Factors influencing population dynamics of ungulates vary across space and in time (Sinclaire 1985, Hunter and Price 1992, Hopcraft et al. 2010). Populations of ungulates can be regulated by predation (top-down), resource availability (bottom-up), or a combination of both predation and resource availability (Ballard et al. 2001, Bishop et al. 2009, Griffin et al. 2011, Hopcraft et al. 2010). In Utah, we have observed evidence of top-down regulation for some populations (e.g., South Manti mule deer) where predation by mountain lions on adult females has limited growth (UDWR unpublished data). We have also documented evidence of resource limitation in some populations (e.g., Book Cliffs elk) where condition of females was poor and pregnancy rates low during drought years (UDWR unpublished data). In some situations, we see evidence that the relative influence of bottom-up versus top-down factors can change over relatively short time intervals in response to environmental conditions and density of both predator and prey species (sensu Hopcraft et al. 2010). Understanding predator-prey dynamics is paramount to understanding population dynamics of ungulates, but that understanding is complicated in systems with multiple predators and alternate sources of prey for those predators. Predation can be considered additive or compensatory for ungulates depending on the individual characteristics (e.g., age, condition, sex) of animals that are preyed upon. Recent work in Utah, for example, shows that coyote predation on adult mule deer is likely compensatory because coyotes select older animals in relatively poor condition (Hersey et al. unpublished data). Conversely, cougars appear to select adult mule deer in Utah in proportion to availability relative to their age and condition and thus have more potential to influence survival rates for this cohort in an additive way compared to coyotes (Hersey et al. unpublished data). The relative influence of different predators on ungulate populations likely also varies seasonally with presence of young animals or availability of carcasses for scavenging. Cougars, for example, have been shown to strongly select for neonatal elk during summer in some systems (Clark et al. 2014). Young ungulates are also typically easier to catch and process by a host of predators that typically have only limited success preying on adults. Consequently, the influence of predation on ungulate populations may manifest differentially across cohorts. For predators that also scavenge, disease events, harvest of ungulates by hunters, and winter conditions that lead to large numbers of carcasses provide resources that may further influence predation rates on ungulates. Although many predators show seasonal variation in kill rates, the amount of scavenging that occurs across taxa is unclear. Predators may also influence prey populations indirectly. These indirect effects of predators are often cryptic and more difficult to identify than direct effects (e.g., kill rates). Indirect effects include altered space use or a perceived landscape of fear, greater time spent being vigilant resulting in less time available for other activities such as foraging, and the potential for apparent competition. Apparent competition occurs when individuals from two separate species affect each other indirectly by being prey for the same predator species. For example, the presence of elk (particularly calves; Clark et al. 2014) on the landscape may increase prey availability for the predator community resulting in an increase in abundance of the predator population (e.g., cougars). If cougars have a preference for deer, for example, the presence of elk on the landscape may have a negative effect on the deer population beyond competition for food or space resources mediated through an increase in the abundance of the cougar population. To examine apparent competition, one needs to examine food habits and food preferences of the predator population, which is occurring along the Wasatch Front of Utah, in addition to understanding condition, survival, and cause-specific mortality of the various cohorts of ungulates that are prey for predators. The recently completed project on the Book Cliffs attempted to evaluate the relative role of condition and predation on population growth of elk and mule deer, but adult females for both species were in relatively poor condition due to long-term drought and limited availability of summer range, and thus those populations appeared primarily to be limited by bottom-up forces. Consequently, there is a need to assess the influence of bottom-up versus top-down effects on elk and mule deer in an area with more abundant and better-quality habitat where ungulates are healthy. Recent capture of mule deer on the Nebo unit (December of 2021) showed healthy mule deer (average Ingesta Free Body Fat [IFBF] was 12.67 percent which represented the 2nd highest point estimate for any herd-unit in 2021). Abundant summer habitat at higher elevations coupled with recent fires (e.g., Pole Creek Fire) may have contributed to such high measurements of IFBF. This scenario provides additional opportunities to learn about the relative influence of predation (top-down) versus habitat quality (bottom-up) on population dynamics of ungulates.

Because of landscape juxtaposition (e.g., relatively productive habitat) and timing (e.g., relative to the current Wasatch Front cougar study, recent Pole Creek fire, and recent increases in understanding derived from the Statewide, Book Cliffs, Cache, South Manti studies and monitoring) the Central Mountains Nebo Unit provides a unique and rare opportunity to better understand factors that drive population dynamics of ungulates. The objective of this project is to determine the relative influence of top-down (predation) vs bottom-up (habitat quality) characteristics on the population dynamics of elk and mule deer in a system that appears to have relatively high-quality summer and winter range. More specifically, we propose to examine health of adult ungulates, rates of pregnancy, production of offspring, and the survival and cause-specific mortality of neonate, juvenile, and adult mule deer and elk. In addition, we will examine resource selection and associated measures of health by deer and elk relative to space use by predators (e.g., cougars) and stochastic events that potentially influence habitat quality (e.g., fire and weather) at time scales ranging from hours to years. Results from this study will be compared to results from previous studies (e.g., the Book Cliffs comprised of relatively marginal habitat that limits herd health, the South Manti study that illustrated the factor likely limiting mule deer was predation, etc.) to better understand the population ecology of mule deer and elk throughout the entire region. The results from this study will lead to more informed decision making and better management/conservation of our big game resources across the entire state of Utah.

Nebo Unit.

This project will help determine survival and limiting factors for deer and elk on the Nebo. Statewide and unit management plans both call for monitoring of these parameters. Additionally, the cougar management plan calls for DWR to be responsive with predator management to help prey populations. This project will provide valuable data and management recommendations to improve both predator and prey management.

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The study will take place in the Central Mountains Nebo Management Unit in central Utah. To determine the effects of habitat quality on nutritional condition of adult mule deer, we will randomly capture adult deer (stratified among 3 winter range locations in the Central Mountains Nebo) in December and March of each year to assess body condition coming into winter (a function of summer habitat quality) and condition leaving winter (a function of winter habitat quality). Body condition will be determined by estimating percent body fat based on a proven combination of palpation and ultrasonography measures (Cook et al. 2007). Because elk have greater nutritional inertia (e.g., less affected by winter severity), adult elk will be captured only once during February or early March to assess body condition. Body condition data will be compared with data collected on units from around Utah which has proven informative for biologists and managers. We will fit each captured individual with a GPS collar to determine space-use patterns, estimate survival, and determine probable cause of death. By knowing the exact location of deer and elk during the entire year, we anticipate using these locations in a resource selection framework (RSF) to evaluate relative seasonal and annual selection for habitat types across the entire study area at both 2nd and 3rd order selection scales (Johnson 1980). Moreover, by recapturing previously GPS-collared animals, we will be able to link habitat use/selection to body condition providing an improved understanding how habitat treatments (e.g., Pole Creek fire) influence nutritional condition and subsequent production and survival. By recovering deceased animals within 48 hours of notice of death, these collars also will enable the determination of survival and cause-specific mortality. We will use model selection and either known-fate models in Program MARK (White and Burnham 1999) or Cox proportional hazards models to estimate seasonal and annual survival rates and examine the influence of body condition (see below), habitat use, movement patterns, and environmental conditions on these rates. To examine herd production and recruitment, we will determine pregnancy rates of adult females and survival of neonate animals. During March captures, all pregnant adults will be fitted with vaginal implant transmitters (VITs; Bishop et al. 2007). These VITs will allow us to capture and collar neonates in spring to estimate survival, recruitment, and cause-specific mortality of this under-studied age class. Neonate deer and elk collars will be supplemented by recapturing 6-month old fawns in December to estimate recruitment to 1.5 years old. Recapturing animals captured as neonates will also allow us to evaluate how habitat use influences growth rate from 0-6 months and overwinter survival. This project was be initiated in January 2023 and will be completed in June 2026. Funding is requested for FY23-FY26. This project will be conducted in conjunction with the Mammals program, which will provide funding and resources for cougar capture and collaring from fall 2021 through winter 2025 as part of the Wasatch Front cougar project. Incorporating data from 20+ GPS-collared cougars into this project will enable us to incorporate cougar habitat use and prey selection into our models to help determine what is driving ungulate populations. Ungulate captures will be conducted by the DWR contracted capture company using standard net-gunning techniques. Adult mule deer will be transported back to a staging area for processing by UDWR employees/volunteers. Data collected from the animal will include age, sex, various body measurements, blood samples, reproductive condition, and body condition (Cook et al. 2010). All animals will be processed as quickly as possible and released at the staging area. We will follow similar procedures for elk, except biologists will be transported to the captured animals.

Animals will be monitored using satellite GPS collars

This project will be a partnership between UDWR, BYU, and conservation organizations.

Results from this study will be used to improve management of deer, elk, and cougars across Utah.

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