A brief survey for crested gibbons in Bach Ma National Park, central Vietnam

We carried out a short survey for gibbons in the Bach Ma National Park (Thua Thien Hue Province) of central Vietnam. During eight survey days, eight different groups (including solitary males) were heard. All gibbons appeared to live in lowland evergreen forest at altitudes between 400 and 800 m, although the park area also includes forest areas at higher altitudes. Most gibbon songs (53%) started at dawn, between 05:00 and 06:00 hours. Our preliminary density estimate of about 1.3 goups/km 2 compares well with estimates of southern Nomascus populations and appears to be higher than at least some estimates from northern populations. We also carried out tape-recordings of the gibbons’ songs. A comparative analysis of these recordings will be helpful in resolving the uncertainties about the taxonomic status of gibbons in central Vietnam and adjacent parts of Cambodia and Laos.