Common Eco-Myth: Wind Turbines Kill Birds
by John Laumer, Philadelphia
April 6, 2006
http://www.treehugger.com/files/2006/04/common_misconce.php
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 maintained by the American Wind
Energy Association:
PUTTING WIND POWER’S EFFECT ON BIRDS IN PERSPECTIVE
by Mick Sagrillo
http://www.awea.org/faq/sagrillo/swbirds.html
Electricity generated from renewable energy resources is an
environmentally-preferred alternative to conventionally produced
electricity from fossil fuel and nuclear power plants. Many people
believe that wind turbines should be part of the solution to a
healthier environment, not part of the problem.
Over the past fifteen years, a number of reports have appeared in the
popular press about wind turbines killing birds. Some writers have
gone so far as to dub wind generators “raptor-matics” and “cuisinarts
of the sky”. Unfortunately, some of these articles have been used as
“evidence” to stop the construction of a wind generator in someone’s
back yard. The reports of dead birds create a dilemma. Do wind
generators really kill birds? If so, how serious is the problem?
A confused public oftentimes does not know what to believe. Many
people participate in the U.S.’s second largest past time, bird
watching. Other’s are truly concerned about the environment and what
they perceive as yet another assault on our fragile ecosystem.
Unwittingly, they rally behind the few ill-informed obstructionists
who have realized that the perception of bird mortality due to wind
turbines is a hot button issue, with the power to bring construction
to a halt.
Birds live a tenuous existence. There are any number of things that
can cause their individual deaths or collective demise. For example,
bird collisions with objects in nature are a rather common
occurrence, and young birds are quite clumsy when it comes to landing
on a perch after flight. As a result, about 30% of total first-year
bird deaths are attributed to natural collisions.
By far, the largest causes of mortality among birds include loss of
habitat due to human infringement, environmental despoliation, and
collisions with man-made objects. Since wind turbines fall into the
last category, it is worthwhile to examine other human causes of
avian deaths and compare these to mortality from wind turbines.
Death by�.
Utility transmission and distribution lines, the backbone of our
electrical power system, are responsible for 130 to 174 million bird
deaths a year in the U.S.1 Many of the affected birds are those with
large wingspans, including raptors and waterfowl. While attempting to
land on power lines and poles, birds are sometimes electrocuted when
their wings span between two hot wires. Many other birds are killed
as their flight paths intersect the power lines strung between poles
and towers. One report states that: “for some types of birds, power
line collisions appear to be a significant source of mortality.”2
Collisions with automobiles and trucks result in the deaths of
between 60 and 80 million birds annually in the U.S.3 As more
vehicles share the roadway, and our automotive society becomes more
pervasive, these numbers will only increase. Our dependence on oil
has taken its toll on birds too. Even the relatively high incidence
of bird kills at Altamont Pass (about 92 per year) pales in
comparison to the number of birds killed from the Exxon Valdez oil
spill in Alaska. In fact, according to author Paul Gipe, the Altamont
Pass wind farm would have to operate for 500 to 1000 years to
“achieve” the same mortality level as the Exxon Valdez event in 1989.
Tall building and residential house windows also claim their
share of birds. Some of the five million tall buildings in U.S.
cities have been documented as being a chronic mortality problem for
migrating birds. There are more than 100 million houses in the U.S.
House windows are more of a problem for birds in rural areas than in
cities or towns. While there are no required ongoing studies of bird
mortality due to buildings or house windows, the best estimates put
the toll due collisions with these structures at between 100 million
and a staggering 1 billion deaths annually.4
Lighted communication towers turn out to be one of the more
serious problems for birds, especially for migratory species that fly
at night. One study began its conclusion with, “It is apparent from
the analysis of the data that significant numbers of birds are dying
in collisions with communications towers, their guy wires, and
related structures.”5 Another report states, “The main environmental
problem we are watching out for with telecommunication towers are the
deaths of birds and bats.”6
This is not news, as bird collisions with lighted television and
radio towers have been documented for over 50 years. Some towers are
responsible for very high episodic fatalities. One television
transmitter tower in Eau Claire, WI, was responsible for the deaths
of over 1,000 birds on each of 24 consecutive nights. A “record
30,000 birds were estimated killed on one night” at this same tower.7
In Kansas, 10,000 birds were killed in one night by a
telecommunications tower.8 Numerous large bird kills, while not as
dramatic as the examples cited above, continue to occur across the
country at telecommunication tower sites.
The number of telecommunication towers in the U.S. currently
exceeds 77,000, and this number could easily double by 2010. The rush
to construction is being driven mainly by our use of cell phones, and
to a lesser extent by the impending switch to digital television and
radio. Current mortality estimates due to telecommunication towers
are 40 to 50 million birds per year.9 The proliferation of these
towers in the near future will only exacerbate this situation.
Agricultural pesticides are “conservatively estimated” to
directly kill 67 million birds per year.10 These numbers do not
account for avian mortality associated with other pesticide
applications, such as on golf courses. Nor do they take into
consideration secondary losses due to pesticide use as these toxic
chemicals travel up the food chain. This includes poisoning due to
birds ingesting sprayed insects, the intended target of the
pesticides.
Cats, both feral and housecats, also take their toll on birds. A
Wisconsin Department of Natural Resources (DNR) report states that,
“recent research suggests that rural free-ranging domestic cats in
Wisconsin may be killing between 8 and 217 million birds each year.
The most reasonable estimates indicate that 39 million birds are
killed in the state each year.”11
There are other studies on the impacts of jet engines, smoke
stacks, bridges, and any number of other human structures and
activities that threaten birds on a daily basis. Together, human
infrastructure and industrial activities are responsible for one to
four million bird deaths per day!
But what about wind turbines?
Commercial wind turbines
Since the mid-1980’s, a number of research organizations,
universities, and consultants have conducted studies on avian
mortality due to wind turbines. In the U.S., these studies were
prompted because of the relatively high number of raptors that were
found dead at the Altamont Pass Wind Farms near San Francisco.
After dozens of studies spanning nearly two decades, we now know that
the Altamont Pass situation is unusual in the U.S. The high raptor
mortality there was the result of a convergence of factors, some of
which were due to the bad siting in the local ecosystem while others
were due to the wind turbine and tower technology used at the time.
In fact, a very different situation exists not far away at the San
Gorgonio Pass Wind Farms near Palm Springs. A 1986 study found that
69 million birds flew though the San Gorgonio Pass during the Spring
and Fall migrations. During both migrating seasons, only 38 dead
birds were found during that typical year, representing only 0.00006%
of the migrating population.
A report recently prepared for the Bonneville Power Administration in
the Northwest U.S. states that “raptor mortality has been absent to
very low at all newer generation wind plants studied in the U.S. This
and other information regarding wind turbine design and wind
plant/wind turbine siting strongly suggests that the level of raptor
mortality observed at Altamont Pass is quite unique.”12
The National Wind Coordinating Committee (NWCC) completed a
comparison of wind farm avian mortality with bird mortality caused by
other man-made structures in the U.S.
The NWCC did not conduct its own study, but analyzed all of the
research done to date on various causes of avian mortality, including
commercial wind farm turbines. They report that “data collected
outside California indicate an average of 1.83 avian fatalities per
turbine (for all species combined), and 0.006 raptor fatalities per
turbine per year. Based on current projections of 3,500 operational
wind turbines in the US by the end of 2001, excluding California, the
total annual mortality was estimated at approximately 6,400 bird
fatalities per year for all species combined.”13
This report states that its intent is to “put avian mortality
associated with windpower development into perspective with other
significant sources of avian collision mortality across the United
States.”14 The NWCC reports that: “Based on current estimates,
windplant related avian collision fatalities probably represent from
0.01% to 0.02% (i.e., 1 out of every 5,000 to 10,000) of the annual
avian collision fatalities in the United States.”15 That is,
commercial wind turbines cause the direct deaths of only 0.01% to
0.02% of all of the birds killed by collisions with man-made
structures and activities in the U.S.
Back in Wisconsin
My home state of Wisconsin is a good example of current research. In
December of 2002, the report “Effects of Wind Turbines on Birds and
Bats in Northeast Wisconsin” was released. The study was completed by
Robert Howe and Amy Wolf of the University of Wisconsin-Green Bay,
and William Evans. Their study covered a two-year period between 1999
and 2001, in the area surrounding the 31 turbines operating in
Kewaunee County by Madison Gas & Electric (MG&E) and Wisconsin Public
Service (WPS) Corporation.
The report found that over the study period, 25 bird carcasses were
found at the sites. The report states that “the resulting mortality
rate of 1.29 birds/tower/year is close to the nationwide estimate of
2.19 birds/tower.16- The report further states, “While bird
collisions do occur (with commercial wind turbines) the impacts on
global populations appear to be relatively minor, especially in
comparison with other human-related causes of mortality such as
communications towers, collisions with buildings, and vehicles
collisions. This is especially true for small scale facilities like
the MG&E and WPS wind farms in Kewaunee County.”17
The report goes on to say, “previous studies suggest that the
frequency of avian collisions with wind turbines is low, and the
impact of wind power on bird populations today is negligible. Our
study provides little evidence to refute this claim.”18
So, while wind farms are responsible for the deaths of some birds,
when put into the perspective of other causes of avian mortality, the
impact is quite low. In other words, bird mortality at wind farms,
compared to other human-related causes of bird mortality, is
biologically and statistically insignificant. There is no evidence
that birds are routinely being battered out of the air by rotating
wind turbine blades as postulated by some in the popular press.
Home-sized wind systems
How does all of this impact the homeowner who wishes to secure a
building permit to install a wind generator and tower on his or her
property? They will likely still be quizzed by zoning officials or a
concerned public with little to go on but the sensational headlines
in the regional press. But while the press may or may not get the
facts right, peoples’ concerns are real, and need to be addressed
with factual information such as is presented here.
While there have been any number of studies done on bird mortality
caused by commercial wind installations, none have been done on the
impact of home-sized wind systems on birds. The reason? It is just
not an issue, especially when “big” wind’s impact on birds is
considered biologically insignificant.
When confronted with the question of why there were no studies done
on home-sized wind systems and birds, a Wisconsin Department of
Natural Resources person familiar with these issues responded, “it is
not even on the radar screen.” There has never been a report or
documentation of a home-sized wind turbine killing birds in
Wisconsin.
The Wisconsin Department of Natural Resources, or any other
government or research organization for that matter, just does not
have the financial resources to conduct a study just because a zoning
official requests it, especially given the lack of evidence
nationwide that any problem exists with home-sized turbines. Based on
our best available information, the relatively smaller blades and
short tower heights of residential wind energy systems do not present
a threat to birds.
See also: Bats and Wind Turbines
Notes:
1. National Wind Coordinating Committee Avian Collisions with Wind
Turbines: A Summary of Existing Studies and Comparisons to Other
Sources of Avian Collision Mortality in the United States (NWCC), p.
10.
2. NWCC, p. 10.
3. NWCC, p. 8.
4. Tower Kill p. 2.
5. Communication Towers: A Deadly Hazard To Birds p. 19.
6. Battered By Airwaves p. 6.
7. Battered By Airwaves p. 4.
8. Communication Tower Guidelines Could Protect Migrating Birds p. 2.
9. NWCC p. 12.
10. The Environmental and Economic Costs of Pesticide Use p. 1.
11. Cats and Wildlife: A Conservation Dilemma p. 2.
12. Synthesis and Comparison of Baseline Avian and Bat Use, Raptor
Nesting and Mortality information from Proposed and Existing Wind
Developments p. 7.
13. NWCC p. 2.
14. NWCC p. 1.
15. NWCC p. 2.
16. Effects of Wind Turbines on Birds and Bats in Northeast Wisconsin
p. 68.
17. Effects of Wind Turbines on Birds and Bats in Northeast Wisconsin
p. 75.
18. Effects of Wind Turbines on Birds and Bats in Northeast Wisconsin
p. 67.
References:
Avian Collisions with Wind Turbines: A Summary of Existing Studies
and Comparisons to Other Sources of Avian Collision Mortality in the
United States; National Wind
Coordinating Committee; West, Inc.; August, 2001
Battered By Airwaves; Wendy K. Weisenel; Wisconsin Department of
Natural Resources; October, 2002.
Cats and Wildlife: A Conservation Dilemma; John S. Coleman, Stanley
A. Temple, and Scott R. Craven; University of Wisconsin-Extension;
1997.
Communication Towers: A Deadly Hazard To Birds; Gavin G. Shire, Karen
Brown, and Gerald Winegrad; American Bird Conservancy; Jume, 2000.
Communication Tower Guidelines Could Protect Migrating Birds; Cat
Laazaroff; Environmental News Service; 2002.
Effects of Wind Turbines on Birds and Bats in Northeast Wisconsin;
Robert W. Howe, William Evans, and Amy T. Wolf; November, 2002.
Synthesis and Comparison of Baseline Avian and Bat Use, Raptor
Nesting and Mortality information from Proposed and Existing Wind
Developments; West, Inc.; December, 2002
The Environmental and Economic Costs of Pesticide; David Pimentel and
H. Acquay; Bioscience; November, 1992.
Tower Kill; Joe Eaton; Earth Island Journal; Winter, 2003.
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