Bioacoustics of Hylobates klossii

Activity patterns. Kloss’s Gibbons are diurnal and arboreal. Groups spend much of their day at rest. They do not use the same sleeping tree two nights in a row and choose sleeping sites that do not have biting ants. They also prefer sleeping trees that lack hanging lianas, which may be an adaptation to avoid human predation because Mentawai hunters often climb lianas to shoot primates. Unlike most other gibbons, Kloss’s Gibbons do not sing duets. Instead, adult males sing from sleeping trees in the hours before dawn, sometimesas early as 01:00 h. Adult females typically chorus after the first feeding bout of the day (07:00-09:00 h). Singing appears to be contagious, and male bouts typically occur in “countersinging” interactions, in which adjacent individuals take turns singing and avoid overlapping. Neighboring females may produce songs in synchrony. The greatcall of the female Kloss’s Gibbon has been described as “the finest music uttered by any land mammal,” and itis often accompanied by an acrobatic display. Females exhibit structural individuality in their songs, such that each female can be distinguished by their song alone. The male’s song is simpler than the female’s. As in other gibbons, the primary function of the female's song is to defend the territory and possibly to advertise mated status. Solitary, “floating” male Kloss’s Gibbons that do not occupy a territory have been observed to sing, suggesting that mate attraction may be a function of the male’s song.