The science of avian collisions with wind turbines continues to demonstrate, despite the concerns of some conservation groups, that the threat to birds from turbines is modest compared with other human structures and activities.
A recent paper by Kerlinger et al appearing in The Wilson Journal of Ornithology examines the effect of different types of turbine lighting on night-migrating bird collisions. While the paper's ultimate conclusion is that either red or white flashing lights are safer for night migrants than steady-burning lights (which many believe can disorient birds on foggy nights), the paper also includes a number of statements pointing to the relatively small role that turbines play in avian mortality.
While the authors note that "Songbirds often collide with communication towers, lighthouses, skyscrapers, and other structures during nocturnal migration with fatalities, at times, numbering in the hundreds or even thousands of birds in a single night," they write that only four multi-bird fatality events (more than 3 birds) have been reported at wind turbines–and even those all occurred at turbines with non-standard or ancillary lighting. (The most serious, with about 27 songbirds reported killed, occurred on a foggy night at turbines next to a substation where very bright sodium-vapor lights had been left on all night.)
Examining studies from 30 wind farms (including more than 25,000 searches for fatalities), the authors found that " … fatality rates at these structures are relatively low, ranging from ~1 to 7/turbine/year … What is striking about the data from wind farms is the relative absence of large-scale fatality events, similar to those recorded at tall communication towers supported by guy wires, where collisions of hundreds of birds at times occur in a single night … That so many studies and so many searches have been conducted at wind turbines without recording large-scale fatality events strongly suggests the probability of large-scale fatality events occurring is extremely low."
Communication towers with guy wires and a combination of steady-burning and flashing lights, the article said, have night migrant fatality rates "one to two orders of magnitude [10 to 100 times] greater than wind turbines … We strongly suggest that reported fatalities of night-migrating birds are minimal at wind turbines based on results reported for communication towers … , especially when compared to tall, communication towers with guy wires."
"Night Migrant Fatalities and Obstruction Lighting at Wind Turbines in North America" is designated as being from The Wilson Journal of Ornithology 122(4):744–754, 2010.