[permaculture] Common Eco-Myth: Wind Turbines Kill Birds
saor at ycbtal.net
Sat Apr 8 11:18:55 EDT 2006
Common Eco-Myth: Wind Turbines Kill Birds
April 6, 2006 07:01 AM - John Laumer, Philadelphia
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
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
Recapping: small blades, low surface area, lots of dead birds possible;
very big blades, with large surface area exposed to wind, very few dead
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
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
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
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