Signals found in the grooming interactions of wild Japanese monkeys of the koshima troop

Signaling behaviors appearing in grooming interactions of wild Japanese monkeys were analysed. Vocal signals found in the grooming interactions had the content of asking the objective animal “if the vocal signaler may groom the recipient animal.” They could be divided into two categories of vocal sounds, VG-1 and VG-2. The former was uttered in common by all the troop members. The latter was uttered just before grooming by the groomer and is considered to have deeper connection with grooming. Each individual uttered mainly one kind of vocal sound out of VG-2, and the preferred vocal sounds for each individual differed. Furthermore, VG-2 differed in different troops. Behavioral signals had the content of showing “the acceptance of grooming” or showing “the request to be groomed.” The appearance of these signaling behaviors was closely related to the inter-individual relationships of grooming partners, especially as to whether or not they had blood relationships. Basically the monkeys have a system in which they must avoid each other, except in the case of mothers and their offspring, and if they had to approach too closely against this basic system, as in grooming interactions, there appeared signaling behaviors as mentioned above.