Family formation strategies of Kloss's gibbons.

This study describes how adults of Kloss's gibbons (Hylobates klossii) inhabiting the central rain forest of Siberut Island, Indonesia, help their offspring achieve reproductive success. Adults of these monogamous apes exclude maturing offspring from the family and territory through intrasexual aggression. Adults may then assist the offspring to establish a territory contiguous to theirs. Aid may take the form of accompanying offspring into suitable areas not yet occupied or forcefully annexing part of an adjacent territory. Replacement of an adult by its offspring may also occur. A conclusion is that the probability of a young gibbon gaining a territory and mate is greater in the proximity of its parental group than in areas farther afield.