Gibbons are the animals we think of when we picture primates swinging gracefully through the rain forest.
These acrobatic mammals, endemic to the dense forests of southern Asia, are perfectly adapted to life in the trees and rarely descend to the ground. They have strong, hook-shaped hands for grasping branches, comically outsize arms for reaching faraway limbs, and long, powerful legs for propelling and gasping. Their shoulder joints are even specially adapted to allow greater range of motion when swinging.
Their dramatic form of locomotion, called brachiating, can move gibbons through the jungle at up to 35 miles (56 kilometers) an hour, bridging gaps as wide as 50 feet (15 meters) with a single swinging leap. Brachiating also gives gibbons the unique advantage of being able to swing out and grab fruits growing at the end of branches, which limits competition for their favorite foods.
When gibbons walk, whether along branches or in the rare instances when they descend to the ground, they often do so on two feet, throwing their arms above their head for balance. They are the most bipedal of all non-human primates and are often studied for clues to what evolutionary pressures may have led to human walking.
There are 15 recognized species of gibbons ranging from northeastern India to southern China to Borneo. They are all tailless, and their long coats vary from cream to brown to black. Many have white markings on their faces, hands, and feet. The largest species are known as siamangs, and can grow to 29 pounds (13 kilograms). Smaller species reach only about nine pounds (four kilograms).
Gibbons thrive on the abundant fruit trees in their tropical range, and are especially fond of figs. They will occasionally supplement their diet with leaves and insects.
Gibbons are monogamous (a rare trait among primates) and live in family groups consisting of an adult pair and their young offspring. The family will stake out a territory and defend it using loud, haunting calls that can echo for miles throughout the forest. Mated pairs, and even whole families, will sing long, complex songs together. Some species have even adapted large throat pouches to amplify their calls.
These iconic tree dwellers are among the most threatened primates on Earth. Their habitat is disappearing at a rapid rate, and they are often captured and sold as pets or killed for use in traditional medicines. All but one species of gibbon is listed as endangered or critically endangered.