Influence of maternal body size, condition, and age on recruitment of four brown bear populations

Abstract

Recruitment of brown bear (Ursus arctos) offspring into a population is the product of initial cub production and subsequent survival and is a critical component of overall population status and trend. We investigated the relationship between maternal body size, body condition, and age (as a surrogate for gained experience) and recruitment of dependent offspring (≥1 yr old) in 4 Alaska, USA (2014-2017), brown bear populations using logistic regression. Body size alone was our top predictor of the presence of offspring and appeared in all top models. Our data suggest that bear size is the primary driver of productivity across all 4 study populations, with larger bears having a greater chance of being observed with offspring. The effect of body condition was likely confounded by the increased energetic costs of supporting cubs through time and had a negative relationship with recruitment. Age (experience) was positively related to recruitment. Understanding the relative importance of body size, body condition, and age on the recruitment of offspring provides insights into life-history trade-offs female bears must manage as they strive to meet the nutritional costs of cub production and rearing, while minimizing risks to themselves and their offspring. Further assessment of long-term longitudinal studies of brown bears that assess the lifetime reproductive output of individuals would be highly informative to further assess the effect of experience on recruitment and to support the management of brown bear populations for recovery, conservation, sustained yield, and ecosystem function.