No abstract

We describe and illustrate with sonograms the loud calls of a monogamous, territorial ape, the lar gibbon (Hylobates lar). We attempt an overview of its repertoire of loud calls, their organisation, contexts and functions. The description is based on a two year study of a wild population in Khao Yai National Park, Thailand. We distinguish seven classes of call bout: male solo, male dispute calls, female solo, normal duet by bonded pair, ooaa duet (similar to normal duet, but more infectious to other groups), disturbed calls and contact calls. The organisation of the normal duet is described in detail, showing the coordination of the sexes, the development of the male part through the call bout, and the presence of individual and pair differences. The discussion considers the possible functions of duets, of male solos, and of disturbed calls given in reaction to man.

No abstract

The monthly medians of the distances traveled daily by siamang and lar gibbons are negatively correlated with rainfall and positively correlated with the separate and combined abundance of different food categories. The latter correlations indicate that the apes follow a policy of cutting their losses by reducing travel when food abundance falls.

No abstract