Embracing in a Wild Group of Yakushima Macaques (Macaca fuscata yakui) as an Example of Social Customs

Recently, some primatologists have begun studying social customs, which had been neglected in research despite their importance to human culture. We observed embracing behaviors 64 times during 543.8 hours of focal animal sampling, targeting adult females in a wild group of Japanese macaques in Yakushima, Japan, and compared the results with those in macaques in Kinkazan. Embracing occurred immediately after the spontaneous pause of allogrooming, aggressions, and approach between dyads frequently exchanging antagonistic interactions, all of which are considered to be stressful conditions. Embracing in Yakushima may, therefore, serve to reduce stress; this may also be the case in Kinkazan. Despite this functional similarity, the forms of embracing in Yakushima are slightly different from those in Kinkazan. First, not only ventro-ventral embraces, but also ventro-lateral and ventro-dorsal embraces were found in Yakushima. Second, kneading another’s fur by rhythmically opening and closing the palm occurred in Yakushima, instead of a rhythmic, body-rocking movement in Kinkazan. Because we cannot devise genetic or ecological explanations for the subtle local differences in embraces, this type of behavior may be identified as the first evidence for social customs in wild Japanese macaques.