Gibbons: Vocal and Endangered Animals of the Rainforest
Gibbons are slender, long-limbed apes that live in tropical and subtropical forests in Southeast Asia. The animals are best known for their loud, penetrating calls and their ability to swing athletically from one tree branch to another. Gibbons are intelligent and social animals. They belong to the order Primates, just as we do.
There are four genera of gibbons and about eighteen species. Scientists disagree about the actual number of species that exist. Unfortunately, most gibbons are endangered. Deforestation is destroying their habitat in many areas. In addition, females are shot so that their babies can be captured and sold as pets. Another problem is that poachers kill the animals to obtain body parts used in traditional medicine.
The scientific name of an organism consists of the genus followed by the species. The lar or white-handed gibbon is named Hylobates lar. Its genus is Hylobates and its species is lar. "Genera" is the plural form of "genus".
Gibbons are sometimes referred to as lesser apes, while bonobos, chimpanzees, orangutans, and gorillas are classified as great apes. The term “lesser” refers to the slender, lightweight bodies of gibbons compared to the denser and bulkier bodies of the great apes.
Gibbons have small heads and flat faces. The face is hairless, to a greater or lesser extent. The animals have longer arms than legs. Their hands have four long fingers and an opposable thumb, like ours. Their feet have five toes. Unlike our feet, however, a gibbon's feet are flexible and have an opposable big toe. These features enable the animal to grip tree branches with its feet. The palms and bottoms of the feet are hairless. Like other apes, gibbons have no tail.
Gibbons have dense hair, which ranges from very pale brown to black in colour. There may be white areas on the body as well. Some gibbons have a white ring around their face.
Gibbons, great apes, and humans belong to the order Primates and the superfamily Hominoidea. Gibbons belong to the family Hylobatidae. The great apes and humans belong to the family Hominidae.
Gibbons are arboreal animals and are active during the day. They travel through their forest habitat by swinging from branch to branch at high speed, alternating the hand that is used to attach them to a tree. They curl their fingers around a branch like a hook as they travel. This method of locomotion is known as brachiation. Gibbons also walk along tree limbs and leap from branch to branch.
The animals are such adept acrobats that they may reach a speed of up to thirty-five miles an hour as they brachiate through the trees. In addition, they can travel over a gap of up to fifty feet.
Wild gibbons rarely come to ground, but when they do they walk bipedally (on two legs). They often raise their arms out to their sides and above their heads to help them balance as they walk on the ground or in trees.
Social Behaviour and Vocalizations
Gibbons are social animals. They live in families made of a male, a female, and several young offspring. Their day begins with a period of loud vocalizations. The sounds are often known as songs and are sometimes quite musical. Males and females may sing duets. Other members of the family sometimes join in, too. Vocalizations occur at other times of the day as well and may consist of calls, hoots, shrieks, whoops, and barks.
Gibbons produce sounds to maintain bonds within their social group, to advertise or defend their territory, and to attract mates. Unfortunately, their vocalizations betray their location to human hunters.
When they are not foraging for food, gibbons often spend their time grooming each other. This action helps to strengthen the bonds between individuals.
Unlike the great apes, gibbons don’t make sleeping nests. In the evening they find a good place to sit in their regular sleeping tree, such as a fork in the branches, and then settle down for the night. The rear end of a gibbon is covered by a pad of callus called an ischial callosity, which very likely makes sitting on the branches more comfortable than it would otherwise be.
Gibbons are omnivorous. The largest component of their diet is fruits, especially sugary fruits like figs. They eat other plant parts as well, including leaves, stems, buds, and flowers. They also eat animals, such as insects, spiders, and bird eggs. Some gibbons eat small birds. Gibbons drink by dipping their hands into water or rubbing them over wet leaves and then licking their fur. They also lick their fur after rain.
Reproduction and Lifespan
Male and female gibbons generally pair for life. The gestation period is about seven to seven and a half months, depending on the species. There is usually only one baby, although occasionally twins are born.
The baby is weaned between one and two years of age. It stays with its mother for about six years. Around this time the gibbon becomes sexually mature and leaves the group to find a partner and start its own family.
In the wild, the maximum lifespan of gibbons seems to be twenty-five to thirty years, but the animals have lived for forty years in captivity.
The four genera of gibbons are Nomascus (seven species), Symphalangus (one species), Hoolock (three species) and Hylobates (seven species).
The Siamang: An Unusual Gibbon
The siamang (Symphalangus syndactylus) is black in colour. It's the only species in its genus. It's notable because it's bigger than other gibbons and has a very loud voice. The animal has a large throat pouch that expands when it vocalizes and amplifies the sound that it makes. Another interesting feature of the siamang is that its opposable big toe is widely separated from its other toes. This enables the animal to carry objects in both its hands and its feet.
The siamang lives in Sumatra and on the Malay peninsula. Like other gibbons, it's a social animal that lives in the tree canopy and has an omnivorous diet. The individuals in a group stay close together during the day and search for food as a group. Siamangs generally move more slowly than other gibbons, but they are still very agile animals. They are strongly territorial. Like most gibbons, the siamang is endangered in the wild.
The video below includes the impressive calls of siamangs at the Cincinnati Zoo.
The Sad Plight of the Hainan Gibbon
The Hainan gibbon or Hainan black-crested gibbon of China (Nomascus hainanus) is critically endangered and is the rarest primate in the world. Only around 25 animals exist. They live in a small area of Hainan Island in a single population consisting of four groups. Their numbers have been decimated by deforestation.
Scientists at the Zoological Society of London have discovered that the gibbons were once common and could be found in half of China (according to the reports that the researchers studied). The animal's numbers began to dwindle as the human population grew. In the 1950s, about 2000 Hainan gibbons existed. Today the species is in serious danger of extinction.
The gibbon population has increased slightly since the 2003 count of 13 individuals, which is good news. The surviving animals live in a nature reserve, which is also good news. However, the laws that have been passed to protect the animals are not always followed. In addition, the population is so low that an epidemic of disease or a natural disaster could wipe the species out. Another problem is that there is little genetic diversity in the population. It's impossible for a gibbon in the population to mate with anyone other than a relative.
The Hainan gibbon is said to be sexually dichromatic because the male and the female have a different colour. The male is black and the female has a tan colour.
Hoolock gibbons are the only apes in India. They are also found in China and Myanmar. They are the largest gibbon after the siamang. Like the Hainan gibbon, hoolock gibbons are sexually dichromatic. The female is a buff or tan colour and the male is black.
Until an announcement in January 2017, there were considered to be two species of the gibbon—the western hoolock, or Hoolock hoolock, and the eastern hoolock, or Hoolock leuconedys. Scientists now say that a third species exists in part of China and Myanmar. The animals have been observed for some time, but researchers finally agree that they are sufficiently different from other hoolock gibbons to be classified differently. The scientific name of the newly classified animal is Hoolock tianxing. Its common name is the Skywalker hoolock gibbon.
The IUCN (Internation Union for Conservation of Nature) has classified the population of the western hoolock as endangered and that of the eastern hoolock as vulnerable. The population of the Skywalker hoolock gibbon is unknown, but it's believed to be very low. About 200 animals are thought to exist in China as well as an unknown number in Myanmar. The species is probably endangered.
It has been named the Skywalker hoolock gibbon - partly because the Chinese characters of its scientific name mean "Heaven's movement" but also because the scientists are fans of Star Wars.— Rebecca Morelle, BBC
While deforestation is having the most serious effect on the Hainan gibbon, other gibbons are bring affected by the same process. The animals are so dependent on trees for their way of life that the loss of forest is devastating. As is true in so many parts of the world, humans are clearing land of its original vegetation and using it for their own purposes. The establishment of gibbon sanctuaries in the wild is very important. It's also important to protect the animals from hunters in these sanctuaries. A sanctuary in name only isn't much good.
Rescue and rehabilitation centres have been established to protect endangered gibbon populations and to promote their conservation. These organizations are badly needed. The centres also serve to educate the public about the plight of the world's gibbons.
When considering a gift of money to an organization that helps animals, a potential donor should investigate the reputation of the organization, the percentage of each donation that is used to help animals, and the way in which the organization uses the donated money.
Some conservation agencies have websites that allow people to help gibbons even if they live nowhere near Asia. The organizations accept donations and contribute money from online stores to the conservation effort. They may also enable visitors to "adopt" a gibbon at a rescue centre. This means that a person will get periodic news about "their" gibbon in return for a stipulated donation.
All types of help can be valuable in the effort to protect gibbons. They certainly need our aid. It would be horrible to lose these wonderful animals from the planet.
- Gibbon basics from the Gibbon Conservation Center
- Siamang facts from the Smithsonian's National Zoo and Conservation Biology Institute
- Nomascus hainanus entry from the International Union for Conservation of Nature
- "Only 25 Hainan gibbons remain - what next for the world's rarest primate?" from The Conversation
- "Hainan gibbon decline charted in Chinese records" from the BBC
- Hoolock gibbon facts from the National Primate Research Center, University of Wisconsin - Madison
- " 'Star Wars' gibbon is new primate species" from the BBC
© 2010 Linda Crampton