Rick Heeres, University of South-Eastern Norway

Dominance hierarchies in mammals are commonly established through physical confrontation, body size, the size of weapons or ornaments, or experience. The ability to win such contests is often linked to age, as individuals typically require several years to accumulate experience and to attain a competitive body size, ornamentation, or experience. In brown bears, dominance hierarchies have been documented around clumped or seasonally abundant food resources, such as salmon streams and garbage dumps. However, in populations lacking such concentrated food sources, male dominance hierarchies have only been hypothesized. In this study, we aimed to investigate male-male encounters and determine if individuals would respond differently, shifts in space-use, based on their individual characteristics (age and size difference) and during certain seasons (mating vs non-mating). We identified 62 encounters including 27 unique male brown bears between 2008-2015. To evaluate whether these encounters provide evidence for a dominance hierarchy, we calculated the change in each individual’s home range centroid before and after encounters. We calculated the shift for various temporal windows (1-day, 2-day, 3-day) before and after encounters. We then analysed whether the magnitude of these shifts was associated with differences in age and body size between the two males, as well as with the season. The results indicate that smaller and younger males have larger home range centroid shifts compared to larger and older males. This effect was only detectable within the 1-day time window, suggesting that subdominant males may respond immediately but not over longer periods. We found no evidence that seasonal context influenced the magnitude of the response. Our results suggest the presence of a male dominance hierarchy in our study population. Yet, interpretation must be made with caution, as our study population is subject to harvest management which may obscure dominance patterns.