THE YELLOW-CHEEKED GIBBON (HYLOBATES-GABRIELLAE) IN NAM-BAI-CAT-TIEN (SOUTHERN VIETNAM) REVISITED

Data concerning the status, habitat, and vocalizations of yellow-cheek ed crested gibbons (Hylobates gabriellae) were collected during a shor t field trip to the Nam Bai Cat Tien National Park (southern Vietnam). Nam Bai Cat Tien may be the southernmost locality where crested gibbo ns (i.e. the Hylobates concolor group) still survive. Fewer songs were heard at Nam Bai Cat Tien National Park than at other crested gibbon sites visited by the author. At least two gibbon groups appear to have been greatly reduced in number since previous surveys in the park. Th ere is some evidence that both the gibbon population and the gibbon ha bitat in Nam Bai Cat Tien are disturbed. The first case of a great cal l solo song in wild gibbons of the concolor group is reported. Great c alls of H. gabriellae are described and documented with sonagrams for the first time. They differ from those previously described for H. leu cogenys.