Source: Erickson, et.al, 2002. Summary of Anthropogenic Causes of Bird Mortality. A study done in the US; at the time, there was 4.5 GW installed, and a few eighties parks, especially Altamont Pass, were responsible for most birdkills. So even if wind is developed in the extent I calculated in reply to asdf (i.e. a 400-fold increase on 2002), birdkills will stay below that of any other significant causes.

_{*Lunatic*, n.
One whose delusions are out of fashion.}