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Overview

Brief Summary

Biology

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 (4). Gibbons are also adept however, at walking upright, both on the ground and in the trees (2). Black-crested gibbons live in small family groups consisting of a monogamous male and female and their offspring, there are also reports that groups may contain additional mature females (4). These apes are predominantly arboreal and the group forages and sleeps amongst the trees (2). Led by the female, the breeding pair partakes in vigorous bouts of singing in the morning, which hauntingly echo through the forest. It is believed that these 'duets' are essential in pair bond formation and reinforcement, but also serve to advertise the presence of the group within the territory (2). A single young is born every two to three years and the infant is usually weaned once it reaches 2 years old (2). Black-crested gibbons feed preferentially on ripe sugar rich fruit such as figs (Ficus spp.), although they also supplement their diet with leaves and insects (2).
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Description

The black-crested gibbon is one of the world's most endangered primates and may be on the very brink of extinction (7). Males and females are strikingly different in appearance with males almost completely black, but sometimes with white or buff cheeks, and females a golden or buff colour with variable black patches, including a black streak on the head (2). The common name of this species comes from the tuft of longer fur on the crown of the head (5). Both sexes have the characteristic slender shape of the 'lesser ape' with long arms and legs, grasping hands and feet, and no tail (4). A variety of calls are produced, which are amplified with the aid of a throat sac below the chin; males and females engage in duets, in which males grunt, squeal and whistle whilst females sing rising notes and twitter (2).
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Distribution

Range Description

The species as a whole occurs discontinuously in southwestern China, northwestern Lao PDR and northern Viet Nam (Geissmann et al. 2000). One thousand years ago, gibbons that may have been crested gibbons (genus Nomascus ) were distributed over a large part of southern and central China up to the Yellow River (Geissmann 1995; Geissmann et al. 2000; van Gulik 1967).

Nomascus concolor concolor
This taxon occurs in southern China (southwestern Yunnan) and northern Viet Nam (Lao Cai, Yen Bai, Son La, and Lai Chau provinces) (Geissmann et al. 2000). It is found between the Song Da (Black) and Song Hong (Red) Rivers, north to 23°45?N and south to about 20°N (Groves 2001). Reported occurrences west of the Black River are unconfirmed (T. Geissmann pers. comm.).

Nomascus concolor furvogaster
This taxon occurs in southern China (southwestern Yunnan). It is found only in a small region near the Myanmar border, west of the Mekong River (23°15??23°40?N, 99°05??99°29?E) (Groves 2001).

Nomascus concolor jingdongensis
This taxon occurs in southern China (west-central Yunnan). It is found only in a small region around Wuliang Mountain, between the Mekong and Chuanhe rivers (about 24 to 25°N) (Groves 2001).

N. concolor lu
This taxon occurs in northwestern Lao PDR. An isolated population, it is known for certain only in a tiny area in on the east bank of the Mekong at about 20°17?? 20°25?N (Groves 2001). It is confirmed in Nam Ha National Protected Area, Luang Namtha province, and in the Nam Kan Provincial Protected Area, Bokeo province (Geissmann 2007; Johnson et al. 2005).
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Geographic Range

Black crested gibbons, Nomasus concolor, are primarily found in Yunnan, China and have restricted ranges in western Laos and northern Vietnam (Geissmann and Orgeldinger 2000). Their distribution is discontinuous, with populations occurring between the Black and Red Rivers in southern China (Nomascus concolor concolor), near the China-Myanmar border (Nomascus concolor furvogaster), between the Mekong and and Chuanghe Rivers (Nomascus concolor jingdongensis), and in northwestern Laos (Nomascus concolor lu) (Groves 2001).

Biogeographic Regions: oriental (Native )

  • Geissmann, T., M. Orgeldinger. 2000. The relationship between duet songs and pair bonds in siamangs, Hylobates syndactylus.. Animal Behaviour, 60: 805-809.
  • Groves, C. 2001. Primate Taxonomy. Washington, DC, USA: Smithsonian Institute Press.
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Range

The black-crested gibbon is found in South East Asia, and the greatly reduced and fragmented range includes Vietnam, China and Laos. Much confusion surrounds the taxonomy of this species but at present five different subspecies are recognised (9). The central Yunnan (Nomascus concolor jingdongensis) and the west Yunnan black-crested gibbon (N. c. furvogaster) are both found within the Yunnan Province of China (6). Whilst the Laotian black-crested gibbon (N. c. lu) is found in Laos, the Tonkin black-crested gibbon (N. c. concolor) is found in Northern Vietnam (7) and the Hainan black-crested gibbon (N. c. hainanus) is found on Hainan Island, China (6).
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Physical Description

Morphology

Physical Description

Male black crested gibbons are black, while females are a tawny buff color. Females have a black crown and typically have black hair grizzling or covering the lower chest and abdomen (Mootnick and Fan 2011). This sexual dichromatism develops with age, as the female changes from black to buff or tawny coloration in early adulthood (Mootnick and Fan 2011). Black crested gibbons generally weigh from 6.9 to 10 kg (average 8 kg) and measure between 43 and 54 cm (average 50 cm) (Ma et al. 1988).

Range mass: 6.9 to 10 kg.

Range length: 43 to 54 cm.

Sexual Dimorphism: sexes colored or patterned differently

  • Ma, S., Y. Wang, F. Poirier. 1988. Taxonomy, distribution and status of gibbons (Hylobates) in Southern China and adjacent areas. Primates, 29: 277-286.
  • Mootnick, A., P. Fan. 2011. A Comparative Study of Crested Gibbons (Nomascus). American Journal of Primatology, 73: 135-154.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
This species occurs in subtropical and montane evergreen, semi-evergreen and deciduous forest (Geissmann et al. 2000; Jiang et al. 2006). In China it is likely restricted to broadleaved evergreen forests (Geissmann et al. 2000). In Yunnan province, N. c. concolor and N. c. jingdongensis occur at altitudes ranging from 1,900 to 2,700 m (Bleisch and Chen 1991; Jiang et al. 2006), but at other sites in Yunnan the species may also occur at elevations as low as 500 m (Lan 1989a,b). In northern Viet Nam, the species was reported to occur at elevations of 1,600-2,000 m (Dao Van Tien 1983). A survey area in Nam Kan National Biodiversity Conservation Area, Lao PDR, covered an altitudes range of about 440?900 m, but gibbon habitat and gibbons mainly occurred at altitudes above 550 m (Geissmann 2007).

Most gibbon species are mainly frugivorous (Leighton 1987). Field studies on Chinese N. concolor, however, report a lower intake of fruits and flowers (Geissmann et al. 2000) as compared to most other gibbon species except siamangs. On Mount Wuliang (central Yunnan), N. concolor jingdongensis eat more fruit during the rainy season, whereas they eat a higher percentage of leaves and spend more time foraging during the dry season (Sheeran 1993, 1995).

Average group sizes for N. c. concolor and N. c. jingdongensis in Yunnan province also appear to vary strongly according to locality and/or study, ranging from 2.9 to 6.6 individuals (Chan et al. 2005), with a mean of 5.0 individuals (T. Geissmann pers. comm. 2006). This mean value is clearly higher than average group sizes found in other gibbon species (Leighton, 1987). It is unknown whether this high value applies to other populations of this species, such as N. c. lu in Lao PDR, N. c. furvogaster in western Yunnan or N. c. concolor in Viet Nam. Based on five groups of N. c. lu observed in Nam Kan PPA in Lao PDR, an average group size of 3.6?3.8 individuals was determined (Geissmann 2007).

Systems
  • Terrestrial
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Black crested gibbons live in evergreen, semi-evergreen, and deciduous forests in subtropical and mountainous areas (Geissmann and Orgeldinger 2000; Jiang et al. 2006). They are primarily observed at altitudes ranging from 2100 to 2400 m above sea level, where most of their food resources are concentrated (Fan and Jiang 2010). However, in Vietnam, black crested gibbons were observed living at altitudes from 1600 to 2000 m (Dao Van Tien 1985) and in Laos, from 550 to 900 m (Geissmann 2007). Black crested gibbons have been observed at altitudes as high as 2689 m (Fan and Jiang 2010).

Range elevation: 550 to 2689 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

  • Dao Van, T. 1985. Scientific results of some mammals surveys in North Vietnam (1957 - 1971). Ha Noi, Vietnam: Scientific and Technical Publishing House.
  • Fan, P., X. Jiang. 2010. Altitudinal ranging of black-crested gibbons at Mt. Wuliang, Yunnan: Effects of food distribution, temperature and human disturbance. Folia Primatologica, 81: 1-9.
  • Geissmann, T. 2007. First field data on the Laotian black crested gibbon (Nomascus concolor lu) of the Nam Kan area of Laos. Gibbons Journal, 3: 56-65.
  • Jiang, X., Z. Luo, S. Zhao, R. Li, C. Liu. 2006. Status and distribution pattern of black crested gibbon (Nomascus concolor jingdongensis) in Wuliang Mountains, Yunnan, China: implication for conservation. Primates, 47: 264-271.
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The black-crested gibbon inhabits tropical evergreen broad-leaved forests and semi-deciduous monsoon forests (4).
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Trophic Strategy

Food Habits

In Yunnan, China, black crested gibbons are folivorous-frugivorous, spending on average similar amounts of time eating leaves and fruit. Their diet varies seasonally, based on the availability of food sources including leaves, fruits, buds, and flowers. In a study in 2008 (Fan et al.), black crested gibbons ate increased levels of figs in August and September, flowers in February and April, leaves in March, and buds and leaves in December and January. They prefer to eat fruits and figs over other foods during their first and last meals of the day (Fan et al. 2008). They have also been observed eating insects, eggs, and other small organisms. One population of black crested gibbons concentrated ranging behavior, staying in valleys with more abundant food for several consecutive days before moving to another, in order to avoid frequent passages through areas with little food (Fan and Jiang 2008).

Animal Foods: birds; mammals; reptiles; eggs; insects

Plant Foods: leaves; fruit; flowers

Primary Diet: herbivore (Folivore , Frugivore )

  • Fan, P., X. Jiang. 2008. Effects of food and topography on ranging behavior of black crested gibbon (Nomascus concolor jingdongensis) in Wuliang Mountain, Yunnan, China. American Journal of Primatology, 70: 871-878.
  • Fan, P., Q. Ni, G. Sun, B. Huang, X. Jiang. 2008. Gibbons under seasonal stress: the diet of the black crested gibbon (Nomascus concolor) on Mt. Wuliang, Central Yunnan, China. Primates, 50: 37-44.
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Associations

Ecosystem Roles

Because they consume a considerable amount of fruit, black crested gibbons likely act as seed dispersers. They also act as hosts to a variety of nematodes, roundworms, and other parasites, including Dirofilaria digitata, Probstmayria gorillae, Streptopharagus pigmentatus, Streptopharagus sandgroundi, and Dipetalonema digitatum.

Ecosystem Impact: disperses seeds

Commensal/Parasitic Species:

  • Dirofilaria digitata
  • Probstmayria gorillae
  • Streptopharagus pigmentatus
  • Streptopharagus sandgroundi
  • Dipetalonema digitatum

  • Yamashita, J. 1963. Ecological Relationships between Parasites and Primates. Primates, 4: 2-96.
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Predation

Predation of black crested gibbons has not been well characterized.

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Life History and Behavior

Behavior

Communication and Perception

Black crested gibbons communicate through vocalizations, including calls and songs, as well as physical interactions and facial expressions. The songs of black crested gibbons may be used for a variety of purposes, including defense of resources and establishment of territories (Sun et al. 2011), as well as attracting mates and strengthening pair bonds (Geissmann and Orgeldinger 2000). Black crested gibbons sing both alone and in pairs. Duets are usually initiated by males from high locations, such as tall trees on hills. Duets may play a part in mate attraction or pair-bonding between mates, defense of resources or mates, or group cohesion (Fan et al. 2009).

Communication Channels: visual ; tactile ; acoustic

Other Communication Modes: duets

Perception Channels: visual ; acoustic

  • Sun, G., B. Huang, Z. Guan, T. Geissmann, X. Jian. 2011. Individuality in Male Songs of Wild Black Crested Gibbons (Nomascus concolor). American Journal of Primatology, 73: 431-438.
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Life Expectancy

Lifespan/Longevity

Black crested gibbons are believed to have similar longevity to other gibbons, which is estimated to be 25 to 30 years.

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Lifespan, longevity, and ageing

Maximum longevity: 46.1 years (captivity) Observations: One specimen of the subspecies *gabriellae* lived 46.1 years in captivity (Richard Weigl 2005).
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Reproduction

Black crested gibbons live in family units generally consisting of a monogamous male and female and their offspring. Although most black crested gibbons are monogamous, occasionally two females in a single breeding group are tolerated (Jiang et al. 1999). Polygyny has not been observed in other species of gibbons.

Singing may play a role in mate attraction, pair-bonding, and mate defense of black crested gibbons (Geissmann and Orgeldinger 2000; Fan et al. 2009).

Mating System: monogamous ; polygynous

Black crested gibbons reproduce once every 2 to 3 years, usually producing one offspring in each interval. The gestation period lasts about 7 to 8 months, and newborns weigh about 510 g at birth (Geissmann and Orgeldinger 1995). Offspring are weaned around 2 years of age, and they reach sexual maturity at about 8 years of age.

Breeding interval: Black crested gibbons reproduce once every 2 to 3 years.

Average number of offspring: 1.

Range gestation period: 7 to 8 months.

Average birth mass: 510 g.

Average age at sexual or reproductive maturity (female): 8 years.

Average age at sexual or reproductive maturity (male): 8 years.

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Young black crested gibbons are nursed by their mother until about 2 years of age. Males and older offspring also provide care to young.

Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

  • Fan, P., W. Xiao, S. Huo, X. Jiang. 2009. Singing behavior and singing functions of black-crested gibbons (Nomascus concolor jingdongensis) at Mr. Wuliang, Central Yunnan, China.. American Journal of Primatology, 71: 539-547.
  • Geissmann, T., M. Orgeldinger. 1995. Neonatal Weight in Gibbons (Hylobates spp.). American Journal of Primatology, 37: 179-189.
  • Geissmann, T., M. Orgeldinger. 2000. The relationship between duet songs and pair bonds in siamangs, Hylobates syndactylus.. Animal Behaviour, 60: 805-809.
  • Jiang, X., Y. Wang, Q. Wang. 1999. Coexistence of Monogamy and Polygyny in Black-crested gibbon (Hylobates concolor). Primates, 40: 607-611.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
CR
Critically Endangered

Red List Criteria
A2cd

Version
3.1

Year Assessed
2008

Assessor/s
Bleisch, B., Geissmann, T., Timmins, R.J. & Xuelong, J.

Reviewer/s
Mittermeier, R.A. & Rylands, A.B. (Primate Red List Authority)

Contributor/s

Justification
The species is listed as Critically Endangered as there is an estimate of over 80% decline in the last 45 years (3 generations) due primarily to hunting and habitat loss.

History
  • 2000
    Endangered
  • 1996
    Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Indeterminate
    (IUCN Conservation Monitoring Centre 1986)
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Black crested gibbons are considered critically endangered by the IUCN (2010). Deforestation due to the steel industry, military activity during political unrest, and later to farming has greatly reduced viable habitat, threatening populations of black crested gibbons (Jiang et al. 2006). Although forests have been allowed to regenerate in some areas, in many others, farming has become permanent or invasive plant species have prevented forest regeneration (Jiang et al. 2006). Additionally, separation of small groups of this species due to habitat destruction may lead to decreased gene flow, further endangering the species (Jiang et al. 2006).

Hunting contributed to the extirpation of black crested gibbons in areas of Wuliang (Jiang et al. 2006). Although no reports of poaching have occurred since 1994, even low rates of hunting are projected to carry the risk of local extinction (Seal 1994).

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: critically endangered

  • Bleisch, B., T. Geissmann, R. Timmins, J. Xuelong. 2008. "Nomascus concolor. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4" (On-line). Accessed April 25, 2011 at http://www.iucnredlist.org/apps/redlist/details/39775/0.
  • Seal, U. 1994. Thai gibbon life history and vortex analysis. Pp. 23-36 in S Tnhkorn, W Brockelman, R Tilson, U Nimmanheminda, P Ratanakorn, R Cook, A Teare, K Castle, U Seal, eds. Thai gibbon population and habitat viability analysis. Thailand: Khao Yai.
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Status

Classified as Endangered (EN) on the IUCN Red List 2006 (1), and listed on Appendix I of CITES (3). Subspecies: Tonkin black-crested gibbon (Nomascus concolor concolor) classified as Endangered (EN A1cd, C2a); West Yunnan black-crested gibbon (N. c. furvogaster) Critically Endangered (CR A2cd, B2a); Central Yunnan black-crested gibbon (N. c. jingdongensis) Critically Endangered (CR C2b); Laotian black-crested gibbon (N. c. lu) Endangered (EN A1c) (1); Hainan black-crested gibbon (N. c. hainanus) is Critically Endangered (EN), numbering fewer than 20 individuals (9).
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Population

Population
The global population is estimated at approximately 1,300-2,000 individuals (T. Geissmann pers. comm.2006). There are known declines and local population extinctions throughout the species? range (Geissmann et al. 2000, 2003; Ni and Ma 2006). The overall rate of decline is extremely severe.

Density estimates for N. c. concolor and N. c. jingdongensis in Yunnan province (China) range from 0.43 to 0.82 groups/km2 (Chan et al. 2005), with a mean of 0.6 groups/km2 (Geissmann pers. comm. 2006). Using an average group size of 5.0 individuals, this would translate into a density of about 3 individuals/km2 (T. Geissmann pers. comm. 2006). For N. c. lu in Lao PDR, a short survey covering an area of 20 km2 in the Nam Kan National Biodiversity Conservation Area suggests a density of 0.45 groups/km2 or 1.6 individuals/km2, using a more conservative average group size of 3.4 individuals (T. Geissmann pers. comm. 2006).

Population estimates for the Chinese portion of this species range from about 200 to 260 groups (Jiang et al. 2006). Using an average group size of 5.0 individuals, this would translate into 1,000 to 1,300 individuals. Perhaps the most important subpopulation in China resides in the Wuliang Mountains and numbers about 100 groups (Jiang et al. 2006). There are 98 groups of N. c. jingdongensis (Jiang et al. 2006), with a total of about 490 individuals, if an average groups size of 5 individuals is used. For N. c. furvogaster there are about 26-42 groups remaining (Jiang et al. 2006), which would represent about 130-210 individuals, if an average groups size of 5 individuals is used. A survey in the northern part of Ailao Mountain National Nature Reserve found approximately 45 groups of N. c. concolor, with around 200-250 individuals (X. Jiang pers. comm. 2006). In southern Yunnan there are three areas where this species occurs, in Bajiaohe, Jingping County (2 groups recorded), Jinpingfenshuiling Nature Reserve (only one group recorded), and Huanglianshan Nature Reserve (3 groups recorded) (Ni and Ma 2006). The total population in Yunnan was reported to be 74-106 groups (Jiang et al. 2006), which translates to about 370-530 individuals, if an average groups size of 5 individuals is used.

The Laotian population in the Nam Kan PPA is small. At least 13 distinct groups were recorded in the Nam Kan valley in a survey area of about 6 km2, suggesting a density of about 2.2 groups/km2 (Geissmann 2007). The total population of the Nam Kan could be up to 200 individuals, although this is a very tentative extrapolation (T. Geissman pers. comm. 2006). Five groups were recorded from Nam Ha NPA (Johnson et al. 2005), but there is no population estimate. There are forest blocks in northern Lao PDR where there have not been any surveys for gibbons, and there could be populations in these areas.

In Viet Nam, field surveys carried out by Fauna and Flora International throughout most of the remaining larger forest areas in the historic range of the species in Viet Nam lead to an estimate of less then 100 individuals. The two largest populations may live in Che Tao and Ho Nam Mu forests (Yen Bai and Son La provinces) with about 70 and 20 individuals, respectively (Geissmann et al. 2000). As of 2000, N. concolor in Viet Nam has been confirmed in Nam Pam commune of Muong La District in Son La Province with 15-20 individuals (Tri and Long 2000). This is probably the same population that survives in Che Tao commune of Mu Cang Chai district in Yen Bai Province (Tallents et al. 2000). Another population has been confirmed in Nam Xe commune of Van Ban District in Lao Cai Province. This commune borders Yen Bai Province as well, to the north (Dat et al. 2000). There are known subpopulation extinctions in Viet Nam (Geissmann et al. 2000).

Population Trend
Decreasing
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Threats

Major Threats
The biggest threats to Nomascus concolor throughout its range include destructive local forest use and hunting (Geissmann et al. 2000; Jiang et al. 2006). In Lao PDR, despite the presence of local taboos on hunting gibbons (Geissmann 2007), these animals are captured and killed for subsistence as well as the pet and ?medicine? trades (Johnson et al. 2005). In Viet Nam, depending on the locality, these gibbons are threatened by mostly human impact on habitat (Van Ban, Lao Cai Province) or mostly hunting pressure (Mu Cang Chai, Yen Bai Province and Son La Province), but it is ultimately always a combination of the two (Geissmann et al. 2000; Tallents et al. 2000a, 2000b, 2001a, 2001b; Le Trong Dat et al. 2000, 2001; Ngo Van Tri and Long 2000).
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Deforestation has swept across South East Asia at an alarming rate as trees are logged for timber or to make way for agriculture and development. Gibbons throughout the region have undergone dramatic declines due principally to this habitat loss, but also as a result of hunting (7). The fragmentation of their habitat causes groups to become separated from the remaining population (2), and it is estimated that about 75% of the black crested gibbon's original habitat has already been lost (8). The taxonomic confusion surrounding this species makes population estimates particularly difficult but at least two of the subspecies are today at critically low levels (1).
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Management

Conservation Actions

Conservation Actions
This species is listed on CITES Appendix I. In China, about three-quarters of the Wuliang Mountain population?s range is protected, much of it within the Wuliang Mountain Nature Reserve and Ailao Mountain Nature Reserve; the species occurs as well in Huanglianshan Nature Reserve, Fenshuilin Nature Reserve, Daxueshan Nature Reserve, Nanguanhe Nature Reserve, Lancangjiang Nature Reserve (Geissmann et al. 2000). In Lao PDR it occurs in two protected areas, Nam Ha National Biodiversity Conservation Area and Nam Kan National Biodiversity Conservation Area. The provincial governor of Luang Namtha province (Lao PDR) in 2004 set very steep fines for wildlife trade and also instigated measures for gun control; both actions, if enforced, should protect the Laotian gibbon populations from opportunistic hunting (Johnson et al. 2005).
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Conservation

The black-crested gibbon is protected from international trade by its listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) (3). Fauna and Flora International (FFI) have been studying the species in Northern Vietnam since 1999. They have also been involved in a community awareness programmes in the area and there is pressure to designate the last stronghold of the species (the Che Tao Forest) as a Gibbon Sanctuary (7). In China, the largest population of the Central Yunnan black crested gibbon subspecies occurs within the Wuliang Mountain National Reserve (7). It is vital that any remaining viable populations and habitats are protected or this previously successful ape is in grave danger of disappearing.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

There are no known adverse effects of black crested gibbons on humans.

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Economic Importance for Humans: Positive

Black crested gibbons can be found in some zoos worldwide. Although now restricted, hunting once contributed considerably to the decline of black crested gibbons.

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Wikipedia

Black crested gibbon

The black crested gibbon (Nomascus concolor) is an endangered species of gibbon found in China, Laos, and northern Vietnam, with four subspecies.

Taxonomy[edit]

The taxonomy of the species is confused. Previously grouped in the Hylobates genus, currently four subspecies are recognised.[2]

  • Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), Yunnan 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

Physical characteristics[edit]

The length from the head to the end of body is 43–54 cm (17–21 in) and it weighs from 6.9 to 10 kg (15 to 22 lb).[3] The species exhibits sexual dichromatism, the male is almost completely black, but sometimes with white or buff cheeks, while the female is a golden or buff colour with variable black patches, including a black streak on the head.[3]

Behavior[edit]

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[edit]

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.[4] 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.[5] 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,[5] 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.[6] Social behaviors within groups will evolve according to Hamilton’s rule.[7]

Mating[edit]

Gibbons were previously reported to practice monogamous sexual relationships.[5] They are known to form pair bonds, as well documented in the majority of gibbon species.[6] 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.[4] 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.[4] 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.”[4] 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.[4] This hypothesis is supported by the large scrotal size allowing for increased sperm production.[4] Other observations have been made that males will share child carrying to place less of a burden on the female, delaying her interbirth time.[5] The conflicting observations support the hypothesis that black-crested gibbons demonstrate both monogamous and polygamous sexual relationships.

Singing[edit]

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.[8] The songs are innately altruistic, as each group calls separately.

Distribution and habitat[edit]

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.[2]

The four subspecies are geographically separated. The Tonkin black crested gibbon (Nomascus concolor concolor) occurs in southern China (southwestern Yunnan) and northern Vietnam (Lào Cai, Yên Bái, Sơn La, and Lai Châu provinces), between the Black and Red Rivers. The west Yunnan black crested gibbon (N. c. furvogaster) occurs in a small area near the Burma 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 Mountain, 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.[2]

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.[3]

Conservation[edit]

The black crested gibbon is listed as critically endangered on the IUCN Red List. An estimated 1300 to 2000 individuals are left in the wild.[2]

References[edit]

  1. ^ Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. p. 180. OCLC 62265494. ISBN 0-801-88221-4. 
  2. ^ a b c d e Bleisch, B., Geissmann, T., Timmins, R. J. & Xuelong, J. (2008). Nomascus concolor. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
  3. ^ a b c Cheng, Clarence (2011). Sargis, Eric; McCormick, Gale, eds. "Nomascus concolor". Animal Diversity Web. Retrieved 29 December 2011. 
  4. ^ a b c d e f Jiang, Xuelong, Yingxiang Wang, and Qiang Wang. “Coexistence of Monogamy and Polygyny in Black-crested Gibbon (Hylobates concolor).” Primates, 40(4): 607-611.
  5. ^ a b c d Brockelman, Warren Y. “Ecology and the Social Systems of Gibbons. The Gibbons Developments in Primatology: Progress and Prospects. 211-239. 2009
  6. ^ a b Silk, Joan B. “Kin Selection in Primate Groups.” International Journal of Primatology. Vol. 23, No. 4, August 2002.
  7. ^ Silk, Joan B. “Practicing Hamilton’s rule: kin selection in primate groups.” Cooperation in Primates and Humans: Mechanisms and Evolution. 2006.
  8. ^ 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.
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