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.
Known Predators:
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.
Average mass: 5.7 kg.
Range length: 440 to 635 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger
Average mass: 5900 g.
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.
Range lifespan
Status: wild: 25 (high) years.
Range lifespan
Status: captivity: 37 (high) years.
Kloss' gibbons can be found in the upper canopy of semi deciduous monsoon forests and tropical evergreen forests.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest
Kloss' gibbons, Hylobates klossi, are found in Siberut, Sipura, North Pagai, and South Pagai in the Mentawai Islands, western Sumatra, and Indonesia.
Biogeographic Regions: oriental (Native )
Hylobates means "dweller in the trees".
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.
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.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: duets ; choruses
Perception Channels: visual ; tactile ; acoustic ; chemical
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.
US Federal List: no special status
CITES: appendix i
IUCN Red List of Threatened Species: endangered
There are no known negative impacts of Kloss' gibbons.
Kloss' gibbons are a potential source of ecotourism dollars, as well as being important parts of a healthy ecosystem from which humans benefit.
Kloss' gibbons act as important seed dispersers in their forest ecosystems.
Ecosystem Impact: disperses seeds
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.
Animal Foods: birds; mammals; amphibians; reptiles; eggs; insects
Plant Foods: leaves; fruit; flowers
Primary Diet: herbivore (Frugivore )
Kloss' gibbons are monogamous. Mated pairs of males and females, with their young, form the basic social unit.
Mating System: monogamous
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.
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: 1.
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.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average number of offspring: 1.
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.
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
Kloss's gibbon (Hylobates klossii), also known as the Mentawai gibbon, the bilou or dwarf siamang, is an endangered primate in the gibbon family, Hylobatidae. It is identifiable in that it is all black,[4] resembling the siamang with its black fur, but is considerably smaller and lacks the siamang's distinctive throat pouch. Kloss's gibbon reaches a size 17 to 25 inches (44 to 63 cm) and weigh at most 13 pounds (6 kg). As is the case for all gibbons, they have long arms and no tail. Males and females are difficult to distinguish.[5]
Kloss's gibbon exclusively lives on the Mentawai Islands that lie to the west of Sumatra.[1] The Mentawai Islands consist four main islands that are part of an island archipelago.[6] These islands are hearths of biodiversity, and are the homes of many endemic species.[6] It is a diurnal inhabitant of the rain forest that hangs in the trees from its long arms and rarely comes to the ground. Because Kloss's gibbon rarely comes out of the canopy, these gibbons use tree limbs to cross obstacles like bodies of water.[7] Like all species of gibbons it lives together in pairs that stake out a territory from approximately 49 to 74 acres (20 to 30 hectares) of size. This area is defended vehemently against other gibbons. Its diet consists mainly of fruits, occasionally also eating different plant parts, bird eggs, insects and small vertebrates.
Kloss's gibbon are unique gibbons because the two sexes do not vocalize songs in unison.[8] Male Kloss's gibbon sing before the sun rises and female Kloss's gibbon vocalize songs once the sun has risen.[8] Female Kloss's gibbon calls are unique and have slight variations in the different stages of the call.[9] The calls emitted by the females could offer other members of the species information about their position in the canopy.[9]
The reproductive cycle of Kloss's gibbon is similar to that of other gibbons. Every two to three years the female may give birth to a single young (with a gestation period of seven months). The young is weaned in the middle of its second year, and is fully mature in about seven years. Their life expectancy is about 25 years in the wild, and up to 40 years in captivity. Kloss's gibbons are monogamous, and male Kloss's gibbons use territory to attract and court possible mates.[10] Territories are often contested and Kloss's gibbons defend their territories with aggression and threats.[10] During courtship, males and females defend territory together, and mating only occurs after the females deems the male capable of defending a suitable territory.[10]
Kloss's gibbon are picky eaters, and never consume over-ripened fruit.[5] Kloss's gibbons diet consists of fruit, leaves, shoots, and insects.[5] Kloss's gibbons favorite fruit is figs, but these gibbons do not spend a lot of time eating figs because figs are scarce on the Mentawai Islands.[5]
When Kloss's gibbons are observed by human researchers, they adapt and become less afraid, a process called habituation. Kloss's gibbons can become habituated to humans and will not flee when they are observed.[11] Unhabituated Kloss's gibbons sometimes exhibit a warning behavior in which they act as a lure toward people.[11] One male gibbon will produce warning calls and attract attention to himself while other members of his group make their escape.[11] Kloss's gibbons behavior help it stay cryptic, possibly to help them avoid hunting pressure.[11] Female Kloss's gibbons sing less frequently than males, and males only sing in the predawn when visibility isn't optimal for hunting.[11] Kloss's gibbons also exhibit less aggregate behavior like grooming and playing, possibly to reduce their visibility and stay hidden from hunters.[11]
Kloss's gibbon is in jeopardy of going extinct.[8] Kloss's gibbon is classified as endangered by the IUCN (2021).[2] Recent estimates conclude that there are around 20,000 to 25,000 Kloss's gibbons alive in the wild, and its numbers are declining.[12] Over the last two and a half decades, the population size of Kloss's gibbon has fallen by 50%.[12] There are several threats that pose significant risk to Kloss's gibbon. Kloss's gibbon has no natural predators, and humans are the main threat to the existence of this primate.[7] Native peoples of the Mentawai Islands kill Kloss's gibbon and other endemic primates for subsistence, and also participate in poaching activities.[6] Globalization and industrialization in the Mentawai Islands are contributing toward the degradation of high quality habitat needed by Kloss's gibbon.[13] Road development and the adoption of air rifles are allowing natives to kill Kloss's gibbon easier and at higher rates.[13] Kloss's gibbon spends the majority of its time in the tree canopy, and as a result, this species requires undisturbed, old-growth forest habitats to sustain itself.[6] Kloss's gibbon is at risk due to habitat loss, as its homeland islands are suffering from deforestation.[6] Conservationists focused on improving Kloss's gibbons endangered status need to protect and preserve the high quality habitat needed by these gibbons.[6] Fragments of habitat need to be connected to allow movement without risk of exposure in highly modified areas.[6] Local government has been cooperating with global organizations such as UNESCO to raise awareness as well as increase the amount of protected land in the Mentawai Islands.[13]
Kloss's gibbon (Hylobates klossii), also known as the Mentawai gibbon, the bilou or dwarf siamang, is an endangered primate in the gibbon family, Hylobatidae. It is identifiable in that it is all black, resembling the siamang with its black fur, but is considerably smaller and lacks the siamang's distinctive throat pouch. Kloss's gibbon reaches a size 17 to 25 inches (44 to 63 cm) and weigh at most 13 pounds (6 kg). As is the case for all gibbons, they have long arms and no tail. Males and females are difficult to distinguish.