Risky behavior of Asian black bears differs between sex and season in a landscape fragmented by roads

Understanding the trade-off between resource acquisition and risk avoidance is crucial in behavioral ecology. Differences in parental investment and reproductive success between males and females can result in intersexual variations in the trade-off between resource acquisition and risk-taking. Roads, a major cause of habitat fragmentation, pose significant mortality risks to animals. We investigated the sex and seasonal differences in road-crossing behavior and home ranges of Asian black bears (Ursus thibetanus), as an example of risk-taking behavior of mammals in a fragmented landscape, in the Ashio-Nikko Mountains, Japan, from 2005 to 2023. Using GPS relocation data, we analyzed the frequency of road crossings and home range sizes and applied integrated step selection analysis to assess road-crossing avoidance in relation to sex, season, road type, and time of day. Bears generally avoided crossing roads, indicating that roads act as movement barriers. During the mating season, males crossed all types of roads and had larger home ranges, whereas females did not cross main and minor roads. During the hyperphagia season, both sexes crossed all road types and had larger home ranges compared to the mating season. Our findings suggest that sex- and season-specific risk-taking behavior of bears relates to mate and food acquisition: males take more risks to search for mates during the mating season compared to females. Bears crossed gated minor roads most frequently, followed by minor roads and main roads, with crossings occurring more often at night than during the day across all road types. These results suggest bears perceive and respond differently to risks of roads, which are linked to the level of human activity.