Silvery gibbon

The silvery gibbon (Hylobates moloch), also known as the Javan gibbon, is a primate in the gibbon family Hylobatidae. It is endemic to the Indonesian island of Java, where it inhabits undisturbed rainforests up to an altitude of 2,450 m (8,040 ft). It is listed as Endangered on the IUCN Red List since 2008, as the wild population is estimated at comprising less than 2500 mature individuals.[1]

Silvery gibbon
A silvery gibbon foraging in a Ficus tree. Photograph taken in Mount Halimun Salak National Park
CITES Appendix I (CITES)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hylobatidae
Genus: Hylobates
Species:
H. moloch[2]
Binomial name
Hylobates moloch[2]
(Audebert, 1798)
Silvery gibbon range

Its coat is bluish-grey in colour, with a dark grey or black cap. Like all gibbons, the silvery gibbon lacks an external tail, has dorsally placed scapulae, and reduced flexibility in its lumbar region. It has long, curved fingers and very long forelimbs relative to its hind limbs. On average, it reaches 8 kg (18 lb) in weight. It is diurnal and arboreal, climbing trees skilfully and brachiating through the forests. Brachiation is possible because of its mobile wrist joints, full rotation of the upper arm, and the ability to lock elbows in suspension. Its diet consists of fruits, leaves, and flowers.

Every three years, on average, the female gives birth to a single young, after a gestation of seven months. The offspring is nursed for about 18 months and lives with the family group until it is fully mature at about eight to ten years old.[3]

Threats and conservation

The silvery gibbon ranks among the most threatened primates. It is listed as Endangered on the 2009 IUCN Red List,[1] with the population appearing more stable than in a 2004 assessment of the species being Critically Endangered, which suggested there was a 50% chance of the silvery gibbon becoming extinct within the next decade.[4] Habitat destruction on densely populated Java continues to reduce the natural range of the species. Many gibbons are also lost to the illegal pet trade, when adults are hunted so their young can be sold in the markets as pets.[4] There are less than 2,000 silvery gibbons in the wild on eight sites that are considered to be genetically viable for the continuation of the species. There are also a dozen small, non-viable populations. Mount Halimun Salak National Park sustains the largest population of ca. 1,000 gibbons.[4] Other large populations of several hundred are found in the Gunung Ciremai National Park and Gunung Gede Pangrango National Park.[5] In the latter there is a Javan Gibbon Centre that rehabilitates ex-captive gibbons.[6]

Several zoos operate silvery gibbon breeding programs. Despite these efforts, the future survival of this species is in question.

Behaviour and ecology

Like all gibbon species, the silvery gibbon lives in pairs and stakes out territory that the pair strongly defends; it has relatively small territories of about 42 acres. Females sing to declare their territory several times a day, and if strangers are spotted, the male screams loudly in an attempt to scare them away. The majority of the solo song bouts or scream bouts are produced by the females.[7] The female vocal bouts occur after 0500 hr, with the vocal bout activity peaking around 0600 hr. In contrast, the male vocal bouts primarily occur before 0500 hr.[7] The males are usually very aggressive to others.

Classification

Some authors recognize two subspecies of Hylobates moloch:[8]

  • Western silvery gibbon or western Javan gibbon, H. m. moloch
  • Eastern silvery gibbon or central Javan gibbon, H. m. pongoalsoni

References
  1. Nijman, V. (2020). "Hylobates moloch". IUCN Red List of Threatened Species. 2020: e.T10550A17966495. doi:10.2305/IUCN.UK.2020-2.RLTS.T10550A17966495.en. Retrieved 17 January 2022.
  2. Groves, C. P. (2005). "Species Hylobates moloch". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 180. ISBN 0-801-88221-4. OCLC 62265494.
  3. Kappeler, M. (1981). The Javan silvery gibbon (Hylobates lar moloch), habitat, distribution, numbers (Ph.D.). Basel: University of Basel.
  4. "The Silvery Gibbon Project". Retrieved 2007-12-11.
  5. Supriatna, Jatna. "Conservation Programs for the Endangered Javan Gibbon" (PDF). Primate Conservation. 2006 (21): 155–162.
  6. The Silvery Gibbon Project: "Conservation Projects" Archived 2013-12-20 at archive.today, retrieved 20 December 2013
  7. Geissmann, T.; Nijman, V. (2009). "Calling in Wild Silvery Gibbons (Hylobates moloch) in Java (Indonesia): Behavior, Phylogeny, and Conservation". American Journal of Primatology. 68 (1): 1–19. doi:10.1002/ajp.20203. PMID 16419119. S2CID 5900145.
  8. Geissmann, T. "Gibbon Systematics and Species Identification". Retrieved 2006-04-13.
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