Analysis of the Social Relations among Adolescent Males of Japanese Monkeys (Macaca fuscata fuscata) at Koshima Islet

Abstract

At the Koshima Islet, Miyazaki Prefecture, the social relations of adolescent males were studied by means of the individual tracing method for about 140 days between May 1974 and March 1975. Especially the social relations of males (6-9 years old) which had left the troop and those of males (5 years old) which had been staying in the troop were compared. The affinitive relations among adolescent males, such as grooming, following and sitting near-by or feeding on the same tree, were analyzed. The antagonistic relations among males (6-9 years old only), avoidance and agonistic interactions, were analyzed. In breeding season these interactions increased two or three times as frequently as those in non-breeding season. In the affinitive relations except following interaction the rate of consanguinities observed in the interactions decreased in breeding season in the case of when the partners were females and juveniles. While in the antagonistic relations, they decreased in breeding season when the opponents were males. Adolescent males over six years old preferred as the affinitive partner males of the same generation, females of the same generation and mothers, while they avoided strongly troop males (full adult) and adult females out of the same generation. They had agonistic interactions most frequently with the juveniles throughout the year, and only in breeding season their interactions with the troop males and adult males outside troop were frequently observed.
Five-years-old males occupied the significant stage in the developmental process in the adolescence. In non-breeding season they had affinitive relations mainly with troop members, especially their close relatives, but in breeding season they had many affinitive relations with adolescent males, especially elder brothers, outside troop. They were actually in the critical point socially where they were ready to secede from their own troop. It can be concluded that males secede from their own troop at the developmental stage from five to six years old in Koshima troop. The affinitive relations between adolescent males outside troop and the females of the same generations were conspicuous. The male-female bond in the same generation has the great significance not only as the basis on which the consort-pair will arise, but as the social channel through which males outside troop get tolerated by the troop members in breeding season. The male-bonds among adolescent males outside troop are based on three kinds of relations; i. e. the combination between brothers, the following relation between older dominant male and younger male and the grooming relation between the individuals of the same age. The author classified the social positions of males outside troop into three main types; marginal males, semi-solitary males and solitary males, and two transitional types, based on the dual criteria as to whether they have male-bonds and whether they have stable affinitive relations to troop members. These social positions are flexible in adolescent males, but they are supposed to be more rigid in full adult males.