Animals

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.