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Kaziranga Hoolock Gibbons

Kaziranga Hoolock Gibbons

The Hoolock Gibbons are two primate species of genus Hoolock apes in the gibbon family, Hylobatidae are native to eastern Bangladesh, Northeast India and Southwest China. Hoolocks are the second-largest of the gibbons, after the siamang. They can reach a size of 60 to 90 cm and weigh 6 to 9 kg. The sexes of these apes are about the same size, but they differ considerably in coloration: males are black-colored with remarkable white brows, while females have a grey-brown fur, which is darker at the chest and neck. White rings around their eyes and mouths give their faces a mask-like appearance. Like all apes, the Hoolock Gibbons are distinctive in the great development of the arms, which are much longer than the legs. They also do not possess any tail. The long arms are actually more than double the length of its legs and are a key balancing organ without the tail associated with arboreal monkeys. A new born gibbon is covered with yellow tinted greyish white hair, but adults are black. Female adults coat colour fades to a yellowish grey. They are also sometimes called the white browed gibbons because of the white color tuft above the eyes. Gibbons are known most for their shrill calls. With the first rays of the sun, the family consisting of a group of 6-7 members starts jumping from tree to tree. It is then that one member, usually the father starts calling – a loud howl reverberating in the depths of the jungle. This is followed by calls of the other members of the family, chitchatting and progressing through the tree tops. It is believed that the name Hoolock too is is derived from the Assamese or Hindi word ‘ulluck’ meaning the loud call or howl of the gibbon. In Nagaland and Assam states of India, there was once a time when people calculated the time of the day according to the howls and hooting of the Gibbons. With the morning calls, the farmers knew it was time to go to their fields. In the afternoon when the female gibbon would make a great call which was followed by the male, people knew it was time for lunch.

Morphology & Anatomy
The Anatomy of the Hoolock Gibbons is almost very similar to that of general apes alike Orangutans and Gorillas except Gibbons have no tail. Gibbons have extremely long arms and relatively long legs. The hands are also elongated and hook shaped. The long arms and hands assist in suspensory locomotion. The thumbs are not elongated and are not used for swinging from branch to branch. They are opposable and are used for tactile probing and grooming. The body is small and typically held in an upright position. The genus Hoolock is unique among gibbons in possessing a diploid chromosome number of 38. In other gibbon genera the number is 50 (Symphalangus), 52 (Nomascus) and 44 (Hylobates), respectively. Female hoolocks appear to possess a small throat sac which may amplify the calls or some of its frequency bands which the females do produce for calling males during mating season and also for producing warning noises at large frequency during an incoming danger. Between the species, there are some morphological differences, predominantly between males with females significantly harder to distinguish visually In hoolocks, males are black, with a white unibrow (mono-brow) and a black genital tuft (around 5 cm long) males have two distinct white eyebrows and a silver or white genital tuft (around 7.5 cm. The average height of a hoolock gibbon is 81.2 cm. Females weigh around 6.1 kg while males weigh around 6.9 kg. Hoolock gibbons feed while either sitting or suspended from a support, depending on the food. During the morning in the winter, hoolock gibbons will "sunbathe" in high branches exposing their backs to the sun for several minutes at a time; In general, most of the daily activities occur between 6 and 20 m above ground level (feeding, movement, resting and calling) except social activities, which normally occur between 5 m and 27 m.

Territorial Behavior & Herd
Hoolock live in small, monogamous family groups. Typical groups consist of an adult pair with 0-4 immature offspring. Average group size ranges from 2.7 to 4. Young gibbons leave their natal group when they become adult. About talking of one observation done by some naturalists here at Kaziranga National Park, one untypical group which included two adult females (probably sisters) was unstable and ended up with one female permanently leaving the group. Like other gibbons, hoolocks are territorial. Each family group occupies a home range of about 14-55 hectares. One solitary female covers an area of about 73 ha which overlapped nearly 15% with the home ranges of three neighboring groups. On average, a group covers a day range of about 600-1200 m. Territories are defended from intrusion by other gibbons by loud morning songs and by actively chasing intruders off of the territory. Gibbon groups produce loud, stereotyped song bouts in the early morning. Songs probably serve to defend resources such as territories, food trees, partners, but may also help to attract potential mates. Gibbon songs include species specific characteristics which are inherited and not learned. Mated hoolocks typically produce duet songs which consist of coordinated vocal interactions by both partners using sex-specific phrases. In contrast to other gibbon species, however, no sex-specific note types are used during hoolock songs. Duet song bouts have an average duration of 15-18 minutes. Other family members may participate in the song bout. Solo song bouts are typically produced by unmated hoolocks only. Most song bouts are produced from preferred calling trees, mostly situated near the territorial border.

Today much of the gibbon population had been decimated and only few surviving groups are restricted to the mountainous primary forest regions straddling the boundaries of the North East regions of India and in some nearby countries of India like Bangladesh, Bhutan, Myanmar etc. Hoolocks love hill forest but now neither the hills remain nor do the forests owing to mining, roads, infrastructure development and industrial presence. Poaching is one big threat to these apes as their body parts are used as traditional medicines. Their tree-top dwelling habits are no match to complicated firearms that are killing and destructing the species. Hence there is need of serious conservation of these apes as they are the jewels of the wildlife. Mostly, Gibbons are found where there is contiguous canopy, broad-leaved, wet evergreen and semi-evergreen forests dipterocarpus forest often mountainous. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves and shoots. In India, their existence can be found mostly in North East of it, i.e. in Nagaland and in Kaziranga National Park in Assam. The hoolock is found in several types of habitats: tropical evergreen forest, the wetter tropical semi-evergreen forests, sub-tropical monsoon evergreen broadleaf forests, and sub-tropical evergreen broadleaf hill or mountain forests. The species appears to be less common in deciduous forest and scrub forest, and absent from mangrove.

Behavior & Nature
Like other gibbons, hoolock gibbons will go out of their way to avoid water and may drown if they fall into deep water. Hoolocks bask in the morning sun, especially during the cold winter season. High, leafless trees situated at the center of the territory are favored for this behavior. Like other gibbons and few apes, hoolock groups appear to have favorite arboreal pathways across the canopy of their territory which they use more frequently than other. Hoolocks exhibit strong seasonal fluctuations in their day range and activity related gestures. In the winter season, hoolocks spend more time feeding, less time traveling, their songs start later, they produce fewer song bouts, and they retire to their sleeping trees earlier than in summer. There is also mentioned seasonal fluctuations in their diet composition, and to judge by the figure published in hoolocks appear to eat a slightly higher proportion of fruits and fewer leaves in winter than in summer. At night, gibbons sleep sitting up. The family group spends the night in one of several preferred "sleeping" trees of the territory. The whole group may sleep on one or distributed over two different trees.

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