Silvery Gibbon Hylobates moloch
Silvery Gibbon Hylobates moloch
Red List Status: Endangered
Locations: Indonesia (island of Java, including provinces of Banten, West Java, and Central Java as far east as the Dieng Mountains)
The Silvery #Gibbon 🩶🐒🐵 of genus ‘Hylobates’ meaning ‘Forest Walker’. They sing to each other in ‘local’ accents and do thrilling acrobatics 🤸♂️ They are #endangered, help them to survive! #BoycottPalmOil #Boycott4Wildlife 🌴🔥⛔️ @palmoildetect https://palmoildetectives.com/2021/02/06/silvery-gibbon-hylobates-moloch/
Share to BlueSky Share to Twitter The Silvery Gibbon belongs to the genus Hylobates. The word Hylobates means ‘Forest Walker’ in Greek. The gibbons in this genus are known for the white circle of fur around their faces. They are known to communicate in species-specific song when defining territory or attracting mates. They sing in regional accents to each other, have long swinging arms, inquisitive natures and superior acrobatic skills, they spend most of their lives high up in the tree-tops.
Appearance & Behaviour
Silvery gibbons are small apes, their bodies draped in long, silvery-grey fur with a dark grey or black cap on their heads and a distinctive fringe of white or light grey around their dark faces. Adults typically weigh around 6 kilograms, with males and females similar in size. Their arms are exceptionally long, spanning twice their body length, allowing them to brachiate—swing hand over hand—through the treetops with remarkable speed and agility. Unlike many other gibbon species, silvery gibbons do not sing duets; instead, it is the females who dominate the morning chorus with loud, haunting calls that echo through the forest. These family groups, usually consisting of a monogamous pair and their offspring, move together through the canopy, their movements fluid and almost effortless.
Threats
Palm oil and agricultural deforestation
Silvery gibbons face severe pressure from the ongoing loss of their forest habitat. In Java, particularly in Banten Province, deforestation is accelerating at a high rate. The conversion of forests to agricultural land, including palm oil plantations and other crops, leaves behind only isolated fragments of habitat. This fragmentation forces gibbons into ever-smaller territories, increasing stress and competition for resources. The once-continuous canopy that silvery gibbons depend on is being replaced by agricultural fields, making survival increasingly difficult for these arboreal primates.
Illegal pet trade, illegal poaching and hunting
Silvery gibbons are targeted by hunters for both meat and the illegal pet trade. Poachers often kill adult gibbons to capture infants, who are then sold as pets in markets throughout Indonesia. This practice not only removes individuals from the wild but also disrupts family groups and weakens the social structure essential for gibbon survival. The illegal pet trade remains a persistent and devastating threat, driven by demand for exotic animals and compounded by the ongoing destruction of their natural habitat.
Timber logging and habitat fragmentation
Logging operations further degrade and fragment the remaining forest habitat of silvery gibbons. Roads and clearings cut through the forest, severing the vital canopy connections that gibbons rely on for movement and social interaction. Fragmentation isolates populations, reducing genetic diversity and making them more vulnerable to disease and environmental change. In many areas, only small, isolated groups of gibbons remain, cut off from neighbouring populations by cleared land.
Climate change
Shifting rainfall patterns and rising temperatures threaten to alter the delicate balance of Indonesia’s forests. Changes in fruiting and flowering times can disrupt the silvery gibbon’s food supply, while extreme weather events destroy habitat and isolate populations even further. The silvery gibbon’s world is becoming hotter, drier, and less predictable, with the forests they depend on shrinking year by year.
Diet
Silvery gibbons are primarily frugivorous, with fruit making up about 61% of their diet and leaves accounting for another 38%. They also consume flowers and, to a lesser extent, insects. The silvery gibbon’s foraging is a daily journey through the treetops, as they search for scattered fruit-bearing trees. Their home ranges average between 17 and 60 hectares, and several families may share overlapping territories, especially where fruit is abundant. The rhythm of their feeding is woven into the life of the forest, as they play a vital role in seed dispersal and the regeneration of their ecosystem.
Mating & Reproduction
The Silvery Gibbon is considered Endangered based on a suspected population reduction of 50% or more over the course of three generations (2001-2015, 2016-2030, 2031-2045). This ongoing decline is due to the combined threats of forest habitat loss and hunting for subsistence purposes, in addition to supplying the pet trade.
IUCN Red List
Silvery gibbons are monogamous, forming lifelong pair bonds. There is no set breeding season, and females give birth to a single infant after a gestation period of about seven to eight months. The mother carries her baby close for the first year, nursing and protecting it as the family group moves through the forest. Weaning occurs at around 18 months, and offspring remain with their parents until they reach maturity at about eight years of age, when they leave to form their own families. The family unit is tight-knit, with both parents sharing in the care of their young and strong emotional bonds that are essential for survival in a changing world.
Geographic Range
Silvery gibbons are endemic to the island of Java, Indonesia, with their range primarily in the (still forested) western regions of Banten and West Java, and extending into parts of Central Java as far east as the Dieng Mountains. They inhabit lowland and lower montane rainforests up to 2,400 metres above sea level, though they are most commonly found below 1,600 metres. Their historical range has contracted dramatically due to deforestation and human infrastructure development, and they are now restricted to fragmented forest patches. The sounds of the silvery gibbon—once a common feature of Java’s forests—are now tragically heard in very few places.
FAQs
How many silvery gibbons are left?
Estimates suggest that fewer than 2,500 mature silvery gibbons remain in the wild, with populations continuing to decline due to habitat loss, fragmentation, and the illegal pet trade. In some areas, fewer than 2,000 individuals are considered genetically viable for the continuation of the species. The silvery gibbon’s future is precarious, and urgent action is needed to prevent their extinction.
What are the characteristics of the silvery gibbon?
Silvery gibbons are small, slender apes with long, silvery-grey fur and a dark cap on their heads. They lack a tail, and their arms are exceptionally long—up to twice their body length—allowing them to brachiate through the forest canopy with remarkable speed and grace. Adults typically weigh between 6 and 8 kilograms, with males slightly larger than females. Silvery gibbons are strictly arboreal, rarely descending to the forest floor, and live in small, monogamous family groups. The female leads the morning chorus with haunting, resonant calls that can be heard for up to a kilometre.
Is a silvery gibbon a monkey?
A silvery gibbon is not a monkey, but a lesser ape. The primary difference between a lesser ape (like a gibbon) and a monkey is that apes, including lesser apes, do not have tails, while most monkeys do. Additionally, apes are generally larger and have broader chests, while monkeys tend to be smaller and have narrower chests. Apes also have shoulder joints that allow for brachiation—swinging through trees—and some species exhibit higher intelligence and tool use. Lesser apes, such as gibbons and siamangs, are smaller than the great apes (chimpanzees, gorillas, orangutans, and humans) but share these key anatomical and behavioural traits. In contrast, most monkeys have tails, which they use for balance, and are more adapted to running along branches rather than swinging through the trees. While monkeys are intelligent, apes generally exhibit more complex cognitive abilities and social behaviours.
Why will the silvery gibbon become extinct in the next decade?
The silvery gibbon faces multiple, compounding threats that make extinction within the next decade a real possibility. Habitat loss due to deforestation has reduced their forest home to less than 4% of its original extent. Fragmentation isolates populations, making them more vulnerable to disease and genetic decline. The illegal pet trade continues to remove individuals from the wild, and climate change is altering the availability of food and water. Without urgent, large-scale intervention, the silvery gibbon is likely to disappear from much of its remaining range.
Are gibbon monkeys aggressive?
Gibbons, including silvery gibbons, are not monkeys but lesser apes. In their natural environment, silvery gibbons are highly territorial and will defend their home range with vocalisations and, if necessary, physical displays. Males and females both play a role in defending their territory, with the female’s morning calls and the male’s aggressive responses to intruders. Within the family group, silvery gibbons are generally peaceful and nurturing, with strong social bonds between parents and offspring. In captivity, gibbons can show aggression during introductions or when resources are contested, but this is not typical of their behaviour in the wild.
Are silvery gibbons Endangered?
Yes, the silvery gibbon is classified as Endangered on the Red List of Threatened Species. Their population is estimated at fewer than 2,500 mature individuals and is declining due to habitat loss, fragmentation, and the illegal pet trade. The silvery gibbon’s survival is at risk, and their future depends on the protection of remaining forest habitat and the reduction of human-induced threats
Take Action!
Use your wallet as a weapon and #BoycottPalmOil #Boycott4Wildlife. Support indigenous-led conservation and agroecology. Reject products linked to deforestation, mining, and the illegal wildlife trade. Adopt a #vegan lifestyle and #BoycottMeat to protect wild and farmed animals alike. Every choice matters—stand with the silvery gibbon.
Further Information
Kim, S., Lappan, S., & Choe, J. C. (2010). Diet and ranging behavior of the endangered Javan gibbon (Hylobates moloch) in a submontane tropical rainforest. American Journal of Primatology, 72(10), 991–1000. https://doi.org/10.1002/ajp.20893
Nijman, V. 2020. Hylobates moloch. The IUCN Red List of Threatened Species 2020: e.T10550A17966495. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T10550A17966495.en. Downloaded on 06 February 2021.
Reyes, K. R., Patel, U. A., Nunn, C. L., & Samson, D. R. (2021). Gibbon sleep quantified: The influence of lunar phase and meteorological variables on activity in Hylobates moloch and Hylobates pileatus. Primates, 62, 749–759. https://pubmed.ncbi.nlm.nih.gov/34052907/
Silvery Gibbon Hylobates moloch
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