Hylobates pileatus Gray 1861

11.

Pileated Gibbon

Hylobates pileatus

French: Gibbon a bonnet / German: Kappengibbon / Spanish: Gibon crestado

Other common names: Capped Gibbon, Crowned Gibbon

Taxonomy. Hylobates pileatus Gray, 1861,

Cambodia.

Based on reports beginning in 1925, the Pileated Gibbon forms a narrow hybrid zone with H. lar in Khao Yai National Park, central Thailand, specifically, in the headwaters of the Takhong-Mun-Mekong river system. Monotypic.

Distribution. SE Thailand (E & S of the Mun and Takhong rivers, W limit may have formerly been the Bang Pakong River), SW Laos (W of the Mekong River), and N & W Cambodia (W of the Mekong River); the species may have formerly occurred in S Vietnam.

Descriptive notes. No specific measurements are available. Male and female Pileated Gibbons are very different in their pelage color. Adult males are almost completely black except for a whitish border surrounding their face (sometimes just a brow band or a pair of long grayish fringes along each temple). Males have white hands and feet (some earlier researchers mistakenly classify them as a separate form) and a white pubic tuft. Females and juveniles are silvery-gray or fawn-buff with black on the crown cap, cheeks, and chest (spreading down the inner surfaces of limbs with age), and a white face-ring. The crown hair is directed fanwise from the front of the scalp.

Habitat. Moist, seasonal evergreen and mixed deciduous-evergreen forests up to elevations of 1200 m in Thailand and up to 1500 m in Cambodia. They prefer mid- and high canopies.

Food and Feeding. The Pileated Gibbon is similar to the Lar Gibbon (H. lar) in diet and general ecology, consuming mostly fruits (71%), flowers (15%), young shoots (2%), and some immature leaves and insects.

Breeding. Infant Pileated Gibbons are cream-colored until about the end of their first year when the coat becomes silvery-buff until puberty. At this point, malesstart to take on their very different adult coloration. Full maturity occurs at 6-8 years in both males and females. Individuals may live up to 39 years.

Activity patterns. The Pileated Gibbons is diurnal and arboreal. Groups spend much of their day at rest. They sleep an average of almost 16 hours/day, rising at dawn and concluding their activities until about mid-afternoon (12:45-15:50 h). The Pileated Gibbon is somewhat shyer and more elusive than the Lar Gibbon.

Movements, Home range and Social organization. Pileated Gibbons are largely monogamous, but polygynous pairings have been reported in the hybrid zone at Khao Yai National Park, Thailand. Home ranges are 15-50 ha. Males are mainly responsible for defending the group’s territory and leading its daily progressions. Mixed groups of the Lar and Pileated gibbons with two adult females have been reported in Thailand. The average group size in Thailand is four individuals. Densities are generally low in Thailand, averaging close to 1 group/km? or 4 ind/km?, with pockets of higher density in some remote mountain areas. In the Cardamom Mountains of Cambodia, densities are 1-2 groups/km?®. No density figures are available for Laos.

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List. The Pileated Gibbon is threatened by continued loss of habitat due to fragmentation and degradation, with many populations isolated in small pockets of montane forest. It is occasionally hunted for food. Many populations in Cambodia do not occur in protected areas and suffer from habitat loss due to logging, agriculture, hydroelectric development, and new human settlements. These are major threats, especially in remote areas. In Thailand, all remaining populations are now in protected areas, but subsistence hunting by minor forest-product collectors is still uncontrolled. The Pileated Gibbon occurs in 25 protected areas: Beng Per Wildlife Sanctuary, Preah Monivong (= Bokor), Botum Sakor, and Kirirom national parks, Preah Vihear and Central Cardamom Mountains protection forests, and Kulen Promtep, Phnom Aural, and Phnom Samkos wildlife sanctuaries in Cambodia and Phu Chong-Na Yoi, Namtok Phliu, Khao Chamo-Khao Wong, Khao Khitchakut, Khao Yai, Pang Sida, Thab Lan, and Ta Phraya national parks and Khao Ang Rue Nai, Dong Yai, Huai Sala, Phanom Dong Rak, Yot Dom, Khlong Khrua Wai, and Khao Soi Dao wildlife sanctuaries in Thailand. In 2005, it was estimated that there were more than 35,000 individuals in Cambodia and 13,000-14,000 in Thailand. In Cambodia, the most important area for Pileated Gibbons is the Cardamom Mountains, with an estimated 20,000. In Thailand, an estimated 12,000 survive in four principal protected areas (Khao Yai, Thab Lan, Khao Ang Rue Nai, Khao Soi Dao), while another 1000-2000 occur in 15 other highly fragmented protected areas. Numbers for Laos are unknown, but they are believed to be significantly lower due to their limited range in the country.

Bibliography. Badham (1967b), Braendle & Geissmann (1997), Brandon-Jones (1995c), Brockelman (1983), Brockelman, Damman et al. (1977), Brockelman, Geissmann et al. (2008), Chivers (2001), Duckworth (2008), Geissmann (1983, 1984, 1991a, 1991b), Geissmann & Braendle (1997), Groves (2001), Leighton (1987), Marshall & Brockelman (1986), Montagu (1950), Mootnick (1997), Phoonjampa & Brockelman (2008), Srikosamatara (1980, 1984), Srikosamatara & Brockelman (1987), Traeholt et al. (2005).