Collapse of a tropical forest bird assemblage surrounding a hydroelectric reservoir

Hydroelectricity is the world's largest source of 'renewable' energy, and deployment will expand considerably in the coming decade, with Asian countries installing the bulk of new generating capacity. Before construction of large hydropower projects, empirical evidence can be utilised to inform public involvement and to realistically ground decision-making processes such as impact mitigation planning and whether or not to build. This study explored changes in avian community richness and diversity among resident forest species surrounding the 165 km(2) Chiew Larn reservoir in southern Thailand, thirty years after inundation. Replicated avian point-counts were undertaken on 23 island sites and 24 nearby mainland transects. A total of 108 habitat structure surveys were conducted. Mainland and islands were composed of remarkably similar bamboo-dominated edge habitat. (log)Area described 82% of the variability in species richness using general linear models and 74% of the variability in community composition using Bray-Curtis non-metric multidimensional scaling. Species richness was similar on mainland and islands; however, the exponential of Shannon diversity was significantly higher on the mainland. Compared to a species pool of recent confirmed records in less disturbed habitat beyond the inundation zone, one fourth of species were missing from mainland sites. The avian community was dominated by a handful of disturbance tolerant species; furthermore, several wide-spread and ecologically tolerant species were also rare or missing. The disturbance-intolerant assemblage experienced collapse. Terrestrial and other understorey insectivores, species associated with mixed-species foraging flocks, middle storey sallying insectivores, and frugivores were severely depauperate, as were Sundaic endemics and species of conservation concern. An estimated 61 km(2) of degraded edge habitat surrounded the reservoir near the study area. Without taking the potential for serious mainland edge effects and associated human disturbance of habitat into consideration, planners will underestimate the potential impact of hydropower development on avian biodiversity. (C) 2018 Published by Elsevier B.V.