In the last column, I reviewed some of the talks I heard at the recent Wilson Ornithological Society meeting in Massachusetts. I’ll discuss one last talk that has particular relevance to Earth Day.
Everyone is aware that carbon dioxide levels have been steadily increasing for the past 150 years. Most of this increase is due to industrialized nations, burning fossil fuels in our automobiles and coal to generate heat and electricity.
Carbon dioxide acts as a so-called greenhouse gas, trapping heat that is radiated into the atmosphere from the earth’s surface. The recent report “Climate Change 2007” by the International Protocol on Climate Change (http://www.ipcc.ch/) and the release of the movie “An Inconvenient Truth” featuring Al Gore have won over many skeptics who formerly doubted that significant global warming is occurring.
Environmentalists are ardently seeking greener forms of generating electricity that release little or no carbon dioxide. Wind power, a headline topic during the past year in Maine, offers the promise of a clean, renewable resource.
As with any technology, reasonable people can disagree about the relative costs and benefits. Opponents of wind power cite the disruption of scenic views and the noise that some turbines make as they turn in the wind. In most areas, the wind does not blow constantly, and consequently there are times when wind will be too weak to generate electricity. Hence, a wind farm will not allow less efficient generating plants to be removed from the electrical grid. Those plants will be needed to generate power when the wind is not strong enough. Wind farms in remote areas require significant lengths of roads to be built, fragmenting the landscape.
The bird and bat mortality at wind turbines is an effect that makes many question the environmental costs of wind farms. Like real estate, location of a wind farm is a critical factor in determining the number of birds and bats that are killed. Some birds may be killed by direct contact with the rotating turbines. Other birds may be disoriented at night by the lights required on all towers taller than 200 feet. The birds may fly into a tower or guy wire with lethal results.
Quantifying the number of birds and bats killed is challenging, particularly in forested landscapes. Some birds killed by turbines may fall and remain in the forest canopy. Scavengers like foxes, coyotes and burying beetles may remove killed birds before they can be found by researchers.
Wind farm proponents admit that some bird and bat mortality is inevitable. However, they argue that the reduction in carbon dioxide emissions by using the wind to generate power improves the planet for all organisms. Deciding whether it is better to approve or deny a wind farm proposal on these grounds is a question for an environmental economist. There are no easy answers.
At the Wilson Ornithological Society meeting, I looked forward to hearing Rhonda Millikin speak on her work on the response of nocturnal migrating birds to wind turbines. She has pioneered a radar-acoustic system to determine how birds and bats respond to spinning turbine blades.
She applied her technology at six wind farms in Alberta, Canada, in agricultural landscapes and one wind farm in Ontario, Canada, in a forested landscape. She tested the hypothesis that nocturnal bird and bat migrants could avoid the turbines.
Millikin measured the avoidance of turbines by looking for changes in flight behavior as birds and bats approached the blades. She found that birds were able to detect the turbines from a distance of at least 500 yards away by showing that the birds slowed their flight speed and increased their calling rate. They also flew a bit higher, rarely dipping below the height of a wind turbine. Millikin argued that birds may learn to avoid turbines.
Bats are a different story. As they approach a turbine, they climb to an altitude equal to the spinning blades and vary their flight direction. They respond quite late to the towers, often not trying to fly to safety until they are within 50 meters of the turbine. Because of their erratic flight and slow responses, bats have a difficult time traversing a line of turbines. Millikin claimed that a bat is about five times as likely as a bird to be killed when flying in the vicinity of a turbine.
Millikin ended her talk by noting particular habitats where migrating birds are reluctant to change their course. These habitats are ridges, riparian habitats and ravines or gulches with steep sides. Migrating birds have a strong attraction for these areas as they migrate and hence are less likely to avoid turbines. Wind turbines in these types of habitats pose higher risks for birds and bats.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at firstname.lastname@example.org.
21 April 2007
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