Cao Vit Gibbons ( Nomascus nasutus ) Sing at Higher Elevation but Not in Peripheral Areas of Their Home Range in a Karst Forest

Gibbons’ loud morning songs are hypothesized to function in territorial defense. To efficiently defend their territory, gibbons could sing more frequently along the territory boundary. Alternatively, singing may advertise occupancy of a territory, regardless of the singer’s location. Further, gibbons should choose singing sites that facilitate sound transmission. We investigated singing site choice of two groups of cao vit gibbon ( Nomascus nasutus ) from 2008-2009 and 2012-2013, in Bangliang Gibbon Nature Reserve, Guangxi, China. We did not find that groups sang more frequently than expected at the periphery of their home ranges, which does not support the boundary defense hypothesis. Instead, groups sang from the core area or irrespective of locations within an established territory, supporting the hypothesis that they advertise continuous occupancy of territories through regular singing. Singing locations were at significantly higher elevation than non-singing locations for both groups in the two study periods, supporting the hypothesis that cao vit gibbons choose singing locations to maximize sound transmission and minimize signal attenuation in karst forest. Thus, although the sample size is small, our study suggests that gibbons display flexibility in their choice of singing sites in different environments to ensure they can defend their territory.