The Western hoolock gibbon population in Bangladesh has declined by around 84% in the past four decades thanks to deforestation, according to a recent survey published in an international journal.
The 2020 survey found that 468 hoolocks in 135 groups are now left in the north-eastern and south-eastern forests. In the 1980s, there were an estimated 3,000 hoolocks in Bangladesh.
As noted in the survey, Moulvibazar's Rajkandi Reserve Forest has the highest number of 122 hoolocks, some of the forests that were previously known as the home of the apes now have none.
Sabit Hasan, a member of the survey team, said, "Indiscriminate deforestation, food shortages and poaching are the main reasons for the decline in the hoolock population. In Chattogram and Chattogram Hill Tracts, people hunt the apes."
The survey was conducted in 22 forests in Sylhet and Chattogram from March 2019 to February 2020. During the survey, the wildlife researchers covered around 204km of forestland to gather information about hoolock gibbon, which is an endangered wildlife species globally and critically endangered in Bangladesh.
Researchers say the ape species plays a crucial role in seeding dispersal and forest regeneration.
The findings of the survey – conducted in association with the Bangladesh Forest Department and funded by the US Fish and Wildlife Service – were published in the Diversity Journal this month.
The surveyors say hoolock populations in six forests in Sylhet division are quite good. Around 120 hoolocks were found in Rajkandi Reserve Forest in Moulvibazar, 91 in Patharia Reserve Forest, 40 in Lawachhara National Park, two in Sagarnal Forest, five in Rema-Kalenga Wildlife Sanctuary in Habiganj, and nine in Satchhari National Park.
The survey also covered 18 forests in Chattogram division, including Dighinala forest, Sajek Valley, Pablakhali Wildlife Sanctuary, Hajarikhil Wildlife Sanctuary, Sangu-Matamuhuri Reserve Forest, Ramu and Thanchi.
In the course of the survey, researchers found that the sizes of the ape population are better in reserve forests than in less protected or totally unprotected forests.
In the maiden survey in the 1980s, Bangladesh's forests were estimated to have 3,000 hoolocks. The number drastically declined to only 200 in the 1990s. In the third survey in the 2000s, 282 apes were estimated to be in the country.
Apart from Bangladesh, Sabit Hasan said, hoolocks are also found in India, Myanmar and China. There are 19 species of apes in the world and South Asia is home to three of them. In Bangladesh, only Western hoolock gibbons are found.
Habibon Naher, associate professor at Jagannath University and the lead researcher, said most of the hoolocks the team found were in Rajkandi and Patharia Reserve Forest in Moulvibazar.
She said hoolocks were not found in some of the forests, such as Hajarikhil, that previously were inhabited by the apes.
"Hoolocks have either moved elsewhere or have gradually gone extinct [in these forests] due to development work and human aggression," she noted.
Hoolock is an omnivorous animal and fruits make up 65% of its diet, with 60% of the fruits being figs. They also eat lichens, invertebrates, bird eggs, plant parts (buds, shoots, leaves, flowers), and insects. Since they have a wide variety of fruits on the diet chart, they cannot live in monoculture or in homogeneous forests.
Hassan Al Razi, the survey manager, said all the forests where hoolocks were found are like small islands – isolated from one another.
Referring to the highest hoolock population in Patharia and Rajkandi forests, Tanvir Ahmed, a member of the survey team, said it is important to take steps to declare the forests as hoolock sanctuaries.
Divisional Forest Officer Rezaul Karim Chowdhury said it is good news that Patharia and Rajkandi forests have large hoolock populations. "I will talk to my superiors and try my best so that the forests are declared as hoolock sanctuaries."