Fragmented populations of the Vulnerable eastern hoolock gibbon Hoolock leuconedys in the Lower Dibang Valley district, Arunachal Pradesh, India

Abstract

We conducted a survey of the distribution and population status of the eastern hoolock gibbon Hoolock leuconedys in non-protected fragmented forest areas of the Lower Dibang Valley district of Arunachal Pradesh, India, during September 2010-June 2011. We estimated the minimum population density at seven study sites by direct observation and by counting the number of vocalizations heard from groups that were out of view. We used 1-ha belt transects (500 × 20 m) to estimate tree diversity in the study area. For two groups of gibbons we recorded their feeding patterns in forest fragments, using focal individual sampling, during May 2011. A total of 54 groups and three solitary individuals were recorded: 39 groups and three individuals through visual encounter and 15 groups through vocalization recognition. The mean group size recorded was 2.89 ± SE 0.11 (range 2-4). We counted a total of 289 trees, of 26 species and 17 families, in 18 belt transect surveys covering all non-protected fragments of the Lower Dibang Valley district. The gibbons' diet consisted of seasonal fruits and figs (29%), leaves (65%), seeds (2%) and flowers (0.5%). The major threats recorded at the study sites were habitat destruction and hunting. To protect the Vulnerable eastern hoolock gibbon, conservation measures will need to involve local communities.