Can a group elicit duets from its neighbours? A field study on the black-crested gibbon (Nomascus concolor jingdongensis) in Central Yunnan, China.

We tested the intergroup spacing hypothesis with a 13-month field study of the interaction of singing behaviour between 3 neighbouring groups of black-crested gibbons (Nomascus concolor jingdongensis) at Mt. Wuliang, Central Yunnan, China. Neighbouring groups tended not to sing on the same day. While it did happen occasionally, a group seldom started a duet while its neighbour was singing, or within 5 min of the singing ceasing. The intersong intervals of 2 groups calling on the same day were similar or significantly longer than the intervals between any song bouts randomly selected from the same 2 groups when calling on different days. Groups did not sing in intergroup encounters and showed similar responses to neighbouring groups and groups with no common border. These results did not support the intergroup spacing hypothesis. The possible reasons are discussed.