Hylobatid Diets Revisited: The Importance of Body Mass, Fruit Availability, and Interspecific Competition

In general, hylobatids are ripe-fruit specialists (MacKinnon and MacKinnon 1980; Chivers 2001) that use figs as fallback resources (Marshall 2004; Marshall et al. this volume). Despite the widespread assumption that siamangs (Symphalangus syndactylus) are true folivores, the idea that siamangs are dependent on figs to the same degree as other hylobatids is not new. Chivers and Raemaekers (1986) proposed that siamangs are more accurately described as “fig seekers,” an idea supported by Palombit’s (1997) research. Chivers and Raemaekers (1986) labeled small-bodied gibbons, by contrast, as fruit-pulp specialists. However, both Palombit (1997) and Marshall (2004) found that small-bodied gibbons (H. lar and H. albibarbis respectively) emphasized fig eating to the same extent as siamangs. Both siamangs and white-handed gibbons have been observed to preferentially feed on figs, even when other, more sugary fruits were available (Palombit 1997). Although nutritionally inferior to sugary fruits, figs occur in large patches, have high species diversity at individual sites and fruit asynchronously both within and between species (Raemaekers 1978b; Raemaekers et al. 1980). Thus, for gibbons, figs have the potential to provide a stable food source to meet their basic energetic requirements.