Vogelbescherming's declaration is based on research carried out by biologist Joke Winkelman. In the period between 1992 and 1994 she counted the number of birds killed by wind turbines in the former Oosterbierum wind farm owned by utility SEP. On average, the 18 turbines caused one bird death a day. From this study and other similar studies in northern Europe, Winkelman expects that an installed capacity of 1000 MW in the Netherlands would result in 21,000 dead birds a year.
This death rate compares with about one million bird deaths in the Netherlands caused by power lines and antennas; one and a half million birds killed by wildfowlers; and nine million killed in traffic in the Netherlands alone.
Birds which collide with wind turbines are mainly common species which get caught in rotor turbulence, she says. At Oosterbierum the main species found dead was the black headed gull (Laris ridibundis) and the common starling (Sturnus vulgaris).
More important for the well being of birds than the death rate, though, is the impact wind turbines might have on their natural habitat, including noise disturbance, says Winkelman. This has an impact not only on brooding behaviour, but also on trekking and feeding, with trekking birds probably suffering most.
But birds that live all their life in the neighbourhood of wind turbines seem to get used to them and their noise, while some even adapt their behaviour to use the wind turbines to their advantage. Winkelman has seen a peregrine (Falco peregrinus) fly between the turning blades to attack a confused victim.