Modelling the conservation status of the threatened hoolock gibbon (genus Hoolock) over its range

Habitat loss, degradation and fragmentation are major threats to all gibbon species, contributing to the dramatic decline of gibbons over the last 30–40 years. The Hoolock gibbon (genus Hoolock) in South and Southeast Asia, particularly those occurring between the Thanlwin River in the east and Brahmaputra River in the west, have been particularly impacted by these threats. We studied the extent of the remaining suitable habitat of hoolock gibbons over the species current range and identified stronghold areas for conserving remaining populations. Using logistic regression, we modelled the species presence in relation to a set of habitat variables and records to predict their probability of occurrence; threat levels were defined using a Bayesian Belief Network (BBN). Our results indicate the existence of approximately 199,447 km2 of suitable habitats forming 27 strongholds for all three species of hoolock gibbon: the western hoolock (Hoolock hoolock), eastern hoolock (H. leuconedys) and Gaoligong hoolock (H. tianxing), with 18.9% of suitable habitats facing a high level of threat, 26.2% showing a medium threat level and 54.8% exhibiting a low level of threat. Our recommendations for the conservation of remaining populations include transboundary conservation between China and Myanmar, Myanmar and India, Myanmar and Bangladesh; introduction of population monitoring and conservation awareness programmes, translocation of scattered populations; and studies on the species status in strongholds with a high probability of occurrence, but with no species abundance information.