ABSTRACT
The nine species of gibbons (genus Hylobates) are the fourth-nearest living relatives of human kind. They are arboreal apes, inhabiting the cli max forests of Southeast Asia. All species are monogamous and strongly territorial (Marshall Sc Sugardjito, 1986; Prueschoft, Chivers, Brockelman, Sc Creel, 1984). All may be identi fied by their territorial songs, which are unique to each species (Marshall Sc Marshall, 1976).
