The Pen y Cymoedd windfarm in South Wales, UK, is set in an upland area currently dominated by coniferous forestry with a varied age structure resulting from standard forestry management practices.The site supports an important population of European nightjar Caprimulgus europaeus. The activities associated with wind farm construction have the potential to damage and disturb nightjar nests during the breeding season whilst long term operation has the potential for collision mortality. To mitigate for potential impacts during construction, we implemented measures to allow nest avoidance including the identification and demarcation of active nest sites. Due to the difficulty in locating nightjar nests and the potential for false negative results, additional measures were deployed at 17 turbine locations to deter nightjars from establishing nesting territories. Deterrent measures involved regular removal of vegetation on the construction areas. We tested the effectiveness of the deterrent measures by comparing levels ofmale nightjar territorial display activity in treated and untreated locations over one breeding season.Territorial behaviour was recorded using standard nightjar presence-absence survey methods. We found no significant difference between levels of territorial display activity in treated and untreated areas. This suggests that the deterrent measures utilised at Pen y Cymoedd in 2016 were ineffective in deterring male nightjar display activity during windfarm construction
