How Size and Condition Influence Survival and Cause‐Specific Mortality of Female Elk

Abstract

The size of animal populations fluctuates with number of births, rate of immigration, rate of emigration, and number of deaths. For many ungulate populations, adult female survival is the most important factor influencing population growth. Therefore, increased understanding of survival and causes of mortality for adult females is fundamental for conservation and management. The objectives of our study were to quantify survival rates of female elk (Cervus canadensis) and determine cause‐specific mortality. We predicted that hunter harvest would be the leading cause of mortality. Further, we predicted that hunters would harvest animals that were in prime age (2–9 yr) and in better condition than elk predated by mountain lions (Puma concolor). From 2015 to 2017, we captured 376 female elk in central Utah, USA. We assessed body size and condition of captured elk, fitted each animal with a global positioning system‐collar, and determined cause of death when we received mortality signals. We estimated survival using Kaplan‐Meier estimates and Cox proportional hazard models within an Akaike's Information Criterion model selection framework to identify covariates that influenced survival. We analyzed differences in size and condition measurements between harvested elk and predated elk using analysis of variance tests. Our best model indicated consistent survival across years; mean survival was 78.3 ± 3.5% (SE) including hunter harvest and 95.5 ± 1.7% without hunter harvest. In decreasing order of importance, elk mortality occurred from hunter harvest (21.2%), mountain lion predation (3.7%), depredation removal (0.5%), automobile collision (0.3%), disease (0.3%), complications during calving (0.3%), and those characterized as undetermined (1.3%). Neck circumference and body length were negatively associated with survival, suggesting that larger animals in good condition had lower survival as a result of hunter harvest. Individuals that died because of cougar predation were smaller and had less loin muscle than the average animal. Hunters removed large, healthy, prime‐aged females, individuals that likely have a greater effect on population growth than elk lost to other predators. If the proportion of larger, healthy females in the population begins to decline, hunting practices may require adjustment because hunters may be removing individuals with the greatest reproductive value. © 2021 The Wildlife Society.

Migration, movements, and survival in a partially migratory elk (Cervus canadensis) population

“…In the East Kootenay Trench studies, human-caused mortalities (65% of all known mortalities; n = 26) were nearly double non-human-caused mortalities (35%); in contrast to our findings, much of the human-caused mortality in the Trench was due to hunting which resulted from the then more liberal harvest regulations (Phillips & Szkorupa, 2011). During cow harvests, hunters may target large, healthy, prime-aged females with the greatest reproductive value, which will likely have a disproportionate effect on population growth (Sergeyev et al, 2021).…”

Reducing the refuge effect: using private‐land hunting to mitigate issues with hunter access

“…), and higher elevations characterized by mountain brush species, aspen ( Populus tremuloides ), white fir ( Abies concolor ), and subalpine fir ( Abies lasiocarpa ; U.S. Forest Service 1974). Dominant mammalian fauna in the area includes several ungulate species such as elk, moose ( Alces alces ), and bighorn sheep ( Ovis canadensis ), and carnivores such as mountain lions ( Puma concolor ), coyotes ( Canis latrans ), and bobcats ( Lynx rufus ; Sergeyev et al 2021).…”

Estimating age of mule deer in the field: Can we move beyond broad age categories?

“…These parameters can inform models of population change by indicating increases, decreases, or constant rates associated with each parameter, thereby improving understanding of the drivers of population dynamics [5]. Additionally, wildlife managers rely on accurate data and models to inform management decisions such as determining the number of annual hunting permits [6,7].…”