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The black crested gibbon (''Nomascus concolor'') is a Critically Endangered species of gibbon found in China, Laos, and northern
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 it ...
, with four subspecies.


Taxonomy

The taxonomy of the species is confused. Previously grouped in the genus '' Hylobates'', currently four subspecies are recognised. *Central Yunnan black crested gibbon (''Nomascus concolor jingdongensis''),
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
province, China *West Yunnan black crested gibbon (''N. c. furvogaster''), Yunnan province, China *Laotian black crested gibbon (''N. c. lu''), Laos *Tonkin black crested gibbon (''N. c. concolor''), northern Vietnam


Description

The length from the head to the end of body is and it weighs from . The species exhibits
sexual dichromatism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
, the male is completely black, while the female is a golden or buff colour with variable black patches, including a black streak on the head.


Behavior

Gibbons are forest dwellers and are well known for their habit of swinging between the branches of the rainforest on their long arms, a method of locomotion known as brachiation. Gibbons are also adept, however, at walking upright, both on the ground and in the trees. Black crested gibbons live in small family groups consisting of a monogamous male and female and their offspring; occasionally groups reportedly may contain additional mature females. These apes are predominantly arboreal and the group forages and sleeps amongst the trees. Led by the female, the breeding pair partakes in vigorous bouts of singing in the morning, which hauntingly echo through the forest. These 'duets' are believed to be essential in pair bond formation and reinforcement, and also serve to advertise the presence of the group within the territory. A single young is born every two to three years and the infant is usually weaned once it reaches two years old; Black crested gibbons feed preferentially on ripe, sugar-rich fruit, such as figs, but occasionally consume vitamin-rich leaf buds, and rarely eat animals.


Group living

Black-crested gibbons live arboreally in small groups, most of which consist of a pair of adults, one male and one female, and their offspring. It has been observed that some groups consist of one adult male living with two to four females and their offspring. The group could potentially include one infant, one juvenile, one adolescent, and one sub adult.Jiang, Xuelong, Yingxiang Wang, and Qiang Wang. "Coexistence of Monogamy and Polygyny in Black-crested Gibbon (Hylobates concolor).” Primates, 40(4): 607-611. Groups have been found to be territorial, like other species of gibbons. Territories are limited by the availability of the male for territory defense. Thus, group and territory size would be limited. With a large group, territory defense would not be favored by kin selection due to the group consisting of less-closely related individuals.Brockelman, Warren Y. "Ecology and the Social Systems of Gibbons. The Gibbons Developments in Primatology: Progress and Prospects. 211-239. 2009 Though the research is not explicit, there can be some assumptions made about altruism within groups. Since the majority of groups are living in monogamous relationships with both males and females displaying aggression when another individual enters, it is likely that kin selection plays a major role in determining behavior of the group. Kin recognition is thought to be favored for maternal-offspring relationships. This is largely due to primates' uncertainty over paternity, even in pair-bonding species due to female promiscuity.
Silk, Joan B. Joan B. Silk (born December 16, 1953) is an American primatologist, Regents Professor in the School of Human Evolution and Social Change (SHESC) at Arizona State University . Her research interests include evolutionary anthropology, animal beh ...
"Kin Selection in Primate Groups". International Journal of Primatology. Vol. 23, No. 4, August 2002.
Social behaviors within groups will evolve according to Hamilton's rule.Silk, Joan B. "Practicing Hamilton’s rule: kin selection in primate groups". Cooperation in Primates and Humans: Mechanisms and Evolution. 2006.


Mating

Gibbons were previously reported to practice monogamous sexual relationships. They are known to form pair bonds, as well documented in the majority of gibbon species. Upon the discovery of single male, multi-female living groups, the question arose to determine if all females were mating. The observation that offspring of similar ages lived within a multi-female group confirmed that polygyny did in fact occur. The current hypothesis remains that both monogamous and polygamous relationships exist. There may be various selection pressures for polygyny within previously monogamous groups. Parents tend to be hostile towards maturing offspring, with males leaving the group more quickly than females do. Yet, upon tolerance by the mother, adult female offspring may remain in the group, as the group continues to forage and feed as family members. The mutual tolerance of females is likely to be caused by "weak territoriality of females". Further selection occurs due to the birth interval for a single female averaging 2–2.5 years. Male fitness would benefit from inseminating other females during a birth interval. This hypothesis is supported by the large scrotal size allowing for increased sperm production. Other observations have been made that males will share child carrying to place less of a burden on the female, delaying her interbirth time. The conflicting observations support the hypothesis that black-crested gibbons demonstrate both monogamous and polygamous sexual relationships.


Singing

All gibbon species are known to produce loud and long song bouts, lasting for 10–30 minutes. The black-crested gibbon sings in the morning, sometimes in duets initiated by the male. The males choose the highest tree branches, often near ridges. The songs are thought to be used for resource defense, mate defense, pairbonding, group cohesion and mate attraction.Fan, Peng-Fei, Wen Xiao, Sheng Huo, and Xue-Long Jiang. "Singing Behavior and Singing Functions of Black-Crested Gibbons at Mt. Wuliang, Central Yunnan, China". American Journal of Primatology. Vol 71: 539-547. 2009.


Distribution and habitat

The black crested gibbon has a discontinuous distribution across southwestern China, northwestern Laos, and northern Vietnam. One thousand years ago, gibbons which may have been crested gibbons (''Nomascus'') were found over a large part of southern and central China up to the
Yellow River The Yellow River or Huang He (Chinese: , Mandarin: ''Huáng hé'' ) is the second-longest river in China, after the Yangtze River, and the sixth-longest river system in the world at the estimated length of . Originating in the Bayan ...
. The four subspecies are geographically separated. The Tonkin black crested gibbon (''Nomascus concolor concolor'') occurs in southern China (southwestern
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
) and northern Vietnam ( Lào Cai, Yên Bái, Sơn La, and Lai Châu provinces), between the
Black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...
and Red Rivers. The West Yunnan black crested gibbon (''N. c. furvogaster'') occurs in a small area near the
Burma Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
border, west of the Mekong, in southwestern Yunnan, southern China. The Central Yunnan black crested gibbon (''N. c. jingdongensis'') occurs in a small region around the Wuliang Mountains, between the Mekong and Chuanhe rivers in west-central Yunnan. The Laotian black crested gibbon (''N. c. lu'') occurs in northwestern Laos in an isolated population on the east bank of the Mekong in Laos. The black crested gibbon inhabits tropical evergreen, semievergreen, deciduous forests in subtropical and mountainous areas. It generally lives in high altitudes, from 2100 to 2400 m above sea level, where most of their food resources are concentrated. In Vietnam and Laos, the species is found at lower altitudes, while in China, it has been observed as high as 2689 meters.


Conservation

The black crested gibbon is listed as critically endangered on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
. An estimated 1300 to 2000 individuals are left in the wild.


References


External links


ARKive
information page

{{Taxonbar, from=Q286483 black crested gibbon Primates of East Asia Primates of Southeast Asia Mammals of China Mammals of Laos Mammals of Vietnam Critically endangered fauna of Asia Species endangered by use as food Species endangered by human consumption for medicinal or magical purposes Species endangered by logging Species endangered by the pet trade black crested gibbon Taxa named by Richard Harlan