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AUTHORS: Jon S. Horne, Mark Hurley*, Scott Bergen, Kayte Groth – Idaho Department of Fish and Game
ABSTRACT: Effective management of elk (Cervus canadensis) populations is facilitated by an understanding of the factors that influence elk survival. From 2005 - 2016, we monitored elk across the state of Idaho for mortality and often times cause-specific mortality. We compiled known-fate survival data from 2,007 radio-collared elk (1,273 adult cows and 834 6-month-old calves). Statewide, lion and wolf predation were the main causes of mortality for cows (35% and 32%, respectively) and 6-month old calves (45% and 29%, respectively). Mortality rates were highly variable across elk populations and years. To examine factors potentially causing this variation, each elk was assigned to one of 29 populations based on its winter range. We then modeled risk of mortality as a function of winter severity, summer nutritional resources, and wolf abundance. For calves, we found a negative relationship between chest girth and risk of mortality and a positive relationship with wolf pack size and snow depth. For adult cows, we found a positive relationship between risk of mortality and wolf pack size and snow depth and a parabolic relationship with age. Overall, we found that elk survival is inherently complex but by utilizing a data set encompassing substantial spatial and temporal variation, we were able to identify the main drivers of elk survival in Idaho.
