Conservation Status of the Northern Yellow-Cheeked Crested Gibbon (Nomascus annamensis) in Vietnam

We review the results of recent surveys for the northern yellow-cheeked crested gibbon (Nomascus annamensis) on the eastern slope of the Annamite Range in Binh Dinh and Quang Ngai provinces, and update its conservation status in Vietnam. Surveys were conducted in three adjacent forest blocks: West Ba To Proposed Nature Reserve (NR), An Toan NR and Vinh Son Commune, with a total area of 367 km2. We documented gibbon densities of 0.41 and 0.15 groups/km2 in the first two sites but did not find any groups in the third location. We detected 46 groups and estimated 114 groups in these areas, about 14 per cent of Vietnam’s known population of N. annamensis. Our archival study revealed that at least 317 groups of this species have been confirmed in Vietnam. The distribution range is between approximately 14° 00′ and 16° 50′ N latitude with potential overlap with the southern white-cheeked gibbon in the northernmost portion of this range. Important drivers influencing the distribution of the species in Vietnam include temperature seasonality, elevation, precipitation of the driest month, annual precipitation, and precipitation of driest quarter. This species faces extinction in Vietnam due to fragmented habitat, small subpopulation sizes, illegal hunting and forest conversion.