Comprehensive surveys of endangered western hoolock gibbons ( Hoolock hoolock ) in Bangladesh more than double the country’s total population estimate

The western hoolock gibbon ( Hoolock hoolock , Harlan 1834) is a Critically Endangered primate species in Bangladesh and is globally Endangered, yet its distribution across the highly anthropogenic and disturbed landscapes of southeast and northeast Bangladesh is not well understood. We assessed gibbon occurrence in habitats across Bangladesh through community engagement activities from January 2018 to June 2022 and conducted gibbon population surveys in the field from January 2019 to March 2024 using the total count method to estimate abundance in most habitats. Our results confirmed gibbon occurrence in 46 locations in 42 forest fragments in southeast and northeast Bangladesh and we estimate the current gibbon population in Bangladesh to include ≥816 individuals in ≥254 groups. Only 10 of the 42 fragments where gibbons occurred supported more than 20 individuals. Gibbons in most of these habitats are at extremely high risk of local extinction due to very small population sizes and ongoing habitat destruction, hunting, and agricultural expansion. Urgent conservation actions, including community-based conservation to combat hunting and illegal trade and to prevent further agricultural encroachment, support for monitoring and enforcement of existing laws and regulations, habitat protection, and habitat restoration programs focused on landscape-level connectivity within Bangladesh and across the Bangladesh-India border, are required to mitigate threats to the remaining gibbons in Bangladesh.