抄録
Grooming episodes among adult females in a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama, Okayama Prefecture, were recorded during the non-mating periods from April to September including the birth season for four continuous years, to describe appearance, disappearance and long-term maintenance of grooming relationships in female dyads. Closely related macaque females are well known to have frequent grooming interactions with each other. The present study, however, found that grooming interactions between mothers with adult daughters and their older daughters tend to decrease with increasing age, and that in some dyads of the mother and her older daughter, no grooming interactions were finally recorded. A similar tendency was also found in sister dyads: grooming interactions between older sisters tended to decrease gradually with increasing age. On the other hand, in some unrelated female dyads, grooming interactions were observed throughout the four-year-observation period, albeit infrequently. In such unrelated female dyads, the two females were same-aged or similar-aged. When females lost their most frequent grooming partners from the group, some females newly selected their related females as the most frequent grooming partner, while others selected unrelated females. These findings indicate that females do not maintain grooming relationships with all closely related females such as daughters, and the degree to which closely related females groom each other tends to change through many years, while females may maintain grooming relationships with some unrelated females for years.
