In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here’s a question from our December 2013 issue:
Why do so many birds fly into wind-turbine blades? I understand the danger of wire cables, but the blades are much wider and, I would think, easier to see. I know they go round and round, but it’s not exactly at the speed, say, of a cooling fan. – Henry Cybulski, Vilassar de Mar, Barcelona, Spain
Because of the enormous size of turbine blades, their turning speed appears slow to us as we look up from the ground but is actually very fast. The largest blades cover an area more than 300 to 400 feet in diameter, and the tips move at speeds up to 180 miles per hour.
Throughout evolutionary history, birds have flown through empty skies, often at altitudes of 400 to 500 feet — about the height of many wind turbines. It may be that birds don’t recognize the large, lethal objects as something to maneuver around.
As you note, it is not always the turbine itself that kills birds. Casualties can occur from striking the structure or associated transmission and guy wires. This may be especially true of songbirds migrating at night, when tower lights may disorient them in the same way birds become confused and strike other types of towers or buildings. Another threat to songbirds is predation from raptors that find turbine towers attractive perches from which to hunt.
The most important issue with wind turbines is proper siting. Bird mortality can be reduced by placing wind farms away from sensitive areas, such as migratory pathways and important nesting areas.
The federal government has issued voluntary guidelines for wind-farm proposals but has yet to enact mandatory rules. Several conservation organizations have best-practices guides. You can read American Bird Conservancy’s recommendations here:
About Julie Craves
Julie is supervisor of avian research at the Rouge River Bird Observatory at the University of Michigan Dearborn and a research associate at the university’s Environmental Interpretive Center. She writes about her research on the blog Net Results, and she maintains the website Coffee & Conservation, a thorough resource on where coffee comes from and its impact on wild birds.