The Gibbon

The genus, Hylobates, consists of nine to eleven species (depending on the classification) of lesser apes called gibbons. While there are definite morphological and behavioral differences between the species, the genus overall shows relatively little variance between its species (Leighton 1986). Thus, for this webpage I have chosen to group the species and discuss the most common characteristics of the genus Hylobates.

Photograph courtesy of David Pearce <http://www.primates.com/welcome.htm>

Gibbons are classified as lesser apes because their body weight and size are much smaller than gorillas, orangutans, and other Great Apes. Although they are small and have very long arms, gibbons differ from monkeys in that they lack a tail and have a different tooth arrangement (Singapore Zoological Gardens Docents 2004). Gibbons can weigh anywhere from 5 to 12 kilograms and can be 44 to 90 cm in length (Leighton 1986; Singapore Zoological Gardens Docents 2004). Depending on the species, gibbons can have a fur color of beige, black, brown, or gray, with various accent colors around the head. Other than slight size and color differences in certain species, gibbons exhibit very little sexual dimorphism. This lack of morphological differences between the sexes may be related to the equality exhibited between males and females both behaviorally and socially (Leighton 1986).

Gibbons are best known as the ‘singing ape.’ Their calls are often harmonious and pure in tone and can be heard from as far as 1 kilometer away (Raemaekers and Raemaekers 1985; Leighton 1986). Singing serves many roles for the gibbon, including territorial defense, maintenance of the pair bond, and general communication. They sing primarily in the morning hours and the songs can consist of male and/or female solos or pair duets (Raemaekers and Raemaekers 1985). Gibbons call most often from the boundaries of the territory (Islam and Feeroz 1992). Singing patterns differ between gibbon species and song characteristics have been found to be at least partially genetically determined (Geissman 1984). Calls of hybrid gibbons exhibit qualities of both the mother and father, showing that some recombination occurs that influences the gibbon’s call (Geissman 1984).

Photograph courtesy of S.P. Flannery <http://members.tripod.com/cacajao/index.html>

Gibbons give birth to a single offspring approximately every three years (Leighton 1986). Gibbon young are highly dependent on their mother for at least the first year, during which time the infant clings to the mother’s chest or stomach (Islam and Feeroz 1992). Since gibbons typically do not live more than 25 years in the wild and do not reach sexual maturity until they are 10, most gibbons give birth to only four or five offspring in their lifetime (Singapore Zoological Gardens Docents 2004). Every offspring, then, is critical to the gibbon’s lifetime reproductive success and much time and energy is spent in caring for the young.