Determinations of compensatory and additive mortality have considerable implications for understanding limiting factors of a population. Although the influence of these processes is conceptually straightforward, a quantitative approach to characterize compensatory and additive mortality for large ungulates is lacking. For this study, we examined the relationship between nutritional condition entering winter, age, and cause-specific mortality for mule deer (Odocoileus hemionus) on 11 Wildlife Management Units located throughout Utah. From December 2014 to December 2018, we captured 1396 adult female mule deer using helicopter net-gunning. We fitted all deer with satellite GPS collars equipped with a 12-hour mortality censor. We attempted to locate all mortalities within 48 hours of being notified of a mortality to assign the most probable cause of death.
Results/Conclusions
From December 2014 to April 2019, we investigated 236 adult female deer that died during winter (December – April). Results indicate that ingesta-free body fat (IFBF) of adult mule deer killed by coyotes (Canis latrans) was not different from those dying of malnutrition. In contrast, mountain lions (Puma concolor) killed deer that have IFBF estimates representative of what is available in the population. When examining mortalities in relation to deer age, coyotes primarily older adults (> 8 years old), whereas cougars killed deer across all age categories in proportion to availability. Our results suggest that coyotes are killing adult deer in relatively poor condition with an increased risk of dying from other causes (i.e., malnutrition). As such, adult mortalities caused by coyote predation have a greater likelihood of being compensatory. Conversely, mountain lions are killing adult deer in better condition with higher probability of survival indicating the potential for a more additive effect.