Hylobates klossiiKloss's gibbon

Geographic Range

Kloss' gibbons, Hylobates klossi, are found in Siberut, Sipura, North Pagai, and South Pagai in the Mentawai Islands, western Sumatra, and Indonesia. (Haimoff and Tilson, 1985; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)


Kloss' gibbons can be found in the upper canopy of semi deciduous monsoon forests and tropical evergreen forests. (Haimoff and Tilson, 1985; "Kloss' gibbon (Hylobates klossii)", 2002)

Physical Description

Hylobates klossii has long forearms for brachiation. These tail-less, slender primates have dense, glossy, black hair with buttock pads and a large throat sac located under the chin. The throat sac helps to enhance their calls. Females are slightly larger than males, with males weighing about 5.6 kg and females weighing about 5.9 kg. Head and body length ranges from 440 mm to 635 mm. (Chivers and MacDonald, 2001; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

  • Sexual Dimorphism
  • female larger
  • Average mass
    5.7 kg
    12.56 lb
  • Average mass
    5900 g
    207.93 oz
  • Range length
    440 to 635 mm
    17.32 to 25.00 in


Kloss' gibbons are monogamous. Mated pairs of males and females, with their young, form the basic social unit. (Haimoff and Tilson, 1985; "Kloss' gibbon (Hylobates klossii)", 2002)

The gestation period of H. klossii lasts 7 to 8 months, with one infant born every 2 to 3 years. Weaning occurs early in the second year of life. Kloss' gibbons reach sexual maturity at 6 to 7 years of age. Young do not usually disperse from their family unit until they reach late adolescence. The testicular sac in males is covered by short, sparse hairs. In females, the labia majora is prominent, making it difficult to distinguish males from females in the field. (Chivers and MacDonald, 2001; Parker, 1990; Whitten, 1982)

  • Breeding interval
    One infant is born every 2 to 3 years to an individual female.
  • Breeding season
    These animals breed throughout the year.
  • Average number of offspring
  • Average number of offspring
  • Range gestation period
    7 to 8 months
  • Range weaning age
    24 (high) months
  • Range age at sexual or reproductive maturity (female)
    6 to 7 years
  • Range age at sexual or reproductive maturity (male)
    6 to 7 years

Males and females participate in caring for the young. Around the time of adolescence, males and females will disperse from their parent's group. Often parents will assist dispersing adolescents in obtaining territory by accompanying the young into new territory and threatening those occupying the new area. (Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • male
      • female
  • post-independence association with parents
  • extended period of juvenile learning


The lifespan of Kloss' gibbons may be as long as 25 years. Other members of the genus Hylobates are known to live upwards of 44 years in captivity. (Parker, 1990)

  • Range lifespan
    Status: wild
    25 (high) years
  • Range lifespan
    Status: captivity
    37 (high) years


Hylobates klossii is an arboreal species that moves from tree to tree by brachiation. Often these trees are at least 10 meters apart. This causes them to have moments where they are moving through the air not supported by any trees, almost as if they are flying. If on the ground, they can move bipedally for very short distances. They move an average of 1,514 meters per day and are diurnal, sleeping in trees at night. They often they use the same trees each night for sleeping. They are active up to 10 hours per day.

Kloss' gibbons are territorial, with adolescents and sub-adult males cooperating with their father to protect the group's territory. (Chivers and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

  • Average territory size
    .200 - .350 km^2

Home Range

Mated pairs occupy a small home range of about 20 to 35 hectares, of which they defend about 10 hectares from up to 6 other groups that occupy the surrounding square kilometer. (Chivers and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

Communication and Perception

Kloss' gibbons are known for their magnificent vocal communication. Females tend to have the most distinctive calls with a slow rise and fall, interrupted by a trill sequence. Male calls consist of moans and "quiver-hoots". Males will sing solos from 10 minutes up to 2 hours in both the pre- and post-dawn hours. Often, breeding pairs form duets together 2 to 3 hours after dawn, with the female's contribution lasting about 15 minutes. Occasionally, the young will join in the duet of their parents. It has been hypothesized that the duets are a means of intimidating neighbors to defend their territory and/or as a way to maintain social organization. Studies have shown that both males and females can be identified by the individuality of their calls, with each animal having its own unique voice. (Cowlishaw and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999)

Kloss' gibbons also use chemical, tactile, and visual modes of communication. Social grooming is an important form of social bonding and facial and body gestures are important ways of communicating among gibbons. Another important interaction is play behavior centered on the infant. ("Kloss' gibbon (Hylobates klossii)", 2002)

Food Habits

Kloss' gibbons are primarily frugivorous, preferring to eat fruits with high sugar content, such as figs, 72 percent of the time. They will also consume flowers, eggs, small vertebrates, and insects 25 percent of the time. This species tends to spend time apart from members of its own group while feeding -- up to 50 meters at times. In the wild, Kloss' gibbons have been observed to spend a large amount of feeding time searching for arthropods. (Massicot, 2002; Nowak, 1999; Whitten, 1982; "Kloss' gibbon (Hylobates klossii)", 2002)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs
  • insects
  • Plant Foods
  • leaves
  • fruit
  • flowers


Predators of Kloss' gibbons include leopards, snakes, and large birds of prey. Their social system means that many individuals are vigilant and will warn other members of the troup of impending danger. (Massicot, 2002; Nowak, 1999; Whitten, 1982)

Ecosystem Roles

Kloss' gibbons act as important seed dispersers in their forest ecosystems.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Kloss' gibbons are a potential source of ecotourism dollars, as well as being important parts of a healthy ecosystem from which humans benefit.

Economic Importance for Humans: Negative

There are no known negative impacts of Kloss' gibbons.

Conservation Status

The IUCN lists H. klossii as vulnerable due to the extent of occurrence and/or quality of habitat. The status of H. klossii is threatened because of an increased human population, hunting, and deforestation. CITES lists H. klossii on their Appendix I list. ("IUCN Red List of Threatened Species", 2002; "The CITES Appendices I, II, and III", 2002; Massicot, 2002; Nowak, 1999)

Other Comments

Hylobates means "dweller in the trees". (Nowak, 1999)


Nancy Shefferly (editor), Animal Diversity Web.

Alix Marcoux (author), Michigan State University, Barbara Lundrigan (editor), Michigan State University.



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


to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

  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.


union of egg and spermatozoan


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.


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


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.


remains in the same area


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


2002. "IUCN Red List of Threatened Species" (On-line ). IUCN 2002. Accessed 03/04/03 at http://www.redlist.org/search/details.php?species=10547.

Wisconsin Primate Research Center. 2002. "Kloss' gibbon (Hylobates klossii)" (On-line). Primate Info Network. Accessed March 05, 2003 at http://pin.primate.wisc.edu/factsheets/hylobates_klossii.html.

Convention on International Trade in Endangered Species of Wild Fauna and Flora. 2002. "The CITES Appendices I, II, and III" (On-line ). CITES. Accessed 03/04/03 at http://www.cites.org/eng/append/index.shtml.

Chivers, D., D. MacDonald. 2001. Gibbons. Pp. 398-403 in The Encyclopedia of Mammals, Vol. 2. New York: Facts on File, Inc..

Cowlishaw, G., D. MacDonald. 2001. Defense by Singing: Great calls and Song Bouts of the Gibbons. Pp. 404-405 in The Encyclopedia of Mammals, Vol. 2. New York: Facts on File, Inc..

Haimoff, E., R. Tilson. 1985. Individuality in the female songs of wild Kloss' gibbons (<<Hylobates klossii>>) on Siberut Island, Indonesia. Folia Primatologica, 44: 129-137.

Massicot, P. 2002. "Animal Info - Kloss's Gibbon" (On-line ). Animal Info Organization. Accessed 03/05/03 at http://www.animalinfo.org/species/primate/hyloklos.htm.

Nowak, R. 1999. Walker’s Mammals of the World. Baltimore: The Johns Hopkins University Press.

Parker, S. 1990. Old World Primates. Pp. 350-355 in Grzimek’s Encyclopedia of Mammals, Vol. 2. New York: McGraw-Hill Publishing Company.

Whitten, A. 1982. Diet and feeding behavior of Kloss gibbons on Siberut Island, Indonesia. Folia Primatologica, 37: 177-208.