9.

Abbott's Gray Gibbon

Hylobates abbotti

French: Gibbon d’'Abbott / German: Westlicher Borneo-Gibbon / Spanish: Gibon de Abbott

Other common names: Abbott's Gibbon, West Bornean Gray Gibbon

Taxonomy. Hylobates cinereus abbotti Kloss, 1929,

Indonesia, Pontianak, south-western Borneo.

Until recently, H. abbotti was considered a subspecies of H. muelleri, but morphologically and genetically it is distinct as a species. It hybridizes with H. albibarbis in central Borneo. A population.. in east-central Kalimantan may prove, with further research, to be a morph or a distinct subspecies. There are wide intergrade zones between H. abbotti, H. funereus, and H. muelleri where their ranges meet. Monotypic.

Distribution. SW Borneo (S Sarawak State & West Kalimantan Province), N of the Kapuas River and as far E as the Spaoh (= Saribas), District of Sarawak.

Descriptive notes. There are no specific body measurements available; weight 5.9- 6.4 kg (males) and 5.5-6 kg (females). Abbott’s Gray Gibbon is medium gray; the ventrum and crown are a little darker. Hands and feet are not darkened. The crown hair is directed fanwise from the front of the scalp and is markedly elongated over the ears.

Habitat. Primary and secondary semi-deciduous monsoon, dipterocarp, and tropical evergreen forest. Abbott’s Gray Gibbon is tolerant of selective logging to some extent if sufficient tall, fruit-bearing trees are retained.

Food and Feeding. Its diet undoubtedly includes young leaves,fruits, and flowers and insects, but this species has not been studied in the wild.

Breeding. There is no information available for this species.

Activity patterns. Abbott's Gray Gibbon is diurnal and arboreal.

Movements, Home range and Social organization. There is no specific information available for this species, but it is probably very similar in these aspects to Muller's Gibbon (H. mueller).

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List (as H. mueller: abbotti). Abbott's Gray Gibbon is protected under Indonesian and Malaysian law. As for other gibbons on Borneo, logging, hunting, and deforestation are the main threats. It occurs in five protected areas: Betung-Kerihun and Danau Sentarum national parks in West Kalimantan (Indonesia) and Batang Ai and Bako national parks and Lanjak Entimau Wildlife Sanctuary in Sarawak (Malaysia). The population of Abbott’s Gray Gibbon is not known, but the “gray gibbons” (Miiller’s, East Bornean Gray, H. funereus, and Abbott's Gray gibbons) in Borneo have been estimated at 250,000-375,000 individuals.

Bibliography. Bartlett (2007), Brody & Brody (1974), Chivers (2001), Geissmann & Nijman (2008b), Groves (2001), Haimoff (1985a), Haraway et al. (1988), Kloss (1929), Leighton (1987), Maples et al. (1988), Mather (1992), Meijaard et al. (2005), Mitani (1984, 1985b, 1985c), Nijman (2005b), Short (2004), Stott & Selsor (1961a), Tenaza (1985), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Yasuma & Andau (2000).