Habitat Type and Group Identity Influence Activity Budgets in White-Handed Gibbons (Hylobates lar) in Two Habitat...

Activity patterns reveal important information about how primates cope with challenging ecological conditions. This study investigates behavioral variation in white-handed gibbons (Hylobates lar) living at the ecological extreme of their range in a heterogeneous landscape in western Thailand. We spent 13 months studying 4 groups at Khao Nang Rum Wildlife Research Station in Huai Kha Khaeng Wildlife Sanctuary, where gibbons are found living in both evergreen and savannah habitats, both of which we describe as poor-quality habitat. Given specific phenological properties (e.g., predominance of deciduous species) of the savannah habitat, we predicted that food resources would be less available in the savannah habitat compared to the evergreen habitat, making the savannah an even lower quality habitat for these frugivorous apes. The evergreen habitat produced more fruit and young leaves throughout all three seasons, and more flowers during the wet season, compared to the lower-quality savannah habitat. We furthermore predicted that habitat type would drive differences in activity budget. Gibbons in both habitats exhibited high rates of resting behavior (50.1% evergreen, 52.3% savannah), possibly in response to a particularly dry year. However, while activity budget differed between habitats, group identity was a better predictor of this variation. Specifically, compared to evergreen gibbons, savannah gibbons spent more time feeding (28.9% vs. 22.5%) and less time vocalizing (4.2% vs. 12.1%), but this varied between the two savannah groups with one group spending more time traveling (7.7% vs. 3.6%) and less time resting (50.0% vs. 58.4%) than the other group. We suggest that gibbons at this poor-quality site, and specifically in the even lower quality savannah habitat, are responding to the availability of specific key resources within their home ranges and that groups in the savannah habitat are employing unique strategies in response to the relative scarcity of fruit resources compared to the evergreen habitat.