Nomascus gabriellae
red-cheeked gibbon
(Also: buff-cheeked gibbon)

Buff-cheeked gibbons are found in southeastern Asia, including southern Laos, eastern Cambodia, and central and southern Vietnam. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005; Max Planck Institute of Evolutionary Anthropology, 2005; Nowak, 1999)

Gibbons are all primarily arboreal species that generally avoid walking on the ground or swimming. The genus name, Hylobates, actually means "dweller in the trees." Hylobates gabriellae is found in tropical evergreen forests. These primates prefer lowland forests, and are rarely seen between above elevations of 1,500 to 2,000 m. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005; Nowak, 1999)

Gibbons have small body size compared to the other great apes in the family Hominidae. They range in weight between 7 and 11 kg and reach lengths between 60 and 80 cm. They have extremely long arms and relatively long legs. The hands are so long that they appear hook-shaped. The thumbs on the hands are not elongated and are not used for swinging from branch to branch; instead these thumbs are used more for grooming behavior. The body is generally held in an upright position.

In H. gabriellae, males have small, light-buff cheek patches that extend to the bottom of the eye and can be slightly separated at the neck. Females of this species are smaller than other gibbon females and have a black border on the ears. Females are generally brownish-yellow in color and can have a slight grayish tint to the darker hairs on the chest, on edges of fingers and toes, and on the outer forearm. Adult females may have slightly red-brown genital hairs, and usually there is a trace of a white fringe around the face. The pelage of buff-cheeked gibbons is very fine. Finally, females are only slightly smaller than males.

Pelage coloration changes as animals mature. The timing of the color changes is variable and it may take several months to complete. When a buff-cheeked crested gibbon is born, its coat is bright yellow. Within a few months, the color changes to black within a few months; only the cheek patches remain yellow. During this time, the young resemble adult males in their fur coloration. Males retain this color pattern as they mature, but females revert to a yellowish pelage around the time of sexual maturity. (Geissmann and The Gibbon Network, 2005; Max Planck Institute of Evolutionary Anthropology, 2005; Nowak, 1999)

The mating system of all gibbons is monogamy. All gibbon species have nuclear families consisting of a mated pair and 0 to 4 dependent offspring. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005)

The breeding pair in the nuclear family can produce an infant every 2 to 3 years. The interbirth interval tends to be long because females nurse the young for up to two years. There has never been any record of twins being born in a buff-cheeked gibbon family. Buff-cheeked gibbons have a relatively long gestation of 7 months, and the offspring stay with the family unit for 6 to 8 years. (Geissmann and The Gibbon Network, 2005)

Buff-cheeked gibbons have extensive parental investment by both parents. Females necessarily provide nutrition through nursing the young, but both parents may groom, carry, and protect the immature gibbons. The young stay with the parents for 6 to 8 years after birth. After this time, they move away to establish territories and families of their own. (Geissmann and The Gibbon Network, 2005)

Little research has been done on this species of gibbon in the wild, so its lifespan and survivorship in the wild are unknown. The only data on the lifespan of H. gabriellae is from captivity, where individuals of this species can live up to 50 years. (Gibbon Conservation Center, 2005)

Buff-cheeked gibbons are only social with their nuclear family. They are arboreal and diurnal. The most common form of communication is through visual displays and complex calls.

Gibbons are territorial. Both males and females perform vocal duets as part of maintaining their territory.

Gibbons are known as the best brachiators in the world. They swing below the branches suspended by their arms. Brachiation is an energetically advantageous mode of locomotion. It allows for relatively high speeds in the canopy and for jumps of 10 meters or more. When moving on branches or on the ground, gibbons walk on two legs (bipedalism), often using their arms for balance.

Buff-cheeked gibbons sleep sitting up, and the family sleeps together in prefered sleeping trees. The tight-knit family unit participates in social grooming, which is thought to reinforce the bonds between family members. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005; Nowak, 1999)

Gibbons are strongly territorial. Each family group occupies an area of about 20 to 50 hectares, but the typical territory size of this species has not been reliably determined in the wild. Territories are defended from intrusion by other gibbons by loud morning songs and by actively chasing intruders from the territory. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005)

Gibbons are famous for their calls. Gibbon groups produce loud, stereotyped songs in the early morning. Songs are thought to function primarily in defense of resources such as territories, food trees, and mates. However, songs may also help to attract potential mates. Gibbon songs include species-specific characteristics which are inherited rather than learned.

Mated pairs of buff-cheeked gibbons typically produce duet songs which consist of coordinated vocal interactions by both partners using sex-specific phrases. Other family members may participate in the song. Solo songs are typically produced by unmated buff-cheeked crested gibbons only.

Also, buff-cheeked gibbons have extended fields of skin glands situated in the axillary, sternal, and inguinal areas of the body. The glands produce a reddish secretion and are particularly active under hot temperatures and when the animals are excited. It is thought that the glands may play a role in olfactory communication. The glandular secretion also influences the amount of red visible in the yellowish female pelage coloration.

Tactile communication occurs when these animals groom one another, play, or mate. Visual communication signals, such as body postures and facial expressions, are also used by these primates. (Geissmann and The Gibbon Network, 2005; Gibbon Conservation Center, 2005; Max Planck Institute of Evolutionary Anthropology, 2005; Nowak, 1999)

This species is highly unstudied in the wild so all that is documented is from captive cases. Hylobates gabriellae is a selective eater and is mostly frugivorous. However, individuals have also been documented eating shoots, leaves, flowers, and occasionally insects. (Geissmann and The Gibbon Network, 2005; Max Planck Institute of Evolutionary Anthropology, 2005)

Adult gibbons typically live in the crown region of the forest where they have no natural predators except humans. In the lower stories of the forest, leopards, clouded leopards, and pythons may be potential predators. (Geissmann and The Gibbon Network, 2005)

Since all known behaviors and relationships are primarily studied in captivity, there is no documentation of the ecosystem role of H. gabriellae. However, the appetite of buff-cheeked gibbons for fleshy fruits would suggest they have a significant role in the disperal of seeds. (Geissmann and The Gibbon Network, 2005)

Some asian cultures use these animals for medicine, food, and pets, but not H. gabriellae exlusively. There is no particular eco-tourism draw with these animals. (Geissmann and The Gibbon Network, 2005; Nowak, 1999)

There is no known threat or negative impacts to humans by H. gabriellae.

The species is threatened by habitat loss (from development and logging) and by hunting. Also, extensive military activities have had a detrimental effect on the species mainly through habitat destruction. This species is not efficiently protected at present, not even in nature reserves and national parks. There are some local laws forbidding the hunt of these animals, but they are poorly enforced. Only international trade laws that forbid sale of these creature and their body parts in Europe and the US are enforced. ("Convention on International Trade in Endangered Species", 2004; Geissmann and The Gibbon Network, 2005; Nowak, 1999)

Traditionally, all crested gibbons were considered members of a single species (Hylobates concolor), and this species was considered the only representative of the subgenus Nomascus in the genus Hylobates. Buff-cheeked gibbons were considered a subspecies (H. concolor gabriellae) of that species. Recently, vocal characteristics and other features have suggested that buff-cheeked gibbons should be recognized as a distinct species and the genus Hylobates was split into several genera, including Nomascus. (Geissmann and The Gibbon Network, 2005)