Group fission in free-ranging rhesus monkeys of Tughlaqabad,Northern India

A population of rhesus monkeys (Macaca mulatta)at Tughlaqabad on the southeastern outskirts of New Delhi has grown rapidly in the past 4 years, and the largest group (Group A) has given rise to three smaller groups. Fissioning, or new group formation, was not consistently associated with any particular season of the year or stage of the reproductive cycle, but it did occur in each case when the parent group reached approximately 120 monkeys. The fissioning process was not preceded or accompanied by unusual aggressive behavior. It occurred quietly and appeared to be a loss of cohesion within the large group by which a subgroup achieved behavioral and spatial independence. Some aggressive interactions did occur following each fission when the new group approached or attempted to reenter the parent group. Each newly formed group was subordinate to the parent group and all other groups in the population.