5. Impacts of Wind Turbines on the Population and Nest Site Selection of the Montagu’s Harrier in the Hellweg Börde, North Rhine-Westphalia

This study analyses impacts of wind turbines on the population and nest site selection of Montagu’s harriers in the Hellweg Börde. From 1993 to 2007, wind energy use increased while the number of nests decreased. No correlation between the number of turbines on the number of nests in grid cells of 4 km² was found. In areas previously occupied by harriers, only single broods occurred after the construction of turbines at a median distance of 500 m from the next turbine. No broods were found within wind farms. Nests were located in less sloping areas at larger distances from forests or settlements as well as from turbines and wind farms than to be expected randomly. In logistic regression models, an increase in distance from the next neighbour as well height and slope gradient had a negative effect, whereas an increase in distance from the next forests or settlements had a positive effect on the probability of a brood. A positive effect of the distance from the next power pylon or from the next power pylon and wind turbine combined was found in some models. These results indicate that further development of infrastructure could reduce the size of suitable habitat below the required minimum size of available open landscape. If nesting harriers do not avoid wind turbines, the risk of birds to collide with turbines will increase, because in the surrounding of the nest many flight movements (e.g. display, attacks on predators, soaring) occur within the rotor swept area.