The overlap of sympatric sun bears and Asiatic black bears in space and time

Sun bears and Asiatic black bears are sympatric throughout mainland Southeast Asia and share similar habitat preferences and food habits, but the spatial and temporal scales at which they manage this close coexistence are unexplored. We used two-species occupancy modeling and temporal analysis to examine fine-scale spatio-temporal overlap between these two species using baited camera traps in three sites in Thailand, including one at the extreme southern end of the black bear’s global range. Probability of occupancy by black bears was 17–22% higher than sun bears in the two northern sites (Khao Yai, Thap Lan), whereas sun bears had 6% higher occupancy in the southern-most site (Khlong Saeng). However, at all sites, occupancy and detectability of sun bear in the presence and absence of black bear were similar, and the species interaction factor was indicative of independent behavior. Sun bears and black bears had similar activity peaks as well, at dusk and dawn, across all sites. However, at the two northern sites, there were small but statistically significant differences, with the morning activity peak of sun bears shifted about two hours after that of black bears. This seemingly slight shift might help sun bears avoid black bears—but it emerges only where sun bears are outnumbered by their larger competitors (and chance of encounter thus particularly high). Our study presents one of the finest-scale investigations (daily occupancy occasions and hourly activity periods) of coexistence of sun bears and black bears and extends our understanding of the remarkably high degree of ecological overlap shared by these two bear species in nature.