Annual elk calf survival in a multiple carnivore system

Abstract

The realized effect of multiple carnivores on juvenile ungulate recruitment may depend on the carnivore assemblage as well as compensation from forage and winter weather severity, which may mediate juvenile vulnerability to predation in ungulates. We used a time-to-event approach to test for the effects of risk factors on annual elk (Cervus canadensis) calf survival and to estimate cause-specific mortality rates for 2 elk populations in adjacent study areas in the southern Bitterroot Valley, Montana, USA, during 2011-2014. We captured and radio-tagged 286 elk calves: 226 neonates, and 60 6-month-old calves. Summer survival probability was less variable than winter (P ¼ 0.12) and averaged 0.55 (95% CI ¼ 0.47-0.63), whereas winter survival varied more than summer and significantly across study years (P ¼ 0.003) and averaged 0.73 (95% CI ¼ 0.64-0.81). During summer, elk calf survival increased with biomass of preferred forage biomass, and was slightly lower following winters with high precipitation; exposure to mountain lion (Puma concolor) predation risk was unimportant. In contrast, during winter, we found that exposure to mountain lion predation risk influenced survival, with a weak negative effect of winter precipitation. We found no evidence that forage availability or winter weather severity mediated vulnerability to mountain lion predation risk in summer or winter (e.g., an interaction), indicating that the effect of mountain lion predation was constant regardless of spatial variation in forage or weather. Mountain lions dominated known causes of elk calf mortality in summer and winter, with estimated cause-specific mortality rates of 0.14 (95% CI ¼ 0.09-0.20) and 0.12 (95% CI ¼ 0.07-0.18), respectively. The effect of carnivores on juvenile ungulate recruitment varies across ecological systems depending on relative carnivore densities. Mountain lions may be the most important carnivore for ungulates, especially where grizzly bears (Ursus arctos) and wolves (Canis lupus) are rare or recovering. Finally, managers may need to reduce adult female harvest of elk as carnivores recolonize to balance carnivore and ungulate management objectives, especially in less productive habitats for elk.

Roles of maternal condition and predation in survival of juvenile Elk in Oregon

“…At the conclusion of simulations, Clark () regressed effects of covariates against estimated population growth rates to determine the relative effect, measured by the slope and fit of the regression, for each covariate and vital rate on elk population growth rates. Similar to Eacker et al () and Lehman et al (), Clark () found that at the higher cougar densities observed in our study (>4 cougars/100 km 2 ), their predation on juvenile elk was sufficient to lower survival to a point that elk populations would decline, even in the absence of hunting adult female elk. However, in cases with lower cougar densities, elk populations would still increase under mean environmental conditions.…”

“…However, in cases with lower cougar densities, elk populations would still increase under mean environmental conditions. The results of Raithel et al (), Clark (), and Eacker et al () suggest that factors influencing juvenile survival, either through predation or nutritional pathways (i.e., birth date) in the case of our study, are having the greatest effect on elk population dynamics. Given the diversity of factors we observed influencing elk populations in our study areas, we discuss our results with respect to individual factors (climatic, bottom‐up, and top‐down), and then how these factors may be interacting to influence juvenile recruitment.…”

Landscape‐scale habitat characteristics and neonatal white‐tailed deer survival

“…For neonates found through the use of a VIT that was not expelled prematurely, date of birth was the date the VIT was expelled (Bishop et al , Hasapes and Comer ). We estimated birth mass by regressing neonate mass at capture (nearest 0.01 kg) on age at capture separately for each study area and sex, and used the estimated regression coefficients to predict birth mass (Smith et al , Eacker et al ).…”

Assessing the importance of demographic parameters for population dynamics using Bayesian integrated population modeling

“…To maintain an adequate sample of radio‐marked calves, we captured them just after birth as neonates and as 6‐month‐olds during winter (see Eacker et al. for details). Adult female elk were captured and equipped with Global Positioning System (GPS) collars during the late fall (November–December) and late winter (February).…”

“…, Eacker et al. ), which allowed us to estimate mortality due to human harvest. None of our radio‐marked adult females and only one calf elk died of human harvest during the monitoring period (2011–2014), thus losses due to human harvest were captured in our survival estimate given that our sample of radio‐marked elk were available for harvest in the study area.…”