A review of the distribution of a new gibbon species: the northern yellow-cheeked crested gibbon nomascus annamensis Thinh, Mootnick, Thanh, Nadler and Roos, 2010

Nomascus annamensis is a newly described gibbon endemic to the Indochina peninsula (Cambodia, Laos and Vietnam). We review the published and unpublished literature relevant to N. annamensis to clarify its distribution and help inform conservation management and policy related to this species. The best current distribution estimate for N. annamensis is east of the Mekong River, from 16°55'N to approximately 14°00'N in central Vietnam, and from 16°00'N in the south of Laos to about 13°57'N in northeast Cambodia. There is a large forest tract overlapping the borders of Cambodia, Laos and Vietnam that is probably an important habitat for this gibbon. The distribution and population status of this species in Cambodia and Laos is poorly known, however. In addition, information on the biogeographic boundaries with other gibbon species is still lacking. Various biogeographic barriers based on rivers and forest types have been hypothesized to explain the biogeography of gibbons in this region; however, our review of the evidence suggests that these factors might not fully explain the distribution of Nomascus annamensis and its close relatives (N. siki and N. gabriellae). We propose that climatic conditions may be a driver shaping the distribution of the gibbon. Further studies are needed, therefore, to provide comprehensive information on the distribution of N. annamensis and to clarify its boundaries with adjacent gibbon species.