Gibbon , common name for any of the small anthropoid apes found in the subequatorial forests of India, Indochina, and the Malay Archipelago. The gibbon is a slender animal with a small, round head and soft, woolly fur. Its most notable characteristic is its long arms, by which it swings from tree to tree with great agility, using its hands as hooks rather than grasping the limbs. A large gibbon stands 75 to 90 cm (30 to 35 in) high; the arm span is nearly twice as long. The gibbon is the only anthropoid ape to walk on its hind limbs only, usually raising its arms for balance. Gibbons are monogamous; the young, born singly, remain with the family group until they are five or six years old. The animals eat leaves, fruit, flower parts, insects, spiders, birds, and birds' eggs. They are usually quiet during the day but commonly howl at sunrise and in late afternoon. About nine species of gibbons exist. The silvery gibbon, or wou-wou, of Java is ashy gray; the whitehanded gibbon, or lar, of the Malay Peninsula is distinguished by its white hands and feet and its musical howl. The largest gibbon is the siamang of Malaysia and Sumatra. In 1979 the Grant Park Zoo in Atlanta, Georgia, reported a four-year-old female "siabon," the hybrid offspring of a male silvery gibbon and a female siamang; this was the first known mating involving different primate species. Populations of wild gibbons have been severely reduced due to hunting and deforestation .