of encounter with and success of attacking large elk groups, and the positive group size – density relationship may be a mechanism for density-dependent predation. We developed a predation-risk model to test the prediction that grouping will benefit individual elk, given this predation regime. Elk appeared to adopt two different strategies to minimize predation risk: living in small herds that were rarely encountered by wolves or living in large herds that reduced their predation risk through dilution.

Effect of Undercounting and Model Selection on a Sightability-Adjustment Estimator for Elk

Aerial surveys of wildlife populations must correct for failure to observe all animals to obtain unbiased population estimates. We captured and radiocollared elk (Cervus elaphus) in northcentral Pennsylvania to develop a linear-logistic model of characteristics of elk groups associated with visibility bias during helicopter surveys. We used this sightability model in a Horvitz-Thompson sightability-adjustment population estimator. The number of elk in a group was positively correlated (P < 0.001), and the percent canopy cover was negatively correlated (P = 0.002) with the probability of observing a group of elk. Observations of elk groups of known size indicated that helicopter crews undercounted elk group sizes, and percentage of elk missed increased as percent canopy cover increased. Probably because of this undercounting, 3 of 6 population estimates from the sightability-adjustment estimator were less than the number of elk known to be alive on the study area. Simulations of elk surveys using our empirical data indicated that our population estimates may have been negatively biased by 20%, because of undercounting. The assumption of complete enumeration of sighted groups of animals should be verified when using this estimator. When all assumptions of the estimator were met during computer simulations, confidence intervals calculated under the assumption of asymptotic normality and log-normality did not provide nominal coverage. We found that a sightability model using only group size as an independent variable, even when the true sightability model also included percent canopy cover, provided population estimates with little negative bias (<1%), shorter confidence intervals, and the lowest mean square error (MSE). Further research is needed on selection of sightability models, and we recommend using a bootstrap technique to calculate confidence intervals. We believe the sightability-adjustment estimator is unsuitable for estimating population size for small populations (≤1,000 animals).

Relationships Between Social Group Size of Elk (Cervus elaphus) and Habitat Cover in Michigan

-We studied social group size of elk relative to vegetative cover to test the hypothesis that ungulate group sizes are inversely related to vegetative cover. Elk group sizes in Michigan did not vary inversely with cover, perhaps because of the abundant hiding cover throughout the Michigan elk range and/or the lack of predation on elk in Michigan. An inverse relationship between social group size and vegetative cover may not be typical of all ungulates in all habitats.