| Southern white-cheeked gibbon[1] | |
|---|---|
 | |
| Female (left) and male | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Family: | Hylobatidae |
| Genus: | Nomascus |
| Species: | N. siki |
| Binomial name | |
| Nomascus siki (Delacour, 1951) | |
 | |
| Southern white-cheeked gibbon range | |
Thesouthern white-cheeked gibbon (Nomascus siki) is a species ofgibbon, native toVietnam andLaos. It is closely related to thenorthern white-cheeked gibbon (Nomascus leucogenys) and theyellow-cheeked gibbon (Nomascus gabriellae); it has previously been identified as a subspecies of each of these.
Members of the species are not a uniform colour; unweaned juveniles are a light brown, turning to black after weaning. Adult males remain black, but adult females are brown. The name of the species is taken from the male's facial markings, a large patch of white fur around the edge of the mouth - this distinguishes it from a male ofN. leucogenys, which has the white in a streak along the cheeks. Females have a thin edging of white around the face.[4]
The species lives in lowland broadleaf forest, with some populations living in forested mountainous areas. As with all gibbons, they arearboreal andfrugivorous.[2]
The original distribution covered an area of centralVietnam and centralLaos, ranging from theNam Theun (Khading) andRao Nay rivers in the north (approximately19th parallel north) to theBanghiang andThach Han rivers in the south (approximately17th parallel north).[5][6] Between 19 and 20 parallel there appears to be an area of overlap orintergradation betweenN. siki andN. leucogenys.[2]
Within its original distribution, the species is still common in the remaining large forest blocks in Laos, but in Vietnam the populations are scattered due to human encroachment on their habitat for logging and farming. Numbers are thought to have declined by 50% over the last 45 years, and the species is classed asendangered; it is legally protected in Vietnam, but this is not effectively enforced outside of protected areas.[2] Hunting for food,traditional medicine and the pet trade is a serious threat to this species in both Laos and Vietnam.[2]
Thetaxon was first formally identified in 1951 byJean Théodore Delacour where he describedsiki as a subspecies ofN. concolor (a species placed inHylobates at that time). Since its description, it has been considered to be a subspecies of variouslyN. leucogenys,N. gabriellae, orN. concolor.[2] The assignation ofN. siki as a subspecies ofN. gabriellae was due to the interpretation of a singlebaculum, but later research indicated that the specimen was part of a different species. It was then assigned toN. leucogenys due to similarities of its song, as well as strong visual similarities between the females of the two species.[7] However, it has been considered a separate species since 2001.[1]
In the north of the range ofN. siki, it overlaps or intergrades withN. leucogenys,[2] and based onmtDNA and voices, these species are closer to each other than to the remainingNomascus; some maintain thatN. siki should be regarded as a subspecies ofN. leucogenys.[5][6] A southern population formerly associated withN. siki was described as a new species,N. annamensis in 2010.[6]
