Potential collision risk of harriers Circus spp. with wind turbines during breeding season derived from GPS tracking
Raptors have been shown to be especially vulnerable to collide with wind turbines, but knowledge on particular species-specific aspects of flight behaviour that determine the collision risk has remained limited. In this context, GPS telemetry represents a promising but hitherto seldom applied technique. I used an extensive collection of GPS tracking data, including high-resolution flight tracks (measurement interval of 3 s), to investigate the collision risk of breeding male Montagu’s Harriers Circus pygargus (MoH; n = 24 individuals), Hen Harriers C. cyaneus (HH; n = 3) and Western Marsh-harriers C. aeruginosus (MaH; n = 3) in the Dutch-German border area. First, the relevant flight behaviour characteristics were quantified separately. For MoH, these were subsequently incorporated in a collision risk model to estimate their present collision-induced mortality in the study area. Furthermore, several scenarios of future wind energy developments were studied. On average, MoH and MaH spent as much as 8.2 and 7.0 h per day on the wing, as opposed to 4.3 h in HH. The vast majority of flights occurred close to the ground, reflecting the harriers’ particular foraging behaviour. Only 7.1 (MoH), 9.6 (HH) and 3.3 % (MaH) of GPS fixes lay within the rotor height range of an average wind turbine (45-125 m). When comparing different turbine models, the proportion of time spent at risk heights increased exponentially with decreasing minimum rotor tip height (MRTH). MoH spent on average 2.0 % of time inside wind farms, and the extent of wind farm usage was negatively correlated to the nest-to-wind-farm distance. Both MoH and MaH showed avoidance behaviour, approaching turbines significantly less often than expected from a null model of random flight trajectories. The avoidance rate amounted to 94.2 and 69.0 %, respectively. For the present state, with wind farms situated in the fringes of the nesting range of the studied MoH population, the collision risk models indicated a rather low number of yearly collisions, not reaching the critical threshold of additional mortality determined from a population model. However, the erection of a new wind farm inside the inner breeding area could potentially lead to a population decline. When assuming that the wind farms would be repowered with modern, large and low-reaching turbines (rotor diameter 114 m, MRTH 36 m), the mortality would be more than doubled, whereas repowering with higher turbines (MRTH 86 m) would allow increasing the power capacity substantially without leading to a marked increase in mortality. Although my study has only a preliminary character in several regards, it demonstrates the great value of GPS tracking in the context of assessing the collision risk of birds with wind turbines and may serve as an example for future studies. The results suggest that MoH exhibit a rather low collision risk, as long as core breeding areas are kept free from wind farms. Raising the MRTH of wind turbines was shown to represent an opportunity of reducing the collision risk of the three harrier species considerably.
Windenergie, Kollisionsrisiko, Vogelschutz, Greifvögel, GPS-Telemetrie, wind energy, collision risk, bird conservation, raptors, GPS tracking
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