Are Building Integrated Wind Turbines Safe for Birds?

Although bird safety issues with large, horizontal axis wind turbines are rare, these incidents have been widely publicized.  So it is natural for building owners to wonder whether wind turbines are safe for installation on their building. There are several factors which make wind turbines safer for birds in building integrated applications versus wind farms.

Large horizontal axis wind turbines have blades in excess of 30 ft in diameter.  The tips of the blades are moving many times faster than the central hub due to the large diameter.  The resultant image of the wind turbine is one that looks solid near the hub and gradually becomes transparent towards the blade tips, which probably leads to more bird fatalities. 

Wind turbines used in building integrated applications are much smaller than turbines on utility scale wind farms.  Due to the smaller size of building mounted wind turbines, the blade tip speed is inherently slower, so the entire wind turbine looks like a solid object to the birds.

Wind farms are often located in mountain passes due to the available wind resources, which are often also used as migratory paths by birds.  Wind turbines are often widely spread out in open fields to maximize the exposure to wind.  As a result the wind turbines are spinning at the height of the migratory bird's flight path.

The National Audubon Society, a professional organization whose main objective is the protection of birds and other wildlife and their habitat, published a statement in 2001 expressing their belief that small-scale wind turbines do not pose a significant threat to bird population, and showing their support for the California Assembly Bill AB 1207, which encourages the use of small-scale wind turbines that produce approximately 50 kW or less.

"We do not feel that there is any significant threat to bird population from small-scale wind turbines, and are pleased to support your AB 1207."

-Extracted from the original Audubon Letter, 2001.