Influence of habitat conditions on group size, social organization, and birth pattern of golden langur (Trachypithecus geei).

We studied endangered golden langurs in fragmented and altered habitats to understand the consequences of habitat conditions on group size, social organization, and birth seasonality. We selected 12 groups inhabiting forest edge and forest core of Chakrashila Wildlife Sanctuary (henceforth Chakrashila WLS) and adjoining the Abhaya rubber plantation. Each group was monitored every month from May 2013 to September 2016 and recorded the age-sex of individuals in the group. The births were recorded with the individual identity of females in five focal groups. The overall group size of golden langur was 11.3 ± 3.5, and ranged between 5 and 18. The mean group size in forest core, forest edge, and rubber plantation differed significantly. We recorded a total of 46 births in 12 groups across the three different habitats. The number of infants correlates positively with adult females and group size across all the 12 groups for all the years. The number of births that occurred in all the months varied significantly across the months. Births occurred in all the months but peaked between May and September (82.6%). The mean number of births positively correlated with mean monthly rainfall. Mean inter-birth interval was 24.5 ± 1.6 months that did not vary between the females. It therefore appears that group size is sensitive to forest type, and births are positively related to social and environmental factors. The behavioral parameters may influence life-history traits if continuous habitat alteration persists.