Behavioural interactions between sika deer and Japanese serows: are larger and gregarious ungulates dominant?

In ungulate assemblages, although interspecific differences in body size and gregariousness are thought to have a direct impact on winning or losing in interference competition, this has not been fully investigated. We observed a total of 64 instances of interspecific contact between larger-gregarious sika deer and smaller-solitary Japanese serows over eight years field observations. Deer-to-serow aggression were never observed. Whereas, serows showed antagonistic behaviour, such as walk push and chasing, to deer, but could rarely displace deer. Serows showed higher alertness to deer than deer did to serows. These results suggest that larger-gregarious ungulates do not necessarily exclude smaller-solitary ones and serows are sensitive to the presence of deer. Differences in aggressiveness and alertness between deer and serows may reflect differences in territoriality: serows may be more sensitive to the invasion of deer into their territory. Serows’ sensitivity to deer may have a negative effect on their population.