It might be argued that the behavioral and ecological diversity exhibited by the Hylobatidae is less than that exhibited by other primate families. For the most part all gibbon species share similarities of diet, range use, and social structure. In contrast, great apes, which most taxonomists place in a single taxonomic family, often with humans as well (i.e., Hominidae), differ markedly along these same axes. An explanation for the relative homogeneity in gibbon behavioral ecology can perhaps be found in the “radically new feeding niche” gibbons evolved to exploit. According to Ellefson (1974) the elements of the adaptive complex that define the gibbon pattern-terminal branch feeding (with brachiation), territoriality, and pair living-are mutually interdependent and, therefore, highly resistant to change. Whether or not this scenario is accurate, the existing field data do suggest that gibbon species (at least at the generic level) share many aspects of their behavior and feeding ecology (Chivers 2001; Bartlett 2007a). For this reason I will begin this chapter with an overview of hylobatid evolution and taxonomy. Once I have situated white-handed gibbons within their broader taxonomic unit, I turn to a description of the study area where I worked, including the trail system, fauna, and forest

phenology. I close the chapter with a description of the study animals and an overview of behavioral observation methods used during my research.