A study commissioned by the Royal Society for the Protection of Birds (RSPB) found that many species of birds avoid nesting in areas within 500 meters of wind turbines.  The RSPB, like its US conterpart the Audubon Society, has been largely supportive of wind energy.  The new study was the most detailed yet of bird distribution around wind farms: twelve major upland wind farms were surveyed six times during the breeding season for a dozen common species including waders and gamebirds (golden plover, lapwing, curlew, snipe, red grouse), raptors (buzzard, hen harrier, kestrel), and songbirds (skylark, meadow pipit, stonechat and wheatear).  Of the 12 species studied, 5 seemed undisturbed, while populations of 7 were 15-53% lower when within 500m of a wind turbine.  The displacement effects continued out to a distance of about 800m (roughly a half mile).  The affected species were buzzard, hen harrier, golden plover, snipe, curlew, wheatear and meadow pipit.

Image from The Telegraph; click to read article

It is crucial to note that this study was looking at nesting patterns, and does not suggest that birds are being killed by the turbines, but rather that they avoid nesting near them, presumably because of increased noise, which could disrupt communication between birds or reduce the amount of prey and make it more difficult to hunt (whether for insects or rodents).

UPDATE: I recently came across a paper from last year that found no obvious avoidance of wind farms by most wintering species of UK farmland birds.  This paper looked not at nesting patterns during breeding season, like the paper above, but rather at wintering birds’ presence (they walked randomized paths, and counted birds seen; most were seen when flushed from the grain).  Looking at numbers seen in 5 sets of distances (from 0-150, to 600-750m), wintering farmland birds (seed-eaters, corvids, gamebirds and Eurasian skylarks) showed no increase with increasing distance. A further investigation of 0-75m and 75-150m also showed no trend.  Only pheasants showed a tendency to be found in the segments further from turbines.