Life at the extreme: the behavioral ecology of white-handed gibbons (Hylobates lar) living in a dry forest in Huai Kha Khaeng Wildlife Sanctuary, Western Thailand

Gibbons are most commonly characterized as being ecologically restricted due to a suite of morphological traits that evolved to exploit a ripe fruit niche. However, there is considerable between-species variation in dietary and social behaviors, providing an interesting taxon with which to examine behavioral flexibility. Yet because most species have only been studied in one habitat type, it has been difficult to determine whether these differences are the result of unique evolutionary histories or proximate responses to local ecological conditions. My research explores the extent and limitations of behavioral flexibility in Endangered white-handed gibbons (Hylobates lar) living in two distinct habitats at the ecological extreme of their range. I collected thirteen months of behavioral, spatial, and dietary data from four gibbon social groups in two distinct habitats living in Huai Kha Khaeng Wildlife Sanctuary. I used satellite images to differentiate habitat types. I also monitored 17 kilometers of botanical transects and identified differences in fig availability, canopy cover, and forest productivity between habitats. In response to these differences, gibbons altered ranging behaviors, activity budgets, and diets. Compared to gibbons in evergreen habitat, gibbons in mosaic habitat required home ranges twice as large; ranged in different parts of the range each month; spent more time feeding and less time vocalizing; ate a diet higher in non-fig fruit and vine shoots and lower in fig fruit; and reduced foraging efforts when flowers were abundant. My results demonstrate that gibbons can significantly adjust fundamental behaviors in response to challenging local ecological conditions.