Long-term home range use in white-handed gibbons (Hylobates lar) in Khao Yai National Park, Thailand.

ABSTRACT

Ranging behavior is an important element of how nonhuman primates obtain sufficient resources to ensure biological maintenance and reproductive success. As most primates live in permanent social groups, group members must balance the benefits of group living with the costs of intragroup competition for resources. One way to mitigate the cost of intragroup feeding competition is to increase foraging-related travel, thereby increasing the number of patches visited. As a result we might expect home range size to increase as a function of group size. On the other hand, for perennially territorial species, ranging behavior may be constrained by the ranging requirements of territorial defense or by the location of neighboring territories, which would result in long-term stability in the size and location of a group's home range. In this study, we examined changes in range-use characteristics in one well-habituated group of white-handed gibbons (Hylobates lar) during three study periods over a 10-year span. Group size changed from five members, two adults, two juveniles, and one infant, in 1994, to two adults in 2002, and to three adults and one sub-adult in 2004. Despite inter-annual changes in core area use we found that home range location was highly stable across years. Nevertheless, home range size was larger and daily path length significantly longer in 2002 relative to 1994 when a dependent infant was present in the group. The percentage of time adults spent resting was also significantly greater in 1994 when the infant was present. These findings highlight the importance of considering group composition, in addition to group size, when evaluating the determinants of ranging behavior. We also consider the influence of individual and shared knowledge on home range stability.