Abstract
Do wind turbines influence forest grouse and specifically capercaillie (Tetrao urogallus)? To-date this question is much discussed and difficult to answer, as few studies are available and standards for post-constructional or Before-After-Control-Impact (BACI) designs are not always followed. The international research project “Capercaillie and wind energy” investigated six study areas in Germany, Austria and Sweden whether effects of wind turbines on capercaillie can be measured using five approaches in an BACI or post-constructional design. In Sweden, capercaillie were studied in the Jädraås wind park for a 4-year post-construction period. We addressed potential impacts of wind energy facilities (WEF) on the species’ individual and population level, by studying resource and habitat selection, movement ecology, reproduction success, risk of predation and stress physiology. We could not find significant differences in mean capercaillie sign density between WEF and control sites, nor between before and after construction sites, when analysing all European study sites. Within the WEF sites, however, habitat selection was reduced up to approximately 650 m distance to wind turbines overall study areas. Our study further revealed a decrease in resource selection within a distance of approximately 865 m around WEF (784 – 1025 m), when individual birds were tracked with GPS transmitters (N = 18) in Sweden. In addition, turbine shadow, turbine noise, turbine density, turbine visibility and turbine access roads were found to decrease resource selection, in lekking and summer season with varying magnitude. We found individual behaviour to be influenced by turbine visibility, as movement speed was discovered to slow down while wind turbine visibility increased (up to 6 WEF). The high correlation between WEF predictors (distance, shadow, noise, visibility), prevented to clearly pinpoint single factors. In contrast, additional methods addressing stress physiology, reproduction success and risk of predation did not reveal any relation to WEF. If our findings bear any fitness costs for capercaillie and affect population survival is beyond the study’s capabilities and also strongly depends on the species’ regional and national status. For Sweden, we propose to apply our estimated distance threshold of 865 m to at least capercaillie leks and summer habitats under consideration of the local forestry, to minimize the risk of negative population-level effects by the presence of wind turbines and their accompanying infrastructure. Future studies should apply reproduction and predator track monitoring on multiple impact-control areas, to underpin or reject a potential WEF influence on capercaillie populations. Finally, direct mortality of capercaillie by turbine collisions is another factor future research should try to answer.