Effects of calf predation and nutrition on elk vital rates.

ABSTRACT: Demographic data indicated a population of elk (Cervus canadensis) in northern New Mexico had reduced juvenile recruitment, resulting in a concern over quality hunting opportunities. Following several years of low calf:female ratios of <25:100, we conducted a 4‐year study from 2009–2012 to identify reasons for poor recruitment and evaluated the role of predation and nutrition in limiting productivity. We captured and fixed ear‐tag radio transmitters to 245 elk calves (126 males, 119 females) to determine cause‐specific mortality and estimate calf survival. During the second half of our study, we implemented a new spring black bear (Ursus americanus) season resulting in higher spring black bear harvest and evaluated response in calf survival. We also quantified herd‐wide nutritional condition and productivity. We estimated percent ingesta‐free body fat (IFBF) and pregnancy rates by sampling 1,808 hunter‐harvested female elk from autumn through winter. The primary cause of summer mortality for calves across all years was black bear predation. Estimates for annual calf survival were greater when spring black bear harvest was moderate to high (0.44–0.47) compared to periods with lower bear harvest (0.33–0.35). For every additional bear harvested in spring, radio‐tagged elk calves were 2.4% more likely to survive the summer. Across years and age classes 82 ± 1% (SE) of females were pregnant. Pregnancy rate was greatest for prime‐aged (2–14 yr) females (88 ± 1%). Our herd‐wide estimate of IFBF for prime‐aged adult female elk was 11.9 ± 0.19% but varied by pregnancy and lactation status. Our results that black bear predation was the primary cause of summer calf mortality and that adult females were in adequate nutritional condition suggested that black bear predation was limiting population productivity. Additionally, calf survival was higher in drought years, the same years when targeted spring black bear harvest was implemented. Our results demonstrated that productivity could be increased by implementing a spring black bear harvest strategy targeted around calving areas and could be applied in other areas experiencing low elk calf survival. © 2018 The Wildlife Society. [ABSTRACT FROM AUTHOR]