Behavioural Variability in Macaques and Langurs of the Western Ghats, India.

Studies that compare differences in the behavioural variability across species and genera are rare among south Asian primates. Such studies are important for understanding within-group feeding competition in primates as interindividual difference in frequency of behaviour is a good indicator of feeding competition. We compared the variability in individual activities of lion-tailed macaques, bonnet macaques, Nilgiri langurs, and black-footed grey langurs. Both macaque species showed variability in their activities, with bonnet macaques showing higher variability than lion-tailed macaques. This indicated higher within-group competition in bonnet macaques than in lion-tailed macaques. Folivorous Nilgiri langurs and black-footed grey langurs did not show variability in any behaviour, indicating weak or negligible within-group competition. Except in the bonnet macaque, the interindividual differences in activities in the other species were potentially due to the differences between lactating and non-lactating females. We observed that langurs were less variable than macaques, indicating higher within-group competition in macaques than in langurs. We also observed a higher frequency of aggressive interactions during feeding among macaques than langurs, substantiating higher within-group competition in macaques than in langurs. We further discuss the different possibilities of within-group contest and scramble competition in these species.

Folivory as a Constraint on Social Behaviour of Langurs in South India.

Folivory, being a dietary constraint, can affect the social time of colobines. In the present study, we compared food items and activity budgets of two closely related species of colobines inhabiting South India, i.e. the Hanuman langur (Semnopithecus hypoleucos) and Nilgiri langur (Semnopithecus johnii), to determine whether folivory had an impact on social time in these species. Our study established that Nilgiri langurs were more folivorous than Hanuman langurs. Nilgiri langurs spent much less time on social activities, but more time on resting, although the social organization of S. hypoleucos was similar to that of the Nilgiri langur. The enforced resting time for fermentation of leafy food items may have reduced the time available for social interactions, which in turn affected the social time in Nilgiri langurs. By comparing the data from previous studies on other Hanuman langur species, we found that S. hypoleucos spent a similar amount of time on social activities as Semnopithecus entellus. Hence, the social behaviour of S. entellus and S. hypoleucos is phylogenetically highly conservative.

Male takeover and infanticide in Nilgiri langurs Semnopithecus johnii in the Western Ghats, India.

Male takeover and infanticide are a widespread phenomenon among non-human primates, observed mostly in species with a relatively longer lactation in relation to gestation. In this study, we report for the first time an episode of male takeover and infanticide, and the rarely reported occurrence of an all-male band and female dispersal, in Nilgiri langurs, Semnopithecus johnii, in the Western Ghats, India. The new male was a member of an all-male band. After the takeover, the resident male and 3 juvenile males left the group and joined the all-male band. A female whose infant was killed was found missing after some days. There were significant changes in the patterns of social interactions among the resident group females soon after the male takeover, wherein the females spent less time on social interactions as compared to before and after the episode of takeover. The new male rarely interacted with the females soon after the takeover. We also observed that the resident group shifted its home range to a poorer quality habitat.

Drastic population decline and conservation prospects of roadside dark-bellied bonnet macaques (Macaca radiata radiata) of southern India.

We carried out a survey on roadside dark-bellied bonnet macaques (Macaca radiata radiata) on the highways around the south Indian city of Mysore. The present survey was the fourth since 1989 on the same populations. We divided the habitats into intensive cultivation (IC), wet cultivation (WC), and scrub forests (SC). The number of groups has significantly reduced from 54 to 31 and the number of animals has declined from 1,207 to 697 from 1989 to 2009. This decline has been recorded only in the IC and WC areas, whereas the population in SC with places of Hindu worship has remained stable. Due to the loss of roadside Ficus trees over the years, the habitat of the monkeys has almost disappeared. Since bonnet macaque is not primarily a forest-dwelling species, the seemingly widespread primate may soon become 'threatened' if the non-forest populations continue to decline. Scrub forests in small hillocks housing Hindu temples remain the only prospective places for conservation of bonnet macaques.