The ecology and social organisation of Hanuman langurs (Presbytis entellus Dufresne, 1797) in Kanha tiger reserve, central Indian highlands
Hanuman langurs were studied for two years between 1980 and 1983 in Kanha Tiger Reserve, Mandla District, a 1945 sq.km tract of hilly, monsoonal, moist deciduous (sal) and dry deciduous forest, interspersed with anthropogenic meadows. Langur population density was 46.15/sq.km., 93% of troops were unimale, 69.6% of males were extra-troop (in bands), troop adult sex ratio was 1:7.9. Both gradual and rapid replacement of troop adult males occured. An all-male band attacked the study troop, killing three of six infants and, following a phase of consorting, a band male replaced the troop resident male. The observation of infanticide in a low density, undisturbed habitat supports the 'sexual selection' hypothesis and not the 'social pathology' hypothesis. Analysis of intraspecific variation suggests that troop structure and not density is associated with infant killing. The timing of takeovers with respect to the birth season agrees with that predicted if the sexual selection hypothesis is applicable. Activity, feeding and ranging budgets were estimated using scan sampling of the study troop over twelve months. Langurs selected against the use of meadow but for a clump of mixed forest at the centre of their 74.5 ha annual range. Evidence was obtained of territorial site-dependent defence. A dichotomy between troop-troop and troop-band spatial relationships is interpreted in terms of differences in male reproductive strategies and the costs and benefits of conflict. The diet was diverse, including gum and insects, but was dominated by mature leaf and fruit. Trees were not utilized in proportion to their abundance. Range patterns were related to the spatial distribution of highly selected trees and the seasonal consumption of ephemeral food items was related to their availability.