Responses to Inter-group Encounters of the Hainan Gibbon Nomascus hainanus

The Hainan gibbon (Nomascus hainanus) is one of the most endangered primates and the least studied gibbon species in the fieldwork. In the past decades only a little information was known about its population size, population structure, habitat and food kinds. Through four years field work, we observed their inter-group encounters for four times. We found that their encounter behaviors were much different from other gibbon species. Only vocal and chasing behavior happened between the adult females, male sub-adults and male juveniles of the Hainan gibbon encounters. The time of inter-group encounters was much shorter than other gibbon species, just 24-51 minutes. Not like the Hylobates lar encounters, no fighting was observed among the Hainan gibbon encounters; there was also no such behaviors as playing and grooming, even the extra-group-copulations. The adult females of two groups didn’t take par in the chasing and they only rested and watched 20-30m away. We speculated that the behavior of the adult females may be interpreted as protecting their territory and by the way of chasing the sub-adults can learn how to protect their territory in the future.