Birds often collide with high voltage overhead lines, masts, poles and windows of buildings. They are also killed by cars in the traffic.
Birds are seldom bothered by wind turbines, however. Radar studies from Tjaereborg in the western part of Denmark, where a 2 MW wind turbine with 60 m rotor diameter is installed, show that birds - by day or night - tend to change their flight route some 100-200 m before the turbine and pass above the turbine at a safe distance.
In Denmark there are several examples of birds (falcons) nesting in cages mounted on wind turbine towers.
The only known site with bird collision problems is located in the Altamont Pass in California. Even there, collisions are not common, but they are of extra concern because the species involved are protected by law.
A study from the Danish Ministry of the Environment says that power lines, including power lines leading to wind farms, are a much greater danger to birds than the wind turbines themselves.
Some birds get accustomed to wind turbines very quickly, others take a somewhat longer time. The possibilities of erecting wind farms next to bird sanctuaries therefore depend on the species in question. Migratory routes of birds will usually be taken into account when siting wind farms, although bird studies from Yukon show that migratory birds do not collide with wind turbines.
Birds and offshore wind turbines
Offshore wind turbines have no significant effect on water birds. That is the overall conclusion of a three year offshore bird life study made at the Danish offshore wind farm TunÝ Knob. The offshore wind park has been placed in this particular area because of a very substantial population of eiders (Somateria mollissima) and a small population of scoters (Melanitta nigra). At TunÝ Knob more than 90% of the birds are eiders, and about 40% of the North Atlantic population of eiders are wintering in the Danish part of the Kattegat Sea.
The Studies were conducted by the National Environmental Research Institute at KalÝ, Denmark.
In the figure, Ornithologists' (Bird watchers) tower erected next to the offshore wind farm at TunÝ Knob, Denmark, for a three-year avian study which were completed in 1997.
Controlled experiments stopping the wind turbines for a certain period has been performed. In another experiment decoys was used to attract the eiders, which are very social birds.
The result of the experiment using groups of decoys at different distances from the wind farm showed that the eiders were reluctant to pass at distances of 100 m or closer to the turbines.
The on/off experiment showed that there was no detectable effect of revolving rotors on the abundance of eiders in the area. In fact the eiders - like people - apparently prefer rotating turbines (but that result was clearly insignificant).
The overall conclusion of the final two experiments were that on one hand the eiders do keep a safe distance to the turbines, but on the other hand they do not get scared away from their foraging areas by revolving rotors. Also, the eiders showed normal landing behaviour until 100 m from the turbines.