Trachypithecus crepusculus (Elliot, 1909)

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Cercopithecidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 550-755 : 748

152.

Indochinese Gray Langur

Trachypithecus crepusculus

French: Langur gris / German: Indochina-Brillenlangur / Spanish: Langur gris de Indochina

Taxonomy. Presbytis crepuscula Elliot, 1909 ,

Burma, Mount Muleiyit, 1500 m.

There is some geographic variation. Individuals from the north-eastern part of its distribution tend to be darker, particularly on the limbs and tail. Genetically, no large differences are found throughout its distribution. 7. crepusculus is an ancestral hybrid between the francoisi and obscurus species groups. 1. crepusculus is a member of the obscurus species group, which also includes 1. obscurus , I. barbei , and 1. phayrei . Monotypic.

Distribution. SW China (E of Salween River and S of Xishuanbanna, S Yunnan Province), S Myanmar, N Thailand (S to Raheng, and W to the coast of the Bay of Bengal), N & C Laos, and N Vietnam, the W limit is most likely the Salween River; S of the distribution of Phayre’s Langur (1. phayrer).

Descriptive notes. Head-body c.51 cm (males) and c.49 cm (females), tail ¢.83 cm (males) and c.82 cm (females); weight ¢.6-9 kg (males) and c.6-4 kg (females). Female Indochinese Gray Langurs are slightly smaller than males. Body and tail are light gray, and belly is slightly brighter and silvery gray. Forehead, cheeks, and hair around face is brown. Feet and hands are dark gray. Color of forearms merges into light gray color of body. Tail ends with a thin tassel. Head has no crest but long hairs form a whorl. Bare facial skin is dark gray, with full light eye rings and depigmented patches in the middle of upper and lower lips.

Habitat. Primary and secondary evergreen and semi-evergreen forests, mixed moist deciduous forests, and also light woodland, bamboo-dominated areas, near plantations, and even in limestone regions. In Laos, it occurs in limestone (karst) forests. Depending on the region, the Indochinese Gray Langur is sympatric with members of the francoisi species group and the Red-shanked Douc ( Pygathrix nemaeus ).

Food and Feeding. The Indochinese Gray Langur is largely folivorous and also eats figs, bamboo shoots, seeds, flowers, and gums.

Breeding. Ovarian cycle of the Indochinese Gray Langur is ¢.28-4 days, and females undergo an average of 3-6 cycles until conception. The average gestation period recorded for seven females was c.205 days. Births occur throughout the year, but most are in November—April. Interbirth intervalsif the previous infant survives are c.2 years.

Activity patterns. There is no information available for this species.

Movements, Home range and Social organization. Groups of Indochinese Gray Langurs can be as large as 14-20 individuals, with 1-5 adult males and 2-12 adult females. Home ranges are 73-7-93-4 ha. Females disperse and regularly transfer among groups. After immigrating, they can quickly take over the alpha position in the female hierarchy. Population densities recorded for Nam Nao National Park and Phukhio Wildlife Sanctuary in Thailand were 23-38 ind/km?, or an average of 3-4 groups/km?.

Status and Conservation. CITES Appendix II. Classified as Endangered on The [UCN Red List (as 1. phayrei crepuscula ). Although the Indochinese Gray Langur has a wide distribution, it is rarely seen, and populations can be expected to have declined severely in recent years. It is threatened by habitat loss and hunting throughout its range. It often develops large gallstones that are used in traditional Asian medicine. A global population estimate is not available. In China, Indochinese Gray Langurs have been extirpated from many areas and have fallen to less than 5400 individuals (this number includes also the “Shan States Langur,” 1. phayrei shanicus). Due to low densities and its presence in few isolated localities, the Indochinese Gray Langur is considered critically endangered in Vietnam. In Laos, it is rare with only a few records. The Indochinese Gray Langur occurs in Pu Mat, Ben En, Xuan Lien, and Pu Luong national parks and Muong Ne Nature Reserve in Vietnam; Phou Dendin, Nam Et-Phou Louey, Phou Khaokhoay, and Nam Kading national biodiversity conservation areas and Phou Gnouey Production Forest in Laos; Nam Nao National Park and Huai Kha Khaeng and Phu Khieo wildlife sanctuaries in Thailand; and Ailaoshan, Huanlianshan, Wuliangshan, Xishuangbanna, Fenshuiling, Niuluohe, Caiyanghe, and Lancangjiang national nature reserves in China.

Bibliography. Bleisch, Brockelman et al. (2008), Borries, Larney, Derby & Koenig (2004), Borries, Larney, Kreetiyutanont & Koenig (2002), Geissmann et al. (2004), Groves (2001), Liedigk et al. (2009), Lu et al. (2010), Nadler et al. (2003), Pages et al. (2005), Roos et al. (2007), Timmins, Duckworth et al. (2013), Zhang Yongzu et al. (2002).

Figures

149. Tenasserim Langur (Trachypithecus barber), 150. Dusky Langur (Trachypithecus obscurus), 151. Phayre’s Langur (Trachypithecus phayrei), 152. Indochinese Gray Langur (Trachypithecus crepusculus), 153. Cat Ba Langur (Trachypithecus poliocephalus), 154. White-headed Langur (Trachypithecus leucocephalus), 155. Delacour’s Langur (Trachypithecus delacouri), 156. Francois’s Langur (Trachypithecus francoisi), 157. Black Langur (Trachypithecus ebenus), 158. Laos Langur (Trachypithecus laotum), 159. Hatunh Langur (Trachypithecus hatinhensis)

Distribution. SW China (E of Salween River and S of Xishuanbanna, S Yunnan Province), S Myanmar, N Thailand (S to Raheng, and W to the coast of the Bay of Bengal), N & C Laos, and N Vietnam, the W limit is most likely the Salween River; S of the distribution of Phayre’s Langur (1. phayrer).