Potential collision risk of harriers (Circus spp.) with wind turbines during the breeding season derived from high-resolution GPS-tracking

Tonio Schaub 1 ,2, Raymond H. G. Klaassen1 ,3, Willem Bouten4, Almut E. Schlaich1 ,5, Koks J. Ben1
1Dutch Montagu’s Harrier Foundation, Scheemda, The Netherlands, 2Animal Ecology Group, Institute for Biochemistry and Biology, University of Potsdam, Potsdam, Germany, 3Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, The Netherlands, 4Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands, 5Centre d’Études Biologiques de Chizé, UMR 7372, CNRS and Université de la Rochelle, Villiers-en-Bois, France

Raptors have been shown to be especially vulnerable to collision with wind turbines, but knowledge on flight behaviour characteristics affecting collision risk remains limited. In this context, high-resolution GPS-tracking represents a promising but hitherto seldom applied technique. We used UvA-BiTS GPS-tracking data to investigate flight heights and turbine avoidance behaviour of adult male Montagu's Circus pygargus (n=22), Hen C. cyaneus (2) and Western Marsh Harriers C. aeruginosus (3) breeding in the Netherlands and Germany.

The vast majority of flights occurred below 45m, the minimum rotor tip height for an "average wind turbine" (86%, 85% and 95% for the three species, respectively). For Montagu's Harriers, the probability of flying at rotor height was greatest in warm and calm weather, around noon and close to the nest, whereas no difference was found between flights inside and outside wind farms.

Harriers flew significantly less often close to turbines than expected from a null model of random flight trajectories. This horizontal turbine avoidance was more pronounced when flying at rotor height compared to below rotor height.

Our results suggest that harriers face a relatively low collision risk. However, the fact that harriers fly more often at rotor height close to their nests indicates that care must be taken in developing wind farms in core breeding areas. Finally, the tendency to build larger turbines with a lower minimum rotor tip height might be detrimental to harriers as the time flying at rotor height, and thus collision risk, increases exponentially with decreasing minimum rotor tip height.