Flexibility in female spatiotemporal behavioral tactics to counter infanticide risk during the mating season.

Background: Parental care is exclusively provided by females in most mammals, and mothers use several spatiotemporal behavioral tactics to minimize risks to offspring and to enhance fitness of both the mother and offspring. In species with infanticide and varying maternal care duration, dependent offspring remain vulnerable to male infanticide until separation from the mother. However, extending maternal care likely results in parent-offspring conflicts. We investigated the spatiotemporal behavioral tactics of lone female brown bears and mothers accompanied by offspring of varying ages in relation to infanticide risk and offspring separation during the mating season.

Methods: We used data from 144 individuals (92 females and 52 males, 2003-2022) to characterize female spatiotemporal behavioral responses to males during the mating season by contrasting home range and encounter area sizes, proximity to males, and dyadic associations in relation to female reproductive status. We investigated the spatiotemporal behavioral responses of mothers from a socio-spatial perspective by connecting large-scale movement behavior (home range and overlap) and small-scale social behavior (proximity and associations) of adult females and males.

Results: We found that females with dependent offspring of any age avoided males during the mating season. In comparison, lone females or mothers that lost or separated from their offspring during the mating season used larger areas and moved in closer proximity to males. The home range of mothers that remained with their offspring still largely overlapped with male home ranges, however, they did not associate (< 100 m) with males. Additionally, mothers with yearlings had similar sized home ranges as solitary females, but larger home ranges in comparison to mothers with cubs-of-the-year. This suggests that mothers with yearlings are more conspicuous on the landscape which may result in a higher detectability by males.

Conclusion: Our results suggest that mothers with offspring of any age perceive adult males as potential source of infanticide and use spatiotemporal avoidance tactics. Generally, family groups had high home range overlap with adult males, but family groups that remained together throughout the mating season did not associate with any adult male. Mothers with yearlings used larger areas in comparison to mothers with cubs, potentially indicating their increasing energetic needs. The use of spatiotemporal behavioral tactics to avoid infanticide by females with dependent offspring irrespective of age likely disrupts movement, mating, and social dynamics and on the long-term potentially increases the risk of infanticide to older offspring.