The social organization of forest hanuman langurs(Presbytis entellus)

Abstract

The social organization of hanuman langurs (Presbytis entellus;Colobinae) was studied in Kanha Tiger Reserve, Central Indian Highlands, for 2300 hr (1980–1985), in a mosaic of moist deciduous forest and anthropogenic meadow. The langur population density was 46.15/km2 and the mean troop and band sizes were 21.7 and 14.0, respectively. Of 14 troops, 13 were one-male and 1 was trimale. The population adult sex ratio was 1:2.5. The majority of female sexual solicitations was directed toward the harem male. The birth season was December to May, with an estimated gestation of 171–224 days. A review of langur reproductive seasonality suggests that breeding throughout the year is confined to those populations able to exploit human food sources. Mortality during the first year of life was 40%, including infanticide. A significant positive correlation was found between the age of an infant at death or disappearance and the mother’s subsequent interbirth interval. Five cases of social change are described, including female transfer, one-male to multimale change, troop formation, and gradual and rapid replacement of troop males. Takeover-associated infant killing by band males, in an undisturbed moderate-density population, supported the sexual-selection/infanticide hypothesis but not the social-pathology hypothesis. However, it could not be directly confirmed that an invading infanticidal male gains a reproductive advantage. The male tenure of harems was estimated to be 45 months.