The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Gibbon density in western Thailand: The influence of altitude and forest type


1Anthropology, The University of Texas at San Antonio, 2Conservation Ecology Program, King Mongkut’s University of Technology Thonburi, Bangkok

March 28, 2015 , Gateway Ballroom 2/3/4/5 Add to calendar

The Huai Kha Khaeng Wildlife Sanctuary (HKK) in western Thailand is remarkable for the fact that evergreen, mixed deciduous, and deciduous dipterocarp forest (DDF) occur within only a few hundred meters of each other across a range of altitudes. To explore the relationship between forest type and gibbon group density we conducted vocal surveys of gibbons (Hylobates lar) from February 2012–August 2013. We predicted that there would be a negative correlation between gibbon density and DDF, due to fruit scarcity.

We established 31 pairs of listening posts along main roads throughout the sanctuary and over 3-5 days/post recorded the total number of great calls detected and estimated the number of distinct groups heard/day. We used Distance 6.0 to calculate gibbon density and the effective detection radius (EDR). Within each listening area (A=πEDR2) we calculated the percent of DDF based on satellite imagery. Mean altitude for each listening area was derived by superimposing a 100m grid and averaging the altitude of all grid intersections.

The EDR across all posts was 862m and the combined density was 2.9 groups/km2. Contrary to expectations there was no correlation between forest type and gibbon density (p>0.05), though there was a significantly positive correlation with altitude (r=0.60, n=31, p<0.001). These findings may indicate that gibbons occupying areas with high amounts of DDF are able to compensate for low fruit abundance by switching to alternative resources such as flowers or insects, which would have important implications for gibbon conservation. The role of altitude is also discussed.

Funded by The University of Texas at San Antonio Collaborative Research Seed Grant Program.