Hylobates molochsilvery gibbon

Geographic Range

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


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.

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.

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    4 to 9 kg
    8.81 to 19.82 lb


Gibbons are typically 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
  • Average number of offspring
  • Average gestation period
    7 months
  • Average gestation period
    243 days

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


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


Gibbon groups are usually small, consisting of the mated pair, an infant and a juvenile, making the average group size about four individuals.

They are highly territorial and defend their territories by "singing." These loud calls can often be heard up to a kilometer away. Both male and female molochs call during territorial disputes. During these disputes, the female calls loudly, a "great call" and scream, while the male approaches the intruder and chases it away.

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.

  • Other Communication Modes
  • duets

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


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.

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

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.

Economic Importance for Humans: Negative

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

Conservation Status

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.


Nancy Shefferly (editor), Animal Diversity Web.

Jennifer Kuester (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.



uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate

  1. active during the day, 2. lasting for one day.

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


A substance that provides both nutrients and energy to a living thing.


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

island endemic

animals that live only on an island or set of islands.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


Having one mate at a time.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


found in the oriental region of the world. In other words, India and southeast Asia.

World Map

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year


5/1/94. "Gibbon Fact Sheet" (On-line). Accessed September 12, 1999 at http://aza.org/Programs/SSP/ssp.cfm?ssp=35&pub=79.

Cowlishaw, G. 1996. Sexual Selection and Information Content in Gibbon Song Bouts. Ethology, 102: 272-284.

Leighton, D. 1987. "Gibbons: Territoriality and Monogamy". Pp. 135-144 in B Smuts, D Cheney, R Seyfarth, R Wrangham, T Struhsaker, eds. Primate Societies. Chicago: University of Chicago Press.