Social relationships of male Japanese macaques (Macaca fuscata) in different habitats:: a comparison between Yakushima island and Shimokita peninsula populations

Wild troops of the Japanese macaque (Macaca fuscata) live in various habitats within the Japanese archipelago. The social relationships of males can be elucidated through intraspecific comparisons of social conditions between populations of different habitats. Previous research has shown that males associate with one another more frequently on Yakushima island than on Kinkazan island, whereas male-female and female-female relationships did not differ between populations that occupy the two different habitats. However, this study did not compare the social relationships of males between habitats during the mating season, when males are expected to compete for fertile females more aggressively within and between troops. The present study compared male behavior in Yakushima island and the Shimokita peninsula populations during the mating season and found that males exchanged affiliative behaviors with one another more frequently on Yakushima island. The socionomic sex ratio (SSR: adult males/adult females) was higher in the Yakushima island troop, and this troop was involved in inter-troop encounters more frequently. In Yakushima island, more non-troop males were observed around the troop and were frequently involved in agonistic interactions with troop males. Yakushima island troop males are likely to affiliate with one another to reduce tension among themselves, in order to cooperatively attack neighboring troops and non-troop males that appear to copulate with fertile females.