Overview

Brief Summary

Biology

Gibbons are highly adapted for their arboreal lifestyle, feeding and sleeping in the trees; the long arms are used to throw themselves from tree to tree, easily covering gaps as wide as 10m (8). Males and females are monogamous, living in family groups with around 4 juvenile offspring who subsequently disperse (8). Group territories are actively defended by patrols, who engage in impressive bouts of loud calls and aggression (2).
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Description

The silvery or Javan gibbon has long fluffy silver-grey fur (2), with darker markings on the chest and cap (4). It has long arms and legs, long fingers and reduced thumbs, all of which are adaptations for brachiation (swinging through the trees from arm to arm) (2). Males produce simple 'hoot' calls, whilst the calls of females are more variable, ending in a 'bubble'. (4). Both sexes also give a 'scream' alarm call (8).
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Distribution

Range Description

Hylobates moloch is endemic to Java (Indonesia). It is mostly confined to Java’s western provinces (Banten and West Java), but is also present in central Java (as far east as the Dieng Mountains).
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Geographic Range

Molochs, Hylobates moloch, are endemic to the Indonesian island of Java.

Biogeographic Regions: oriental (Native )

Other Geographic Terms: island endemic

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Range

The silvery gibbon is endemic to the western half of the island of Java, Indonesia (3).
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Physical Description

Morphology

Physical Description

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

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Hylobates molochresides in floristically rich patches of relatively undisturbed lowland to lower montane rainforest mostly below 1,600 m, but sometimes up to 2,000–2,400 m (Nijman 2004). It can also tolerate moderately disturbed forest.

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)

Systems
  • Terrestrial
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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

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Inhabits tropical lowland, hill and montane (3) rainforests between sea level and 1500 meters (2). This species shows a preference for taller trees for resting, foraging and locomotion (3).
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Trophic Strategy

Food Habits

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 )

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Associations

Ecosystem Roles

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

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Predation

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.

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Life History and Behavior

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

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Life Expectancy

Lifespan/Longevity

Other species in this genus are reported to live as long as 44 years in captivity. Hylobates moloch is probably similar.

Average lifespan

Status: captivity:
45 years.

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Lifespan, longevity, and ageing

Maximum longevity: 45 years (captivity)
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Reproduction

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

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
C2a(i)

Version
3.1

Year Assessed
2008

Assessor/s
Andayani, N., Brockelman, W., Geissmann, T., Nijman, V. & Supriatna, J.

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

Contributor/s

Justification
Listed as Endangered because its population size is estimated to number fewer than 2,500 mature individuals, there is an observed continuing decline in the number of mature individuals, and no subpopulation contains more than 250 mature individuals. The change in status from Critically Endangered to Endangered reflects the availability of better information and does not suggest that the threats have decreased; in fact, threats continue to increase but do not yet reach the level necessary to be classified as Critically Endangered. There is concern about the legal status of the largest populations; this species, therefore, should be periodically reassessed so that current status and persistent threats are monitored.

History
  • 2000
    Critically Endangered
  • 1996
    Critically Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Endangered
    (IUCN Conservation Monitoring Centre 1986)
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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

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Status

Classified as Critically Endangered (CR) on the IUCN Red List 2006 (1), and listed on Appendix I of CITES (7).
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Population

Population
From 1994-2002, Nijman (2004) assessed the entirety of the silvery gibbon’s population in its known areas of occurrence by using fixed-point counts and forest transect walks, as well as by a review of literature. Their presence was detected by listening for gibbon song, and affirmed by local park officers and residents. He estimates that between 4,000–4,500 individuals remain in over 15 different locations. Over 95% of the gibbons are in populations of more than 100 individuals, and the four largest areas support populations of more than 500 individuals each (Nijman 2004). Asquith (2001) reported that in 1995 nine local populations had gone extinct, though Nijman found two of these locales to still harbor silvery gibbons. This is attributed to the effects of habitat disturbance and low population density on calling frequency, and suggests an under-representation of gibbon abundance and number of remaining populations (Nijman 2004). Small populations of the species are likely to go extinct; however, this will not impact the overall population estimate in the immediate future (Nijman pers. comm.).

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).

Population Trend
Decreasing
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Threats

Major Threats
The historical deforestation that affected Java in colonial times still maintains an overriding presence on the landscape, effectively restricting the arboreal silvery gibbon to continuous tracks of forest around mountain and volcano tops. However, habitat disturbance today is relatively slow, and populations of gibbons, while isolated, are substantial in size. Wildlife trade exerts an as yet un-quantified effect on Hylobates moloch (Nijman 2005). Populations seem to have become more or less stabilized in recent years as overall loss of habitat reached a climax some time ago. Though habitat loss continues, it is at a much slower rate today.
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The silvery gibbon has undergone a dramatic population decline principally as a result of habitat destruction (6), and also from the trapping of juveniles for the pet trade (2). The native forests of Java have been cleared for logging, agriculture and development, and the species has declined to fewer than 1000 individuals over then last 25 years (4). This gibbon appears to be on the very brink of extinction with only a handful of isolated viable populations remaining (6).
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Management

Conservation Actions

Conservation Actions
Javan gibbons have been protected throughout their range by Indonesian law since 1924, and are listed under CITES Appendix I.

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 “strict nature reserves”. 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).
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Conservation

In light of the critical status of this species in the wild, a Javan gibbon rescue and rehabilitation workshop was conducted in 1997 hosted by Conservation International and the University of Indonesia (2). It was agreed that a rescue and rehabilitation centre was needed and education programmes were proposed (5). Currently, the only viable protected population is found within the Gunung Halimun National Park; if this attractive primate is to survive it is vital that protection both within the park and in other areas is increased (6).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

These animals are not known to have a negative effect on humans.

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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

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Wikipedia

Silvery gibbon

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.[2]

Threats and conservation[edit]

The silvery gibbon ranks among the most threatened primates. It is listed as Endangered on the 2009 IUCN Red List of Threatened Species,[2] 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.[3] 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.[3] 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.[3] Other large populations of several hundred are found in the Gunung Ciremai National Park and Gunung Gede Pangrango National Park.[4] In the later there is a Javan Gibbon Centre that rehabilitates ex-captive gibbons.[5]

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.

Classification[edit]

Some experts recognize two subspecies of Hylobates moloch:[6]

  • 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.

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 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.
  3. ^ a b c "The Silvery Gibbon Project". Retrieved 2007-12-11. 
  4. ^ Supriatna, Jatna: "Conservation Programs for the Endangered Javan Gibbon", in Primate Conservation, 2006 (21): 155–162
  5. ^ The Silvery Gibbon Project: "Conservation Projects", retrieved 20 December 2013
  6. ^ Geissmann, Thomas. "Gibbon Systematics and Species Identification". Retrieved 2006-04-13. 
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