Southern White-cheeked Gibbon
Encyclopedia
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); it has previously been identified as a subspecies of each of these, and may potentially be a hybrid of the two rather than a separate species in its own right.
The species lives in lowland broadleaf forest, with some populations living in forested mountainous areas. As with all gibbons, they are arboreal and frugivorous.
The habitat covers an area of central Vietnam
and in southern Laos
, ranging between 17 and 19 degrees north latitude. Between 19 and 20 degrees there is an area of overlap inhabited by both N. siki and N. leucogenys; south of 17 degrees was traditionally believed to contain populations of N. siki, but is now thought to contain only N. gabriellae.
The species is widespread throughout its range 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; it is legally protected in Vietnam, but this is not effectively enforced outside of protected areas.
. It had previously been considered to be a subspecies of variously N. leucogenys, N. gabriellae
or N. concolor. The original 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.
There are some indications that the species may be a hybrid of N. leucogenys and N. gabriellae; it occupies a range sited between the two populations, and there are reports of N. siki interbreeding with N. gabriellae. To further complicate the issue, in the north of its range, the population mingles with that of N. leucogenys, whilst in the south, there is a large area where the population phenotypically resembles
N. gabriellae but has a song distinct from the main population of either species. These latter group are currently classed as N. gabriellae.
Gibbon
Gibbons are apes in the family Hylobatidae . The family is divided into four genera based on their diploid chromosome number: Hylobates , Hoolock , Nomascus , and Symphalangus . The extinct Bunopithecus sericus is a gibbon or gibbon-like ape which, until recently, was thought to be closely related...
native to Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
and Laos
Laos
Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...
. It is closely related to the northern white-cheeked gibbon (Nomascus leucogenys) and the yellow-cheeked gibbon
Yellow-cheeked Gibbon
The yellow-cheeked gibbon , also called the yellow-cheeked crested gibbon, the golden-cheeked crested gibbon or the buffed-cheeked gibbon, is a species of gibbon native to Vietnam, Laos and Cambodia....
(Nomascus gabriellae); it has previously been identified as a subspecies of each of these, and may potentially be a hybrid of the two rather than a separate species in its own right.
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.The species lives in lowland broadleaf forest, with some populations living in forested mountainous areas. As with all gibbons, they are arboreal and frugivorous.
The habitat covers an area of central Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
and in southern Laos
Laos
Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...
, ranging between 17 and 19 degrees north latitude. Between 19 and 20 degrees there is an area of overlap inhabited by both N. siki and N. leucogenys; south of 17 degrees was traditionally believed to contain populations of N. siki, but is now thought to contain only N. gabriellae.
The species is widespread throughout its range 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; it is legally protected in Vietnam, but this is not effectively enforced outside of protected areas.
Taxonomy
The species was first formally identified in 1951 by Jean Théodore DelacourJean Théodore Delacour
Jean Théodore Delacour was an American ornithologist of French origin. He was renowned for not only discovering but also rearing some of the rarest birds in the world...
. It had previously been considered to be a subspecies of variously N. leucogenys, N. gabriellae
Yellow-cheeked Gibbon
The yellow-cheeked gibbon , also called the yellow-cheeked crested gibbon, the golden-cheeked crested gibbon or the buffed-cheeked gibbon, is a species of gibbon native to Vietnam, Laos and Cambodia....
or N. concolor. The original assignation of N. siki as a subspecies of N. gabriellae was due to the interpretation of a single baculum
Baculum
The baculum is a bone found in the penis of most mammals. It is absent in humans, but present in other primates, such as the gorilla and chimpanzee.The bone aids in sexual intercourse.-Purpose:...
, 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.
There are some indications that the species may be a hybrid of N. leucogenys and N. gabriellae; it occupies a range sited between the two populations, and there are reports of N. siki interbreeding with N. gabriellae. To further complicate the issue, in the north of its range, the population mingles with that of N. leucogenys, whilst in the south, there is a large area where the population phenotypically resembles
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
N. gabriellae but has a song distinct from the main population of either species. These latter group are currently classed as N. gabriellae.