The organization of song in the Hainan black gibbon (Hylobates concolor hainanus)

There have never been any documented studies on the vocal or non-vocal behaviour of wild or captive Hainan black gibbons, which are highly endangered in the wild (Hainan Island, China), and very scarce in captivity. The singing behaviour of the only pair of captive Hainan black gibbons outside Southeast Asia was observed, recorded and analyzed in detail. This adult pair produced duets only, with the organizational features of their duets found here to be similar to that in two other concolor gibbon sub-species; however, the acoustical features were very different from any other concolor gibbon pair studied previously. Some functional and evolutionary implications of the singing behaviour of the Hainan black gibbon are presented and discussed.