The southern white-cheeked gibbon (''Nomascus siki'') is a species of

gibbon Gibbons () are apes in the family Hylobatidae (). The family historically contained one genus, but now is split into four extant genera and 20 species. Gibbons live in subtropical and tropical rainforest from eastern Bangladesh to Northeast India ...

native to

Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...

and

Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist ...

. It is closely related to the

northern white-cheeked gibbon The northern white-cheeked gibbon (''Nomascus leucogenys'') is a Critically Endangered species of gibbon native to South East Asia. It is closely related to the southern white-cheeked gibbon (''Nomascus siki''), with which it was previously con ...

(''Nomascus leucogenys'') and the

yellow-cheeked gibbon The yellow-cheeked gibbon (''Nomascus gabriellae''), also called the golden-cheeked gibbon, the yellow-cheeked crested gibbon, the golden-cheeked crested gibbon, the red-cheeked gibbon, or the buffed-cheeked gibbon, is a species of gibbon native ...

(''Nomascus gabriellae''); it has previously been identified as a subspecies of each of these.

Description and habitat

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 of ''N. leucogenys'', which has the white in a streak along the cheeks. Females have a thin edging of white around the face.Groves, Colin. ''Speciation and biogeography of Vietnam’s primates''. Vietnamese Journal of Primatology (2007) 1, 27-40
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The species lives in lowland broadleaf forest, with some populations living in forested mountainous areas. As with all gibbons, they are

arboreal Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...

and

frugivorous A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...

. The original distribution covered an area of central

and central

, ranging from the

Nam Theun Nam Theun (also known as ''Khading''), is a river in Laos, in Khammouane and Bolikhamsai Provinces. Together with its tributaries Nam One, Nam Noy, and Nam Theun it has total length of and drains an area of . "Nam Theun" is also three options ...

(Khading) and Rao Nay rivers in the north (approximately 19th parallel north) to the Banghiang and Thach Han rivers in the south (approximately 17th parallel north).Mootnick and Fan (2011). ''A Comparative Study of Crested Gibbons (Nomascus).'' American Journal of Primatology 73: 135–154Thinh, Mootnick, Thanh, Nadler and Roos (2010). ''A new species of crested gibbon, from the central Annamite mountain range.'' Vietnamese Journal of Primatology 4: 1-12 Between 19 and 20 parallel there appears to be an area of overlap or

intergradation In zoology, intergradation is the way in which two distinct subspecies are connected via areas where populations are found that have the characteristics of both. There are two types of intergradation: primary and secondary intergradation. Primary ...

between ''N. siki'' and ''N. leucogenys''. 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 as

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...

; it is legally protected in Vietnam, but this is not effectively enforced outside of protected areas. Hunting for food,

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...

and the pet trade is a serious threat to this species in both Laos and Vietnam.

Taxonomy

The

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

was first formally identified in 1951 by Jean Théodore Delacour where he described ''siki'' as a subspecies of '' N. concolor'' (a species placed in '' Hylobates'' at that time). Since its description, it has been considered to be a subspecies of variously '' N. leucogenys'', '' N. gabriellae'', or '' N. concolor''. The assignation of ''N. siki'' as a subspecies of ''N. gabriellae'' was due to the interpretation of a single baculum, but later research indicated that the specimen was part of a different species. It was then assigned to ''N. leucogenys'' due to similarities of its song, as well as strong visual similarities between the females of the two species. However, it has been considered a separate species since 2001. In the north of the range of ''N. siki'', it overlaps or intergrades with ''N. leucogenys'', and based on

mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DNA ...

and voices, these species are closer to each other than to the remaining ''

Nomascus ''Nomascus'' is the second-most speciose genus of gibbons (family Hylobatidae). Originally, this genus was a subgenus of ''Hylobates'', and all individuals were considered one species, ''Hylobates concolor''. Species within ''Nomascus'' are cha ...

''; some maintain that ''N. siki'' should be regarded as a subspecies of ''N. leucogenys''. A southern population formerly associated with ''N. siki'' was described as a new species, '' N. annamensis'' in 2010.

References

External links

Photograph gallery
{{Taxonbar, from=Q1365814

southern white-cheeked gibbon The southern white-cheeked gibbon (''Nomascus siki'') is a species of gibbon native to Vietnam and Laos. It is closely related to the northern white-cheeked gibbon (''Nomascus leucogenys'') and the yellow-cheeked gibbon (''Nomascus gabriellae'') ...

Primates of Southeast Asia Mammals of Laos Mammals of Vietnam Endangered fauna of Asia Species endangered by the pet trade

Taxa named by Jean Théodore Delacour