The Eastern hoolock gibbon (Hoolock leuconedys) is a species of lesser ape native to subtropical and tropical forests of northeastern India, Myanmar, and southwestern China, recognized for its distinctive vocalizations and striking sexual dimorphism.
Formally described by Groves in 1967 from northeastern Myanmar, the Eastern hoolock gibbon was once considered a subspecies of Hoolock hoolock but is now widely accepted as a distinct species. It belongs to the genus Hoolock, which diverged from other gibbon genera within the family Hylobatidae, marking its unique evolutionary lineage in the lesser apes.
The Eastern hoolock gibbon is classified within the superfamily Hominoidea, family Hylobatidae, and genus Hoolock. As a lesser ape, it shares the family with other gibbons but is distinguished from great apes by its smaller size and arboreal lifestyle. Its species status is supported by multiple taxonomic authorities including the IUCN and Mammal Species of the World.
This species exhibits pronounced sexual dimorphism: adult males have black fur accented by distinctive white brows, while females display lighter buff or grayish pelage with a dark facial mask. Adults typically measure 45 to 65 centimeters in body length and weigh between 6 and 9 kilograms. Adapted for life in the trees, their long arms and agile bodies enable skilled brachiation through forest canopies.
The Eastern hoolock gibbon is diurnal and arboreal, moving gracefully through the forest canopy by brachiation. It lives in small family groups, usually monogamous pairs with their offspring. Their complex, species-specific vocalizations serve important roles in territory defense and mate attraction, reflecting sophisticated social communication.
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Native to subtropical and tropical broadleaf forests, the Eastern hoolock gibbon occupies elevations from 200 to 2,500 meters. Its range spans northeastern India, Myanmar, and southwestern China, where it depends on intact forest canopies for movement and survival.
Typically, Eastern hoolock gibbons live in small family groups composed of monogamous pairs and their offspring. Their social interactions are reinforced by complex vocalizations used for territory defense and mate attraction, highlighting a close-knit and communicative social system.
While specific dietary details are limited, like other gibbons, the Eastern hoolock gibbon is primarily frugivorous, feeding on a variety of fruits supplemented by leaves, flowers, and occasionally insects. Its arboreal lifestyle facilitates access to diverse food sources within the forest canopy.
Classified as Endangered, the Eastern hoolock gibbon faces significant threats from habitat loss and fragmentation due to logging, agriculture, and infrastructure development. Although protected under national laws and listed on CITES Appendix I, occasional poaching for bushmeat and traditional medicine persists, further endangering populations.
Genetically, the Eastern hoolock gibbon is part of the genus Hoolock, which diverged from other gibbon genera such as Hylobates, Nomascus, and Symphalangus. No hybridization events with other gibbons have been documented, though species delimitation within Hoolock leuconedys remains an active area of research.
