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Massive Offshore Wind Turbines Safe for Birds

Infrared monitoring shows that savvy seabirds steer clear of wind turbines.

Uncertainty surrounding wind power’s impact on wildlife–particularly the potential for deadly collisions between birds and turbines–has tarnished its image and even delayed some wind farms. Indeed, the first large offshore wind farm proposed for U.S. waters–the Cape Wind project in Massachusetts’s Nantucket Sound–has been held up in part by concerns that its 130 turbines could kill thousands of seabirds annually. Now a simple infrared collision-detection system developed by Denmark’s National Environmental Research Institute is helping clear the air.

A heat-activated infrared video camera mounted on the turbine records deadly bird crashes on Denmark’s offshore wind farms.

The Thermal Animal Detection System (TADS) is essentially a heat-activated infrared video camera that watches a wind turbine around the clock, recording deadly collisions much as a security camera captures crimes. The first results, released this winter as part of a comprehensive $15 million study of Denmark’s large offshore wind farms, show seabirds to be remarkably adept at avoiding offshore installations. “There had been suggestions that enormous numbers of birds would be killed,” says Robert Furness, a seabird specialist at the University of Glasgow, who chaired the study’s scientific advisory panel. “There’s a greater feeling now among European politicians that marine wind farms are not going to be a major ecological problem, and therefore going ahead with construction is not going to raise lots of political difficulties.”

The Danish findings are also resonating across the Atlantic, casting doubt on worst-case scenarios presented by Cape Wind’s opponents. “The results make us guardedly optimistic,” says Taber Allison, vice president for conservation science at the Lincoln, MA-based conservation group Mass Audubon and an outspoken critic of ecological studies by Boston-based Cape Wind Associates.

TADS was developed to solve a problem specific to monitoring bird collisions at offshore wind farms, in this case the 80-turbine Horns Rev wind farm off Denmark’s North Sea coast and the 72-turbine Nysted wind farm in the Baltic. The Danish researchers at Horns Rev and Nysted used visual monitoring and radar tracking, which showed that most birds avoided the farms altogether or flew down the half-kilometer-wide gaps between the wind farms’ orderly rows of turbines. But the researchers still could not rule out the possibility that some birds were flying close enough to strike the turbine blades, which spin as fast as 80 meters per second at the tip. Of particular concern were larger seabirds, especially the common eiders that migrate through the area. “We were concerned that these large, rather clumsy birds might not be able to maneuver around the turbines,” says Danish environmental institute researcher Mark Desholm, who designed TADS.

What makes TADS practical for continuous operation is software Desholm wrote to activate recording when a warm object enters the video camera’s field of vision. According to Furness, the need to sift through thousands of hours of film was a major limitation for researchers who had previously tried infrared monitoring. He says that other automated collision monitoring that relies on vibration sensors on the blades and towers has failed to produce a reliable system. “This is the first system which has really functioned,” says Furness.


TADS was mounted on a Nysted wind-farm turbine that was situated in the most common flight path, and during more than 2,400 hours of monitoring that concluded last fall, it spotted only fifteen birds and bats and one moth flying near the turbine, and it recorded one collision involving a small bird or bat. Furness says that this provides confidence in estimations by Danish researchers that the Nysted wind farm would kill few common eiders.

The Danes’ clean bill of health is boosting prospects for the Cape Wind project because its ecosystems are similar; in particular, many of the bird species they observed also frequent Nantucket Sound. In contrast, most estimates of Cape Wind’s impact on Nantucket Sound’s rich bird life have been extrapolated from studies of onshore wind farms, leaving plenty of room for disagreement. In a draft environmental assessment issued in 2004, the U.S. Army Corps of Engineers estimated that Cape Wind would kill no more than 364 birds per year, whereas Mass Audubon argued that the data could just as easily predict mortality as high as 6,600 birds per year.

Allison says that TADS and the Danish study as a whole have now narrowed the range of probable impacts. “We certainly haven’t seen any mass mortality event,” Allison notes. A second environmental assessment for Cape Wind, expected imminently from the U.S. Department of the Interior, will include the Danish results.

Nevertheless, Allison insists that Cape Wind must perform its own studies to confirm the project’s safety. Furness agrees: “The problem of bird collisions is rather site specific. The industry would like to say, ‘Oh well, the Danes have done it, so we don’t have to worry about it.’ I don’t think that’s a reasonable approach.”

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