Completion of the 63 square-mile (165 km2) Chiew Larn Reservoir in 1987 brought increased water storage capacity and 240 MW of hydroelectric generating capacity to southern Thailand. The project also inundated the region’s largest remaining tract of moist lowland rainforest, leaving the surrounding area permanently degraded due to deforestation and human-caused fire.

Researchers in Thailand from King Mongkut's University of Technology, Mahidol University and the Wildlife Great slaty woodpeckers are one of the birds that have largely vanished following construction of the Chiew Larn Reservoir. Source: Wich'yanan LimparungpatthanakijConservation Society assessed the impact on avian communities from the multi-purpose hydroelectric project. Forest-dependent birds have largely vanished as the contiguous rainforest has been replaced by isolated habitat patches overgrown with bamboo and vines.

More than half of the birds observed consist of a handful of wide-ranging and disturbance-tolerant species. Rainforest-dependent birds sharply declined, particularly ground-foraging and mixed-species foraging flocks, while some species disappeared altogether. Patterns of non-random avian extinction were noted across the entire study area.

The findings should inform ecological planning good practices as new hydroelectric projects are pursued in Asia. Planners should consider the potential for serious mainland edge effects and associated human disturbance of habitat to better weigh the environmental cost of hydropower development on bird biodiversity.

The study results are published in Global Ecology and Conservation.