This week, Animals Anonymous will centre on once more a whole family of species; the Gibbons. This is a more extensive famiily than some might suppose, and this month, another addition was made. Under the four genus of Gibbon, seventeen species are recognized - including the newest - with some branches which split into even more
As Gibbons are an extensive family, making correlations which are valid for the whole family is difficult, but not impossible. As a family, they are considered as "smaller" or "lesser apes", as they differ too much from great apes to be classified in the same family. They do share some traits in their genetics and having no tail, but their behaviour and appearance differs greatly.
Gibbons can be found across most of Southeast Asia, also inhabiting some of the islands on the region. They make thei habitat mostly in trees, though they are known to walk the forest floor from time-to-time, doing so with their arms over their head, walking on two feet. This can look odd as their arms are the longest of all primates, compared to their body size. This is necessary to accomodate swinging
through the tree-tops, but may look awkward when folded in. Diet-wise, Gibbons rely mainly on fruit, flowers and leaves, though they will supplement this occasionally with insects.
Gibbons enjoy a trait which is rare in land mammals, namely singing. Early in the morning, Gibbons produce beatiful songs which can be heard as far as 1 to 2 kilometers away. These songs may last between ten to thirty minutes and can be used to identify individuals as well as gender and species of the singer. When Gibbons are mated, they will duet together which strengthens their bond. It is believed Gibbons are monogamous and bond for longer duration. The social structure in which Gibbons live therefore often consists of a mated pair of Gibbons and their juvenile offspring.
Gibbons can be distinguished in Crested Gibbons, Dwarf Gibbons, Hoolock Gibbons and the Siamang.
is the largest of the Gibbons and can measure up to two times the size of other Gibbons. Their fur consists of black, adults sporting a grey area around their chin and mouth. Though there is sexual dimorphism among some Gibbons, male and female Siamangs look alike. Their throat sac, present in both males and females, can be highly visile due to the lighter colour around their throat.
When talking about Dwarf Gibbons
, we consider the the Lar Gibbon, Bornean White-Bearded Gibbon, Agile Gibbon, Müller's Bornean Gibbon, Silvery (Javan) Gibbon, Pileated Gibbon
and Kloss's Gibbon
The Pileated Gibbon is rather extraodrinary, as males and females display sexually dimororphism, where males have a different colour fur from females. However when they are born, both boy and girl will resemble the female in fur colour, where the boy will gradually change colour. This is the only male of the Dwarf Gibbons to undergo a change
in fur colour.
In singing patterns, Dwarf Gibbons show some interesting behaviour, as among Kloss's Gibbons male will call before dawn to claim their territory, while females will call after dawn to claim theirs. A mated Gibbon with offspring will call as a group to claim their territory. When males defend their territory, the complexity and duration of their song will display their confidence and willingness
to defend their territory.
The Silvery or Javan Gibbon similarly have an interesting song structure where males will produce a simple "hoot" sound, and females have more variety in their repertoir, producing various sounds ending in a "bubble" sound. Both are known to make a screaming sound in alarm.
The Crested Gibbons
consist of the Northern Buffed-Cheeked Gibbon, Black Crested Gibbon, Eastern Black-Crested Gibbon, Hainan Black-Crested Gibbon, Northern White-Cheeked Gibbon, Southern White-Cheeked Gibbon
and the Yellow-Cheeked Gibbon.
Each Crested Gibbon knows sexual dimorphism in adults, though not yet at birth. The female is more often the one to change fur colour after birth, sometimes twice in her lifetime. This is particulaly common among Yellow-Cheeked Gibbons; males and females are born blond, and both later turn black. The male will remain black, sporting white cheeks, where the female will revert back to blond when she reaches sexual maturity. She will only retain a black cap on the top of her head.
Among these Crested Gibbons, further specifications based on DNA have been made in recent years. Formerly, many of the Gibbons of this species were considered a subspecies of another of the family, but now proved to be a seperate species, like the Hainan Black-Crested Gibbon and Eastern Black-Crested Gibbon.
The last family of Gibbons, the Hoolock Gibbons,
consists of the Western Hoolock Gibbon, Eastern Hoolock Gibbon
and the most recent addition: the Skywalker Hoolock Gibbon
This family of Gibbons is little known and researched as of yet. Only in 2005 did researchers gather enough proof to place the Hoolock Gibbons in a family of their own within the Gibbon family. Last week, news came out that a new species of Gibbon had been identified. The discovered population was first counted among the Eastern Hoolock Gibbons, but based on their song, the shape and colour of their eyebrows, their beards and DNA, the researchers found proof that they are a separate species.
Among all three Hoolock Gibbons, the males and females are sexually dimorphic, with the females being blond and the males ranging in colour from brown to black, with contrasting facial markings occurring in both genders across the species.
Some of the most endangered primates can be found among the Gibbon family. They're facing serious threats due to a small territory in some instances, where high levels of - urban - development can similarly threaten their survival. Across their habitat in Southeast Asia, Gibbons face logging, forest clearing for agriculture, and other development projects. Though Gibbons can walk across the forest floor, this leaves them more vulnerable and more likely to be caught by humans.
Gibbons have been hunted for their meat and use in traditional medicine, but recently, hunting for the pet-trade has become more common. To remove a youngster from the wild, it is almost inevitable to first kill the mother. Furthermore, development of the land will lead to fragmentation of the forest, which makes it more difficult for pairs of Gibbons with their families to survive, migrate and form new pairs.
Since several species of Gibbons overlap in the territory where they occur in Southeast Asia, this facilitates hybridisation between subspecies within the species. While in the wild there is a lack of data of the occurence of hybridisation, among captive facilities and zoos specific data of the origin is often absent, and some species look very much alike, making the occurence of hybridisation among these Gibbons likely though largely unknown.
Though the calls of Gibbons can be used to identify the species, and are used to define their territory, people hunting Gibbons are known to use the calls to locate the monkeys in the forest. As such, human activity in their territory is one of the biggest threats to Gibbons; in the wild as youngsters they mainly face threats from large to middle-size predators. Especially adult Siamangs are so large as to face little natural threats. All gibbons do further have to compete for food sources with other animals as a diet consisting mainly of fruit, leaves and flowers is not uncommon in the jungle.