This study reports critical changes in the behaviour patterns of lion-tailed macaques (Macaca silenus) inhabiting a continuously changing and deteriorating rain forest fragment in the Western Ghats, India. The study area, a privately owned rain forest patch in a tea/coffee garden called Puthuthotam, has suffered two massive selective logging episodes. Over the years, the native rain forest trees have been largely replaced by non-native/pioneer species resulting in loss of canopy contiguity and significant changes in other vegetation parameters. The almost wholly arboreal lion-tailed macaque now spends a considerable amount of time on the ground in this area. The species has also experienced a major shift in its diet, ranging patterns and other activities.

The lion-tailed macaque is an endangered species, and hence it is necessary that the remaining populations in the rainforests of the Western Ghats, India, be located and their habitats assessed for effective conservation. The Anaimalai Hills in the state of Tamil Nadu harbor 31 groups of lion-tailed macaques. However, the rainforest in these hills is highly fragmented. Since lion-tailed macaques are typically arboreal, the groups have become isolated. Two large rain-forest complexes in these hills harbor 12 and seven groups, respectively, and the remaining 12 groups inhabit small, isolated forest fragments. Group size ranges from six to 53 individuals, with a mean size of 16.3. In the small forest fragments, the standard deviation (SD) of group size was considerably higher than it was in the larger forest complexes. The disturbed fragments also had a higher variability in group size than the relatively undisturbed habitats. It is believed that fragmentation may impede male migration. We suggest that the fragments be managed in such a way that male migration among groups can be facilitated to overcome the potential effects of isolation.

During a 5-yr study of lion-tailed macaques in their natural habitat, we found that: 1) most births occurred from January to April (70%) and from September to December (19%), showing a bimodal pattern with a major and a minor birth peak; 2) the period of peaks remained the same over 5 yr; and 3) a similar pattern of birth peaks occurred both in groups in large forest complexes that had overlapping home ranges with other groups and in single groups that were isolated in forest fragments in the same region but with similar ecological conditions. The results suggest more of a birth seasonality than mere breeding synchronization in the wild lion-tailed macaques. We also analyzed data on births in captivity in European Zoos for 10 yr. We observed no seasonality or peaks in births, and the pattern was the same over the years. Data on rainfall suggest that resource availability in the wild habitat may not be uniform throughout the year; hence, ecological factors may play an important role in determination of birth patterns in the natural habitats of liontailed macaques.

Between-group encounters are an obvious outcome of intergroup competition. Between-group encounters in primates range from avoidance to fatally aggressive. The prevailing hypotheses explain such encounters as mate defense strategy by males and resource defense strategy by females. However, the rate and nature of between-group encounters may also be influenced by habitat and demographic characteristics. We studied the effect of forest fragment size on group encounters in lion-tailed macaques in the Western Ghats of southern India. The encounter rate decreased as the fragment size increased. Group density and home range overlap correlated positively with the encounter rate. The aggressive encounters were more in the relatively medium-sized fragment where the observed frequency of between-group encounters was higher than the expected frequency than in the small fragment and the large forest complex. Together, these results indicate a complex pattern of effects of fragment size on between-group encounters in primates.