Ape is a word that means tailless monkeys and when we talk about apes the animal that comes is our mind is generally Gorillas and Chimpanzees but very few of us know that in India we also have a species of ape that is ‘Hoolock Gibbon’. Earlier there was only one species which was called Hoolock Gibbon but later studies have suggested that there are two species, i.e. Western Hoolock Gibbon and Eastern Hoolock Gibbon, we will discuss the differences and similarities later.
Gibbons of the World
The apes of the world are divided into two major categories the great apes and lesser apes, while all Bonobos, Chimpanzees, Gorillas and Orangutan come under the great ape’s category, all Gibbons and Siamangs come under the lesser ape category. There are 20 species of gibbons in four genera in the world and all of them are endemic to South and South-East Asia. They are the most primitive among the living apes, the gibbons are separated from other hominids (a group consisting of all modern and extinct great apes and humans) about 18 million years ago. They are diurnal and arboreal in nature and need close canopy undisturbed evergreen and semi-evergreen tropical forests as their habitat. Gibbons show little sexual dimorphism based on size but the same is pronounced on the body pelage. All gibbons are monogamous, which means they remain in the same pair throughout their life. Hainan Crested Gibbon (Nomascus hainanus) is the rarest and most vulnerable of all primate species. Only less than 30 individuals are left in the wild and a range is restricted to only 2 sq. km. on an island on the southern tip of China.
The Hoolock gibbon is a tree-dwelling, monogamous (same partner throughout the life), and territorial ape. The male and females have different body colour. Males are black while females are light brown in colour. Infants are born with a pale white pelage, which later changes to black at about the age of two years. Males retain the black colour while female changes it again at the onset of puberty, around 6-8 years in age. In India, two species of Gibbon are found.
- Western Hoolock Gibbon (Hoolock hoolock)
- Eastern Hoolock Gibbon (Hoolock leuconedys)
Western Hoolock Gibbon
They are found in Assam, Arunachal Pradesh, Nagaland, Tripura, Meghalaya, Mizoram, and Manipur. They are widely distributed and found in Bangladesh and Myanmar too. They are the second largest gibbon in the world after Siamang. The adult male have a completely black body with continuous white eyebrows, a short pointed beard, and a black or dark brow genital tuft 2-3 inches long. The adult females are light brown with a whitish ring around the eyes and muzzle.
Eastern Hoolock Gibbon
They are not so common in India and only found in Dibang Valley in Arunachal Pradesh and Sadiya Reserve Forests of Assam. Apart from India, they are found in Myanmar and China too. The adult male of the Eastern Hoolock Gibbon differs from the Western Hoolock gibbon in having a white or light color genital tuft, the eyebrows are not continuous but have gap in the middle and white chin hairs, while the adult females have hands lighter than their body color.
Both species of Hoolock Gibbon are given the vulnerable status by International Union for Conservation of Nature (IUCN) , Western Hoolock Gibbon has most recently been assessed and it has been given the vulnerable status, earlier it was endangered.
Population Estimate of Hoolock Gibbon
There is no recent population estimate available. In 2005 Molur estimated the total population of Western Hoolock Gibbon in North-Eastern India which is around 12000 out of which 2000 was estimated for Assam alone. The Population of Eastern Hoolock Gibbon in India was estimated in 2006 in the Mehao Region of Eastern Arunachal Pradesh to be 170 individuals.
Habitat of Hoolock Gibbon
Gibbons inhabit tropical and subtropical wet evergreen, semi-evergreen forests, moist-deciduous forests, and broadleaf hill forests with a hot wet summer and a cool dry winter. They spend almost their whole life on trees and are known to brachiate from one branch to another branch, one tree to another tree. This unique habit makes them an acrobat of the canopy which requires close canopy forests for their smooth movement. It was observed that during territorial chases males come down on the ground where the canopy is broken. On the ground, they are vulnerable to attack by predators.
Home Range of Hoolock Gibbon
Their home range sizes depend upon various factors and one of the factors is fragmentation and isolation of suitable habitat. It is observed that fragmented habitats have smaller home ranges while undisturbed forests have larger ones. Another and most important factor for home range size is the available resources. The average home range size is between 22 and 35 ha. The selection of home ranges depends upon the availability of food even during the season of scarcity.
They defend their home range as an exclusive territory by loud calls and occasional confrontations and chases. This type of confrontation is mostly observed in adult and sub-adult males.
Day Range of Hoolock Gibbon
The distance traveled by Gibbons from one sleeping site to another in a day is called the day range, it can be as minimum of 100 meters or 5000 meters. They travel during the day so the duration will be short in winter while it is longer during summer and monsoon. They travel on the designated old canopy pathway through the same trees.
Daily activity of Hoolock Gibbon
The active hours for Hoolock Gibbon range from 9-12 hours on average. They wake up early in summer and go to sleep late but in winter they wake up late and sleep early. Female in the group wakes up early and followed by the rest of the group and then they defecate and urinate and then they go to the tree from where they had food the previous day, this first feeding lasts for about two hours. They sing and then move to the other tree for feeding. They have three feeding peaks during the day after which they move to the sleeping site. Usually sleeping tree is very tall dipterocarp with horizontal branches. They sleep in a sitting position, and females with infant sleep alone.
Diet of Hoolock Gibbon
Hoolock Gibbons are primarily frugivorous (Fruit Eating) unlike Siamang who are primarily folivorous. They have a very simple stomach and feed on fruits and figs that are easily digestible. In forest ecosystems they play the role of seed dispersers, the ingested seeds are rarely digested and excreted whole. They also consume young leaves and insects as a protein source. Figs form the largest percentage of fruits consumed by them.
Having complete arboreal life they rarely come down on the ground to drink water mostly they drink water which is collected in the holes on tree trunks by dipping their hand and licking it off.
Hoolock Gibbon Song
The adult gibbon pair sing a loud and elaborate song in the form of a duet. Sometimes juveniles and young ones also join. The average duration of the song is 15-20 minutes. The main function of the song is to defend the territory by vocal means. Songs of solo gibbon serve as an advertisement for mates. Generally, a Hoolock Gibbon group sings at an interval of 1-3 days. They call in all weather conditions except heavy rain and fog. When alarmed or disturbed they produce a short croak.
Hoolock Gibbon Reproduction
Hoolock Gibbons attain sexual maturity between 6-8 years of age. The menstrual cycle is of 28 days. The mating has been observed from March to October between resident males and females. There are very rare cases of mating outside the established pair. The gestation period is 183 – 225 days in captivity. They give birth to a single child. There is a winter birth peak between mid-September and February. The inter-birth interval is in between 2 and 3 years. The infant is nursed by the mother till it attained the age of two years. At the age of 2.5 years, the infant becomes fully independent young Hoolock Gibbon.
Interaction with other primate species
Though the area where Hoolock Gibbons are found have a diversity of other primates like Slow Loris, Assamese Macaque, Rhesus Macaque, Pig Tailed Macaque, Stump Tailed macaque, Capped Langur and Phayre’s Langur, the interaction among them are normally peaceful. The resource sharing is observed adopting different canopy layer.
Hoolock Gibbon Predator
Having a predominant arboreal life they have fewer predators compared to terrestrial primates. Common leopard, Clouded Leopards, Pythons, and large birds of prey are their predator. Near human habitation, it was observed that dogs predate on gibbons that are forced to come on the ground. In the wild, their average life span is around 20-25 years while in captivity they may live upto 40 years of age.
Gibbons are a very effective seed disperser. Having fruits as their major diet they ingest seeds with the fruit which rarely digest and come out as a whole. They are covered in the excreta which provides good substratum and moisture to the seed to grow and hold the ground fast.
Best Place to see the Hoolock Gibbon
There are several places where they can be seen very easily, Kaziranga Tiger Reserve, Hollongapar Gibbon Wildlife Sanctuary, Borajan Bherjan Padumoni Wildlife Sanctuary complex in Assam are the best places to see Western Hoolock Gibbon while Mehao Wildlife Sanctuary in Arunachal Pradesh is the best place to see Eastern Hoolock Gibbon.
How to Reach
Borajan Bherjan Padumoni Wildlife Sanctuary Complex: Nearest railway junction is Tinsukia which is 6 km. (30 Minutes) and the airport is Dibrugarh Airport which is about 40 Kms. and takes an hour to reach.
Gibbon Wildlife Sanctuary: The nearest airport and major railway station to Gibbon Wildlife Sanctuary is Jorhat, which is only 25 km. From the sanctuary, in Gibbon wildlife sanctuary one can spot seven different species of primates in a small 20sq. km. area.
Kaziranga Tiger Reserve: The nearest airport is Jorhat which is 105 km. ((2½ hours) from Kaziranga. Another airport that has more flights connected is Guwahati which is 225 km. (4½ hours) from the reserve.
Mehao Wildlife Sanctuary: Nearest Railway station is Tinsukia which is 102 km. (2½ hours) from the sanctuary. The nearest Airport is Dibrugarh which is 143 Km. (3½ hours).
Best time to see the Hoolock Gibbon
It is not easy to spot them in a dense canopy of wet evergreen forests when they are sitting motionless. They are quite easy to spot when they are on the move from one tree to another. They are mostly active during the daytime and less active when it rains, so avoiding the rainy season any season is good, but I recommend winter because it’s less humid, has fewer chances of rain, easy to spot due to fewer leaves in deciduous trees, and easy to walk in the otherwise hot and humid forests. November to March is a good time to observe them and other primates.
Conservation Issues of Hoolock Gibbon
Fragmentation of forests and isolation of habitat are one of the major issues including hunting and capturing for bush meat and the pet trade. Shifting cultivation was practiced in North East India on a large scale which has destroyed a large amount of their habitat.