permaculture

[Saor Stetler <saor@ycbtal.net>]

     Common Eco-Myth: Wind Turbines Kill Birds


   April 6, 2006 07:01 AM - John Laumer, Philadelphia
   <http://www.treehugger.com/authors/index.php?author=John%20Laumer>

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It's a given that anytime we post a story on wind power someone is going 
to comment that "turbines kill birds," suggesting that wind power may 
therefore be unacceptable. Compared to what? Hitting birds with 
automobiles (along with turtles, groundhogs, and deer)? Birds caught by 
feral cats? Birds colliding with buildings or phone towers? Quite 
possibly, a higher mortality will be attached to the transmission wires 
needed to get the wind power to market. Why, then, do many associate 
bird mortality only with wind turbines? We hope to get to the bottom of 
this "death by turbine" myth hole, and point to the factors that can 
actually be managed though public involvement.

Our hunch is that the Altamont Pass California wind turbines, reportedly 
the site of some of the highest bird mortalities associated with any US 
wind farm, and using what is now an antique turbine design, are at the 
root of the widespread association of bird mortality with wind turbines 
in general. Now might be a good time to have a glance at this site, to 
get some perspective on the hundreds of raptors killed per year by the 
Altamont turbines.

If extrapolating the "worst case" rate is a bad idea, what about the 
"average" wind farm bird mortality figures? Even average rates, which 
are much lower or course, need to be looked at carefully.

To help our understanding of turbine hazards to birds we'd like to make 
an analogy, to your bicycle. Turn your bike upside down or put it in a 
work rack, set it to the highest gear...the one you use to go fast on a 
level slope.... and now move the wheel slowly with your hand. The chain 
moves rapidly with only a few degrees of wheel rotation. This symbolizes 
today's cutting edge 1.5 mW turbines, which have a very large surface 
area of blade exposed to the wind and a gearbox that turns the dynamo 
quickly while the blades move slowly. Birds dodge these slow moving 
blades relatively easily.

Now put the bike in the lowest gear...the one you use to climb 
hills...and move the wheel with your hand fast enough to turn the chain 
as fast as before. That symbolizes the 20-year-old "bird-o-matic" wind 
turbine design. Small blades with small surface areas have to turn 
rapidly to overcome the magnetic force of the dynamos, which generate 
electricity.

Recapping: small blades, low surface area, lots of dead birds possible; 
very big blades, with large surface area exposed to wind, very few dead 
birds.

High capacity turbines are a relatively recent commercial product. 
Consequently, any field study of "avian mortality" done on a wind farm 
constructed prior to approximately the year 2000 (maybe a bit later in 
the US) is inappropriate for estimating bird mortality based on modern 
turbine designs.

Whether by intent or because older studies are more common, opponents of 
wind power will have cited bird mortality data from studies done before 
2000 and, to make their point, are likely to focus on studies done on 
wind turbines erected in high exposure situations: e.g. in migratory 
pathways, at mountain passes, near nesting areas, and so on. Those are 
the numbers that get quoted at public hearings, published in the media, 
and that therefore underlie the collective consciousness about wind 
turbine hazard to birds. Not unlike what happens to people who 
constantly see fires crashes and shooting on the local news and come to 
think that what they are seeing is far more common than it really is, it 
all comes down to a risk communication problem.

Let's frame the threat with a simple risk management equation: Mortality 
equals hazard times exposure, or M= H * E. Individual hazard (H) is the 
probability of Tweety being smashed to bits if it flies into a wind 
farm. The last four paragraphs helped establish that H is getting 
smaller, not bigger. This means average bird mortality is also getting 
smaller and will likely continue to do so. We remain optimistic that 
additional technological means will be discovered to further reduce "H" 
and therefore "M." It might be as simple as avoiding any surfaces that 
would attract perching or nesting.

The exposure factor in the mortality equation ("E") is a bit more 
complex. "E" is obviously highest where birds migrate, breed, and feed 
in flocks near wind farms. There are very windy places where "E" is low 
all year: a dearth of birds. And there are certainly windy places where 
"E" is high only during a brief migratory period, or for a limited 
number of species which fly at a certain elevation.

Certainly the siting process needs to steer wind farms away from places 
where it can be shown that "E" is relatively high. Designers continue to 
work on lowering "H," while citizens, naturalists, municipalities with 
permitting or zoning authority, and scientists work to ensure that "E" 
is acceptably low. This is how it works. Once the turbines are up 
there's no chance to alter "H" for at least another 20 years. "E" can 
change year to year, however, depending on something as basic as which 
crops are planted nearby. For this aspect mitigation planning can be a 
part of permit approval.

Statements about "average" bird mortality ("M") do not well inform the 
debate over siting unless you get at the "H" and the "E" individually. 
By now it should be obvious that, like politics, all exposure is local. 
Citing an average "E" factor without some expert interpretation is not 
helpful. Having said that: here we go.

In the United States, cars and trucks wipe out millions of birds each 
year, while 100 million to 1 billion birds collide with windows. 
According to the 2001 National Wind Coordinating Committee study, "Avian 
Collisions with Wind Turbines: A Summary of Existing Studies and 
Comparisons to Other Sources of Avian Collision Mortality in the United 
States," these non-wind mortalities compare with 2.19 bird deaths per 
turbine per year. That's a long way from the sum mortality caused by the 
other sources.

For an excellent overview of all the major bird mortality categories we 
suggest you visit this site page 
<http://www.awea.org/faq/sagrillo/swbirds.html>maintained by the 
American Wind Energy Association