Habitat fragmentation: Effects on endangered hoolock gibbons in northeast India

Background/Question/Methods

Effect of forest fragmentation on ranging and diet were investigated on two hoolock gibbon groups in two fragments (65 ha and 900.02 ha) of a moist evergreen forest in Assam, Northeast India. The habitat is surrounded by tea gardens and human settlements creating sharp edges. A railway tract has divided the forest into two unequal fragments, with a lone gibbon group confined in the smaller patch exposing it to very high risk of extinction.

Results/Conclusions

Habitat variables were influenced more by disturbance level than fragment size, and disturbed fragments had lower canopy continuity, food tree diversity and abundance. Home range size was not correlated to the size of the forest, but by percentage of disturbance. The gibbons in the two smallest fragments experienced a period of almost total lack of fruit in their diet at the end of the dry season. The group in the smaller fragment was forced to depend on a large amount of leaf, even in the wet season when other gibbons were eating mostly fruit. The gibbons in the more disturbed fragment spent the least amount of time in social interactions and called only intermittently during times of fruit shortage indicating that they are making trade-offs between conserving energy and investment into group bonding or territorial defence. The results of the study will influence habitat specific conservation strategies for this endangered primate species