The Conservation Status of Gibbons in Vietnam - Gibbon Research ...

The Conservation Status of Gibbons in Vietnam10 Ecology and Behaviour of Crested Gibbons10.1 IntroductionAt the turn of the 21st century, the Nomascus genus was probably the least studied genera of theHylobatidae. Very few of the seven species in the genus had been studied at that time, and mostwork had been conducted in China on N. concolor and over short periods of time. In the decadesince the publication of the first Vietnam gibbon status review (Geissmann et al. 2000), however,considerable additional research has been conducted on members of the Nomascus genus.Longitudinal studies have now been completed on several taxa, and work is ongoing on others.Despite the only recent rediscovery of N. nasutus in 2002 (La Quang Trung & Trinh Dinh Hoang2004) there is a growing body of work on this taxon’s ecology, including social structure (FanPengfei et al. 2010), diet (Nguyen Thi Hien 2007; Fan Pengfei et al. 2011) and ranging behaviour(Fan Pengfei et al. 2010), and it stands to become one of the best described species in the genus.Nomascus concolor remains a focus of research, with a steady stream of published results comingout of China since the 1990s, including recent work on group structure (Fan Pengfei et al. 2006;Fan Pengfei & Jiang Xuelong 2010), diet (Fan Pengfei & Jiang Xuelong 2009; Fan Pengfei et al.2009), ranging behaviour (Fan Pengfei & Jiang Xuelong 2008a), activity budgets (Fan Pengfei et al.2008) and other aspects of the species ecology (Fan Pengfei et al. 2007; Fan Pengfei & JiangXuelong 2008b).Nomascus leucogenys represents an ongoing research gap, with only a single study, which wascompleted in the 1980s (Hu et al. 1989). Published ecological work is still missing for N. siki. Somepreliminary results on diet exist for N. annamensis (Traeholt et al. 2007; Phan Channa 2008);however, a habituated group of the species in Cambodia is the subject of ongoing research andpromises to return additional information over coming years. N. gabriellae is the best studiedspecies of the light-cheeked gibbons and has been the subject of one long-term study (Kenyon2007) which has revealed significant detail about its ranging behaviour, group structure and diet.While there are still many gaps in our knowledge, a picture of the Nomascus genus is slowlyemerging, and there are some tantalizing suggestions that it differs in some ways from othergibbon genera. This chapter aims to summarise ecological information on each species of gibbonfound in Vietnam.10.2 Ecology of Crested Gibbons in ContextGibbons have generally been characterized as monogamous in the literature since the first studiesof Carpenter (1940), with families consisting of an adult male, adult female and up to threeoffspring (Bartlett 2007). As additional field data has been collected, however, it is becomingapparent that while it may be that paired monogamous groups are the norm, gibbons showsignificant variation in this respect. Extra-pair copulations and mate replacement have been notedin some species (Palombit 1994; Reichard 1995; Kenyon 2007) and instances of more than twoadults in a single group make up 10% or more of all observation across the Family Hylobatidae(Fuentes 2000). Nomascus gibbons have been particularly important in redefining, or at leastquestioning, the previous paradigm with suggestions of social polygamy in N. concolor (Haimoffet al. 1986; Fan Pengfei et al. 2006; Fan Pengfei & Jiang Xuelong 2010), N. nasutus (Fan Pengfei etal. 2010) and N. hainanus (Liu Zhenhe et al. 1989; Jiang Zhou et al. 2005). Variability within thegenus needs further assessment to determine the extent and frequency of this pattern.Data on maturity in Nomascus gibbons is lacking, however in general gibbons may reach maturityas early as five years of age in captivity, although average age, especially in wild conditions, islikely to be closer to 7-8 years (Geissmann 1991), with both sexes subsequently dispersing fromtheir parents’ territory (Leighton 1987; Bartlett 2007). Studies of Hylobates lar provide the only111