Calculation of the Probability of a Collision of Territorial Birds of Prey with Wind Turbines

Abstract

To estimate the collision probability of red kites and Montagu’s harriers depending on the distance between wind turbines and nest, the results of telemetric monitoring of these two species were modelled following Band et al. (2007). The basic idea of the Band model is to determine three components: I—the frequency of flights through the rotor swept area of a wind turbine, II—the probability of a collision of the bird with the rotor in these flights and III—the avoidance behaviour of the bird in the immediate vicinity of the rotor. For the latter factor only few reliable data were available and absolute values of the collision risk were therefore subject to a high level of uncertainty. Within a species these values were still comparable. Collision probabilities were calculated for different distances between wind turbines and nest. Several sample turbines could be compared for Montagu’s harriers (small E-40 wind turbines, 500 kW; medium E-66 wind turbines, 1800 kW; large V90 wind turbines, 3000 kW). The results relate to one turbine only per distance class. For the Montagu’s harrier results showed an increased estimated collision risk within a distance of below 300 m between nest and wind turbine. The absolute collision risk in this close-up area around the nest was largest for small wind turbines and significantly higher than for the two larger wind turbines. For red kites the estimated collision risk was substantially higher than for Montagu’s harriers. For red kite too, the collision risk was highest with wind turbines in the vicinity of the nest. Lower values were reached from a distance of 1250 m. The results show that a minimum distance kept between wind turbines and red kite nests will considerably reduce the collision risk. This is also true for the Montagu’s harrier with a collision risk mainly occurring in the close-up area of the nest. For this species a standardised distance recommendation will not be practicable, as Montagu’s harriers choose a new nesting site every year. Definition of breeding areas outside the main breeding areas existing in Germany will hardly be possible.