Gibbons represent a highly successful radiation of four genera and 20 species of Asian apes that, in response to recent habitat fragmentation and deforestation, are threatened with extinction. China has six species of gibbons, each of which is critically endangered. We present new biogeographical information on the distribution of the black crested gibbon (Nomascus concolor). Four subspecies of N. concolor have been described: three of them are present east of the Mekong River (Nomascus concolor jingdongensis, N. c. concolor and N. c. lu); and another is found west of the Mekong River (N. c. furvogaster). In addition, there has been speculation that gibbons exist in the Biluo Snow Mountains, between the Mekong and Salween basins. To clarify the biogeography of this species, from April 2011 to January 2012 and from January 2016 to September 2018, we conducted interviews with local villagers, completed line transect surveys, monitored gibbon calls, and placed 30 camera traps in the forest canopy. On October 30, 2016, we recorded gibbon's calls. On July 5, 2016, our camera traps obtained one image of a male gibbon, and on February 1 and 8, 2017, we captured two independent images of an adult female gibbon on Zhiben Mountains. Based on the black crest on the head, clearly visible in the photographs, the gibbons are N. c. furvogaster. Evidence from interviews and survey records indicate that N. c. furvogaster once was present in the Zhiben Mountains, at an altitude of between 2000 and 2700 m. Between 1990 and 2000, some 6-7 groups still existed in Caojian, Laowo and adjacent areas. Unfortunately, in the absence of an effective conservation strategy, the population was extirpated by hunters. The remaining forest in the Zhiben Mountains is highly fragmented, and most of the suitable habitat for gibbons has been lost. Therefore, we expect that this newly found gibbon population is under extreme anthropogenic pressure. It is imperative that further investigations of this gibbon population be conducted immediately, and that the local and national governments implement effective conservation plans, including educating the local communities to protect this critically endangered primate population.
Keywords: Biluo Snow Mountains; Camera trap; Nomascus concolor furvogaster; Northernmost distribution.