Sex, size, and dependent young influence how brown bears select habitat relative to salmon streams

Abstract

To survive and reproduce, animals must balance resource acquisition with mortality avoidance and thus should maximize food intake while minimizing risk. Apex predators are unique because non-anthropogenic predation generally exists in the form of infanticide. Therefore, female apex predators with young may use sub-optimal resources to reduce risk of infanticide. Habitat use may also be driven by social dominance, where larger, more dominant individuals can exclude non-dominant individuals from prime foraging areas. Brown bears (Ursus arctos) are an apex predator, and coastal populations rely on spatially concentrated seasonal salmon (Oncorhynchus spp.). We examined how size, sex and cub age influenced brown bear habitat selection relative to salmon streams on Afognak and Raspberry islands, Alaska during salmon spawning season (1 June–15 September). We used brown bear Global Positioning Systems (GPS) locations in logistic habitat selection models to determine how presence of young and brown bear head circumference (as a proxy for dominance) affected brown bear selection of habitat near salmon streams. For males and females with young, probability of selection declined with increasing distance from salmon streams. For females with yearlings and two-year-olds, larger females selected habitat closer to streams than smaller females. For females without cubs, probability of selection increased farther from streams and the effect was stronger for smaller females than larger females. Females with cubs may prioritize energy acquisition over infanticide avoidance or may forage on less energetically optimal food farther from coasts to reduce contact with dominant males and females with older dependent young. Larger females with yearlings and two-year-olds may be more likely to compete with males for foraging opportunities in prime areas, as risk of infanticide may be lower. Brown bears use variable strategies across sex, age, and reproductive classes to acquire resources while reducing competition and risk of infanticide.