I suspect that overall, the problems in terms of biodiversity loss to birds and bats from coal and natural gas power is more important than direct deaths from collisions with windmills, but how bad is that? Thanks to Oliver and Kelly for sending references on the subject.
On one side of the debate are those who say that windmills are not so harmful to birds. Industry reports most studies have found few bird kills (the Altamont Pass in CA is an exception), and that there are more significant dangers to birds (though they don’t distinguish between endangered species and more common species). They correlate higher risks with some areas and some types of turbines, but give no details. They also report briefly on bats.
Dead Raptor in Altamont Pass
National Renewable Energy Laboratory, or at least some researchers at same, agree. Brian Parsons (Some Common Misconceptions about Wind Power, pdf) addresses only the bird portion of the question:
Wind turbines kill birds and thus have serious environmental impacts.
Responses:__ Bird kills have caused serious concern at only one location in the U.S.: Altamont Pass in California. This is one of the first areas in the country to see significant wind development. Over the past decade, the wind community has learned a great deal about siting wind plants in ways that avoid locations that might pose problems for birds. Modern wind installations are simply not raising avian concerns.
__ One to two bird kills per turbine per year is at the high end of the range observed in U.S. wind installations. The majority of deaths are common species. Compared to bird deaths resulting from other manmade structures, highway traffic, and housecats, bird kills by wind plants are numerically insignificant and are not expected to impact bird populations. Of course, deaths of endangered species are of greater concern, but again the only location with a suggestion of this problem is Altamont. And even in that case, experts disagree on the severity of the problem.
__ Environmental impacts are relative. All energy technologies have some negative environmental impacts. Society makes tradeoffs when making power plant choices. Wind plants may result in some bird fatalities or other unwanted impacts on wildlife and their habitats. Coal plants cause premature human deaths from respiratory problems. Maintaining open channels for free flow of oil causes military deaths. Society needs to choose from these alternatives, and it cannot assess a single energy technology in isolation.
It is absolutely true that we need to compare the total advantages and disadvantages of each technology in choosing among them.
Other analyses have now shifted my thinking from skeptical to open minded.
Audubon in CA hosted a conference, you can see their reports here.
The following comes from a California Energy Commission 2005 report, Asessment of Avian Mortality from Collisions and Electrocutions (pdf)
The conclusions are relevant for CA, which appears to have the most bird problems with windmills (Altamont Pass has the most problems in CA).
From the Summary of Staff Findings and Policy Options
Most Bird Species Killed by Interactions with Wind Turbines or Electrical Power Line Infrastructure are Protected by Federal and State Laws and Regulations.
The California Energy Commission (Energy Commission) Could Promote Development of New Wind Resources Only in Areas That Have Low Risks to Birds.
The Energy Commission Could Support Statewide Guidelines Requiring the Wind Industry to Mitigate Its Impacts on Birds in the State.
In the Altamont Pass Wind Resource Area, the Energy Commission Could Encourage Industry to Apply Mitigation Measures to Existing Projects, New Projects, and Repowering Projects to Reduce Bird Deaths—Ultimately, implementing mitigation could allow industry to expand if Alameda County was able to lift its moratorium because of a reduction in bird kills.
The report also suggests much better monitoring of bird and bat kills across the state, and a shift from voluntary to mandatory guidelines.
