White-Handed (Lar) Gibbon
Body length is 44-63 cm (just under three feet). Average weight is 5.5 kg (14 pounds). Males and females are similar. Color is variable. In Thailand there are two colors, not related to sex- very dark brown (black) or light buff. They all have a pronounced and complete white face ring, white hands and feet. Male song is simple with quaver-hoots, female song is longer, rising to climax, about 18 seconds long. (Populations from N. Sumatra: brown/red/buff, song 17 seconds long.) Fur is extremely dense, providing protection from rain. One square centimeter of skin has over 2,000 individual hairs (13,125 per sq. in.) compared to 900 hairs per sq. cm. for Old World monkeys. Arms are very long , fingers are long and hook-like, and thumbs are thin and somewhat reduced. No tail. Ischial callosities are present.
GEOGRAPHICAL RANGE AND HABITAT:
Middle and upper stories of deciduous monsoon and evergreen rain forest in southern Burma, Thailand, the Malay Peninsula, Sundaland to North Sumatra. (Also Indochina & Tenasserim) Recently extirpated in Lancang county, China.
Fruit specialists (diet 75% ripe fruit) - figs a favorite. May visit 16 or more widely spaced food trees in a day's foraging. Rest of diet consists of leaves, young plant shoots, flowers, birds' eggs, birds, insects, and spiders. Zoo diet is primate chow, fruits, vegetables and browse. They drink by licking their own fur after a storm, or dipping an arm into a tree hole or rubbing it on wet foliage.
LIFE CYCLE/SOCIAL STRUCTURE:
Gibbons are the only pair-bonded higher primate (with arguable exception of humans; only 3% of mammals and 14% of primates are monogamous). Gibbons live in small family groups consisting of the mated pair and their immature offspring. There is almost no sexual dimorphism and males are not socially or physically dominant over females. They are vigorously territorial, spending up to 1/2 hour or more each morning calling and displaying. The function of calling seems to be both territorial and to reinforce the pair bond. The calling bout is usually initiated by the female. Male and female "duet" with different "songs." The female song is a plaintive swooping call, rising to a crescendo - her great call; the male calls with a high-pitched "quaver song." The male usually takes the lead in attacking other gibbons encountered, although actual fighting is uncommon. There is no particular breeding season. Estrous cycle is 30 days. Young are born singly at intervals of two to four years after a gestation period of about 210 days. Infants are hairless except for a cap of fur on the crown and must be sheltered between mother's thighs and abdomen to keep warm. Young leave the group at sexual maturity, between ages of six and eight years, driven out by the same-sex parent. Life span is 30 to 40 years.
These are the most active of all gibbons. They move faster, more quietly, and farther each day than any other forest apes or monkeys. Brachiation comprises 90% of locomotor activity. Can easily leap a gap of 30 feet between one tree and another, (but because they can not swim, they avoid crossing open water). Adaptations include precision of movement, incredible eye-hand coordination and dexterity. This remarkable agility makes a healthy adult gibbon virtually invulnerable to predation. They sleep sitting on their ischial callosities, hands resting upon flexed knees and head buried between knees and chest.
Unlike the great apes, the gibbons are a diversified array of species showing variations on the adaptive theme of a rapid hand-over-hand locomotion perfected for feeding on buds, leaves, and fruits out at the ends of branches. There are 9 species with 9 different territorial songs. All are monogamous. The songs are inflexible and seem to be innate, not learned. There are three subspecies of lar gibbon. Ours are probably H.l. entelloides from Thailand, based on their song characteristics. Hylobates means "dweller in the trees." Evidence from healed bone fractures show that gibbons do sometimes fall.
1 Male. 1 Female The male (born in 1983) came here from the San Ana Zoo in 1986. The female (born in 1981) came here from the Dickerson Park Zoo in 1984.
STATUS IN WILD:
Gibbons are absolutely dependent upon old growth tropical forests. Lar gibbons retain only 10% of their original habitat in protected reserves. In 1987, the IUCN estimated that there were 79,000 lar gibbons but to protect the more endangered species, all are listed as endangered by the USDI (1980) and are on appendix 1 of the CITES, prohibiting commercial trade in gibbons.