Nomascus annamensis, Van et al., 2010

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Hylobatidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 778-791 : 788-789

15.

Northern Yellow-cheeked Crested Gibbon

Nomascus annamensis

French: Gibbon annamite / German: Nordlicher Gelbwangengibbon / Spanish: Gibon de mejillas beige septentrional

Other common names: Annamite Crested Gibbon, Northern Buff-cheeked Crested Gibbon

Taxonomy. Nomascus annamensis Van et al., 2010 ,

Vietnam, Ja Boc, Sa Thay District, Kon Tum Province (c.14° 25’ N, 107° 35’ E, Chu Mom Ray National Park).

This taxon was recently described based on vocal and genetic data that demonstrated it was distinct from N. sik: and N. gabriellae , the latter its closest relative. The species’ distribution covers parts of what was formerly believed to be that of N. gabriellae (to the south) and N. stki (to the north), reducing the distributions of both. Its occurrence in the central Annamite Mountains gives it its specific epithet. Monotypic.

Distribution. S Laos (E of Mekong River, up to approximately the Banhiang River, 16° 00’=16° 03’ N, in Savannakhet Province), C Vietnam (from the Thach Han River, 16° 40’-16° 50” N, in Quang Tri Province in the N to approximately the Ba River, 13° 00’=13° 10’ N, in Gia Lai and Phu Yen provinces in the S), and NE Cambodia (Ratanakiri and Stung Treng provinces, E of the Mekong River and N of the Srepok River, 13° 30’ N).

Descriptive notes. Head-body 46-2 cm (males) and 43-8 cm (females); recorded weight of the adult male type specimen was 7 kg. The Northern Yellow-cheeked Crested Gibbon is largely indistinguishable from the Southern Yellow-cheeked Crested Gibbon (N. gabriellae ). As with other species of Nomascus , it is sexually dichromatic, with males being predominantly black and females being buff-colored. Adult males are black, with a brown tinge on the chest, and have buff cheeks reaching less than halfway up the ears, with a rounded upper margin and brushed out away from the face. Adult females are pale to orange-yellow and have a dark crown-streak of variable size and a variable darker patch on the chest. Infants are born whitish-buff and transition to the same pelage as adult males, which they maintain as juveniles and subadults. Males maintain this pelage throughout adulthood, but females change to their adult buffy pelage at maturity.

Habitat. Broadleaf evergreen and semi-evergreen forest, but probably ranges into more deciduous adjacent habitat types. The Northern Yellow-cheeked Crested Gibbon has been recorded at 50-1205 m above sea level.

Food and Feeding. There is limited field data on diets of Northern Yellow-cheeked Crested Gibbons. Two short studies suggest that it is frugivorous but with significant reliance on leaves, young shoots, and flowers. An instance of predation on a subadult Finlayson’s Squirrel (Callosciurus finlaysonit) by an adult female Northern Yellowcheeked Crested Gibbon and subsequent food sharing have been observed, as have instances of predation on lizards.

Breeding. Two births have been recorded in a wild habituated group in Cambodia. They were in November 2008 and August 2011, suggesting an interbirth interval of about three years.

Activity patterns. The Northern Yellow-cheeked Crested Gibbon is diurnal and arboreal. Activity begins just prior to dawn and often commences with loud vocalizations, usually completed by 07:00 h. One study found activity budgets of 38% feeding, 36% resting, 19% traveling, and 7% other activities. Feeding and travel frequencies are fairly uniform throughout the day, dropping off by 13:00 h for the former and 15:00 h for the latter as individuals settle for the night.

Movements, Home range and Social organization. The Northern Yellow-cheeked Crested Gibbon lives in monogamous family groups consisting of an adult pair and their immature offspring. The home range size of one group was c.50 ha.

Status and Conservation. CITES Appendix I. This newly described species has not been assessed on The IUCN Red List. The presence of the Northern Yellow-cheeked Crested Gibbon has been confirmed in 18 protected areas: Dak Rong, Phong Dien, Ba Na-Nui Chua, Song Thanh, Ngoc Linh, and Kon Cha Rang nature reserves and Bach Ma and Chu Mom Ray national parks in Vietham; Dong Phou Vieng, Xe Sap, Xe Bang Nouan, Phou Xiengthong, Dong Amphan, Dong Houa Sao, and Xe Pian biodiversity conservation areas in Laos; and Virachey National Park in Cambodia. In Vietnam, ¢.200 groups have been recorded between 2000 and 2011, although this represents a minimum number. Key populations are thought to occur in the contiguous Dak Rong and Phong Dien nature reserves, and additional important populations may occur in Kon Cha Rang Nature Reserve and Song Thanh, Ngoc Linh, and Kon Cha Rang nature reserves and surrounding forests. Although data are lacking, populations in Laos are likely significant, but it is inferred that they are declining, with none in effectively managed protected areas. Some locations in Laos, such as Xe Sap National Protected Area, afford good natural protection. Populations in Cambodia are likely to be very important, the most significant being in Virachey National Park with an estimate of over 10,000 individuals, although based on very limited survey data. The adjacent Veun Sai-Siem Pang Conservation Area has a population estimate of ¢.500 groups and is currently under management. The Northern Yellow-cheeked Crested Gibbon is threatened by habitat loss, hunting, and collection for the pet trade. In Cambodia, large areas of habitat in Virachey National Park are being cleared for rubber plantations, and a mining concession over most of the protected area poses threats to this core population. Compared with the more northerly distributed species of Nomascus , however, populations of the Northern Yellow-cheeked Crested Gibbon are relatively robust and intact.

Bibliography. Chivers (2001), Duckworth (2008), Geissmann et al. (2000), Konrad & Geissmann (2006), Lao PDR, MAF (2011), Mootnick & Fan Pengfei (2011), Phan Channa (2008), Rawson et al. (2011), Roos et al. (2007), Schultz (1933), Traeholt, Bonthoeun et al. (2005), Traeholt, Bunthoen et al. (2007), Van Ngoc Thinh, Hallam et al. (2011), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Van Ngoc Thinh, Mootnick, Vu Ngoc Thanh et al. (2010), Van Ngoc Thinh, Rawson et al. (2010).

Figures

12. Western Black Crested Gibbon (Nomascus concolor), 13. Eastern Black Crested Gibbon (Nomascus nasutus), 14. Hainan Crested Gibbon (Nomascus haimmanus), 15. Northern Yellow-cheeked Crested Gibbon (Nomascus annamensis), 16. Northern White-cheeked Crested Gibbon (Nomascus leucogenys), 17. Southern White-cheeked Crested Gibbon (Nomascus siki), 18. Southern Yellow-cheeked Crested Gibbon (Nomascus gabriellae), 19. Siamang (Symphalangus syndactylus)

Distribution. S Laos (E of Mekong River, up to approximately the Banhiang River, 16° 00’=16° 03’ N, in Savannakhet Province), C Vietnam (from the Thach Han River, 16° 40’-16° 50” N, in Quang Tri Province in the N to approximately the Ba River, 13° 00’=13° 10’ N, in Gia Lai and Phu Yen provinces in the S), and NE Cambodia (Ratanakiri and Stung Treng provinces, E of the Mekong River and N of the Srepok River, 13° 30’ N).