Maintaining Hornbills in the Working Landscape of the Southern Tenasserim Western Forest Complex Corridor in Thailand

Abstract

The Southern Tenasserim Western Forest Complex Corridor in Thailand is a key linkage for wildlife between prominent forests in Southeast Asia. However, it has been facing biodiversity loss due to development. To begin to address the consequences of this loss, understanding the ecology of hornbills as key seed dispersers and their ability to maintain healthy forest and restore degraded ones, is required. This dissertation explores the current state of hornbills in the region and factors that influence it, focusing on the human impacts that interrupt ecological efforts to maintain and restore the forest. I found that the quality of forest inside a large protected area in the region is comparable to other high quality habitat for hornbills in Thailand with respect to providing food and breeding sites. In this area, the smaller-sized hornbills selected nests closer to streams, at lower altitudes and in less steep areas, and in smaller sized trees than the bigger hornbills. Additionally, hornbills were able to use forest outside the protected area, but only as temporary feeding sites, because of the low density of potential fruit trees. My study documents larger foraging ranges of the immature Wreathed Hornbill (WH), which move farther from natal nests, than the smaller immature Oriental-pied Hornbill (OPH). Additionally, it reveals that the immature OPH and WH use evergreen forest disproportionately to other forest types and tend to select areas near the edges of evergreen forest. Moreover, the OPH also selects habitats at lower elevations in large forest patches. Location errors that are inherent to VHF radio telemetry may affect the results in studies using this technique. However, the resource selection models in this study were not affected by location errors. I did document that elevation, locations at lower mountainside, slope, and distance from a tracking station are factors that introduce error in calculating distances. Lastly, I developed occupancy and detection probability models for the four sympatric hornbills in the region. Hornbills respond negatively to human disturbance but positively to the availability of fruit trees, the availability of potential nest trees, and the abundance of ripe fig fruits.