Molochs, Hylobates moloch, are endemic to the Indonesian island of Java.
Biogeographic Regions: oriental (Native )
Other Geographic Terms: island endemic
Adult molochs weigh on average 8 kg. There is no apparent sexual dimorphism (size or color difference) between males and females. Both male and female are a silverly-gray color and possess a dark gray cap. Molochs have long arms and lean bodies, both of which are especially important while they are manuvering through the canopy of the rainforest.
Range mass: 4 to 9 kg.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Habitat and Ecology
The species is strictly arboreal and diurnal, and mainly frugivorous (Kappeler 1981, 1984). Home ranges in Ujung Kulon cover about 17 ha (Kappeler 1981, 1984). Inter-birth intervals in wild gibbons are typically 3-3.5 years (Leighton 1987; Palombit 1992), and age of sexual maturity and/or the age of dispersal in wild gibbons is about 8-10 years (Brockelman et al. 1998; Geissmann 1991), but the age at first reproduction may be about 10-12 years (Brockelman et al. 1998)
Gibbons live in the tropical rainforests and semi-evergreen rainforests of South and Southeast Asia. Hylobates moloch is found in the tropical rainforest in Java. It is found in the upper canopy of the lowland and hill forests. Gibbons spend most of their lives in trees, and rarely descend to the forest floor.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest
Along with other gibbon species, H. moloch is frugivorous, feeding on ripe fruits in the upper canopy of the tropical rainforests. Molochs have also been observed eating leaves and flowers. Being frugivorous poses certain problems because fruit patches are found in small, scattered areas throughout the rainforest. Gibbons have adopted a rapid form of locomotion, brachiation, in which they swing by their long arms from branch to branch. This rapid form of locomotion helps gibbons to travel rapidly and effeciently from one food source to another.
Plant Foods: leaves; fruit; flowers
Primary Diet: herbivore (Frugivore )
The role these primates play in their ecosystem has not been detailed in the literature. However, it is likely that through their frugivory, they play some role in seed dispersal.
Ecosystem Impact: disperses seeds
Details on predation of these animals are not available. However, we can speculate that because they use the high canopy of the rainforest, where branches might support the weight of large animals, their predators are probably small or avian.
Life History and Behavior
Communication and Perception
Vocal communication is prevalent in all gibbon species. Mated pairs use duets to mark their territory and announce their presence to conspecifics. In addition to vocalizations, gibbons use facial expressions and body postures in communication. Tactile communication is of some importance between mates, as well as between parents and their offspring.
Communication Channels: visual ; tactile ; acoustic
Other Communication Modes: duets
Perception Channels: visual ; acoustic
Other species in this genus are reported to live as long as 44 years in captivity. Hylobates moloch is probably similar.
Status: captivity: 45 years.
Lifespan, longevity, and ageing
Gibbons are typically monogamous.
Mating System: monogamous
The available data on gibbons show no birth seasonality. A mated gibbon pair will produce an average of 5 to 6 offspring over their reproductive lifespan of about 10 to 20 years. Like most primates, H. moloch produces one young per litter, with a gestation length of around seven months. The interbirth period of a reproductive female is about 40 months.
Breeding interval: The interbirth period of a reproductive female is about 40 months.
Breeding season: There is no defined breeding season for H. moloch.
Average number of offspring: 1.
Average gestation period: 7 months.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); induced ovulation ; viviparous
Average gestation period: 243 days.
Average number of offspring: 1.
Although no specific information is available, most female gibbons nurse their offspring until the offspring are about two years old. Offspring leave their natal group when they become sexually mature.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents; extended period of juvenile learning
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2000Critically Endangered
- 1996Critically Endangered
- 1994Endangered(Groombridge 1994)
- 1990Endangered(IUCN 1990)
- 1988Endangered(IUCN Conservation Monitoring Centre 1988)
- 1986Endangered(IUCN Conservation Monitoring Centre 1986)
This species is endangered. The biggest threat to gibbons is deforestation of the tropical rainforests. Habitats are disappearing at an astonishing rate due to logging and agricultural demands. Without a sufficient range, gibbon species, along with other tropical species, are finding it much harder to exist. In an effort to help save these primates, reserves and parks are created, but there is no conservation program specifically for H. moloch. Other threats to gibbons include hunting for meat, and illegal poaching for the pet trade. These threats, although serious, are secondary to deforestation.
US Federal List: no special status
CITES: appendix i
IUCN Red List of Threatened Species: endangered
Median population density ranges are 2.7 groups/km2 or 9.0 individuals/km2 in lowland forest (<500 m), 2.6 groups/km2 or 8.6 individuals/km2 for hill forest (500-1,000 m), and 0.6 groups/km2 or 1.5 individuals/km2 for lower montane forest (1000-1,750 m) (Geissmann and Nijman 2006; Nijman 2004).
Three of the 15 locales that support the largest populations of silvery gibbons surveyed by Nijman are in national parks, while five are part of, or the entirety of, so-called âstrict nature reservesâ. The remaining seven locales are unprotected; approximately half of the remaining populations collectively reside here. In the interest of this species, it is these areas that require some level of increased protection (Nijman 2004). The second largest population of this species (for example in the Dieng Mountains) is not in a protected area.
In 2003, 56 Javan gibbons were maintained at eight Indonesian zoos, 15 at four Indonesian wildlife rescue centers, with five potential breeding pairs. There is no evidence that the species has bred successfully in captivity in Indonesia. Outside the range country, 48 Javan gibbons were maintained at ten institutions in nine countries, with six breeding pairs. The total ex-situ population is some 120 individuals, the majority of which are wild-caught (Nijman 2006).
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
These animals are not known to have a negative effect on humans.
Economic Importance for Humans: Positive
Hylobates moloch is not an important economic resource for humans. This species is not used for biomedical research, unlike some other primate species. Molochs are sometimes hunted for meat, and illegal poaching does occur for the pet trade.
Positive Impacts: pet trade ; food
The silvery gibbon (Hylobates moloch) is a primate in the gibbon family, Hylobatidae. Its coat is bluish-grey in colour, with a dark grey or black cap. Like all gibbons, silvery gibbons lack external tails, have dorsally placed scapulae, and reduced flexibility in their lumbar regions. They have long, curved fingers and very long forelimbs relative to their hind limbs. On average, they reach 8 kg in weight.
The silvery gibbon lives exclusively on the island of Java (Indonesia), where it inhabits deeply hidden portions of the rain forests. It is diurnal and arboreal, climbing trees skilfully and brachiating through the forests. Brachiation is aided by the possession of 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 births a single young, after a seven-month gestation. 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.
Threats and conservation
The silvery gibbon ranks among the most threatened primates. It is listed as Endangered on the 2009 IUCN Red List of Threatened Species, 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. 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. 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. Other large populations of several hundred are found in the Gunung Ciremai National Park and Gunung Gede Pangrango National Park. In the later there is a Javan Gibbon Centre that rehabilitates ex-captive gibbons.
Several zoos operate silvery gibbon breeding programs. Despite these efforts, the future survival of this species is in question.
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 males are usually very aggressive to others.
Some experts recognize two subspecies of Hylobates moloch:
- Western silvery gibbon or western Javan gibbon, H. m. moloch
- Eastern silvery gibbon or central Javan gibbon, H. m. pongoalsoni
These subspecies are not recognized by the IUCN Red List.
- 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.
- Andayani, N., Brockelman, W., Geissmann, T., Nijman, V. & Supriatna, J. (2008). Hylobates moloch. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- "The Silvery Gibbon Project". Retrieved 2007-12-11.
- Supriatna, Jatna: "Conservation Programs for the Endangered Javan Gibbon", in Primate Conservation, 2006 (21): 155–162
- The Silvery Gibbon Project: "Conservation Projects", retrieved 20 December 2013
- Geissmann, Thomas. "Gibbon Systematics and Species Identification". Retrieved 2006-04-13.
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