Comparative Behavioral Ecology of All-Male and Bisexual Groups of White-Headed Langurs in Fragmented Limestone Habitats.

Objectives: Male individuals of primate species with polygynous mating usually spend part of their lives alone or join all-male groups. However, quantitative data and focused investigations on the behavioral ecology of solitary male individuals or all-male groups are limited. White-headed langurs (Trachypithecus leucocephalus) live in small groups, with one-male bisexual groups as the basic social unit. Males leave their natal group at approximately 3 years of age and live as solitary individuals or join all-male groups. In this study, we compared the differences in diet, time budget, and ranging behavior between the all-male and bisexual groups of the white-headed langur within a highly fragmented limestone habitat in the Chongzuo White-headed Langur National Nature Reserve. Based on differences in competitive ability between the all-male and bisexual group males, we predicted that the all-male group would consume more low-quality foods, spend more time feeding and moving, and occupy a larger home range than the bisexual group.

Materials And Methods: We collected behavioral data on the diet and activity budgets of one all-male and two bisexual groups from August 2007 to July 2008 using 5-min scan sampling followed by 10 min of inactivity. When an individual was feeding, we recorded the plant species and parts consumed. The locations of the focal groups were recorded every 30 min. We measured the straight-line distances between successive chronological locations throughout the day to determine the daily path length.

Results: The behavior of the all-male group differed from that of the bisexual group, with the all-male group consuming more mature leaves, increasing feeding, having a larger home range, and longer daily path lengths. However, the behavior of the all-male group did not differ from that of another bisexual group that had a large overlapping area with the all-male group.

Discussion: Our results partially documented that the all-male group of white-headed langurs adopted behavioral strategies different from those of the bisexual group. This strategy could represent a trade-off between foraging and competition risks and reproductive opportunities for the all-male group.