Immature male and adult male interactions in bisexual langur (Presbytis entellus) troops.

One bisexual troop of langurs (Presbytis entellus) was intensively investigated for 32 months at the Junbesi-Ringmo study site in Nepal. Observations occurred during three separate studies and span a period of 6 years. All members of the study troop could be individually recognized throughout the three studies. During this investigation data were collected on immature male (from birth to 5 years of age) social relations with adult males. Social relations between these two classes of males varied both in type and in frequency of behaviors displayed. During the first study, when the troop was predominantly multi-male, young males directed various tense behaviors toward adult males. Monthly rates of occurrence of such behaviors fluctuated and showed a positive correlation with rates of agonistic behaviors between adult males. In contrast, interactions between the adult and immature males were considerably more relaxed during the second and third studies when the troop had but 1 adult male. Based on the results of these studies, and data evaluated from other studies of P. entellus, it is hypothesized that the frequency and patterning of interactions between adult males affect adult male relations with young males.