Splitting in Presbytis entellusgroups

Abstract

Four bisexual groups (three multimale and one unimale) of Presbytis entellus were observed from September, 1985 to April, 1987. The multimale groups were found at areas where there was high density of monkeys as compared to area where the unimale group was found. These four groups split only after a takeover by a member of an all-male group. Each of the three multimale groups divided into one unimale and one all-male group. The all-male groups which caused these splits left the area after one of their members took over the bisexual group. The all-male groups which were formed due to division of multimale groups remained in the same area. The split in the unimale group was again caused by interaction with an all-male group and resulted in the formation of two unimale groups; the younger females went with a new male and the older females remained with their original male. The splitting coincided with mating periods. The splitting of multimale groups took less time as compared to the splitting of the unimale group. The details of the splitting process are described. The present observations support Hrdy' s hypothesis (1977a) that Presbytis entellus maintain a unimale grouping and that the groups undergo three stages of development which turn them into age-graded multimale groups, followed by a split which returns them to unimale grouping.