Hi brudenell,
Well hasn’t this been a most eye-opening project!
First I want to say, I went into this research with the same sense of
scepticism that I sense in your question. Although my 20-year old
degree in zoology sits officially unused, I’ve been a watcher of
animal behaviour all my life, and it made no sense to me that a bird
would fly into the blade of a wind turbine any more than it would fly
into the wind-blown branch of a tree. I mean come on; birds have an
incredible ability to manage movement and 3-dimensional space. Clear
windows aside, they generally don’t crash into things.
Also, I sometimes have my doubts about the rants of “humaniacs.” Sure
there are lots of reliable environmental and scientific organizations
out there doing real research and gathering real data. But there are
also a lot of over-zealous reactionaries who turn a couple of
bird-kills into a mountain of carcasses.
My goal in researching your question was to separate the wheat from
the chaff and find out what’s really going on here. The irony of the
whole issue, it turns out, is that it’s become a battle of
environmentalist against environmentalist. Here we have the folks who
are trying to promote clean power pitted against the folks who are
trying to save bird populations. Like the old television commercial
used to say, “But wait, you’re both right!”
So the question is, how big is this supposed mountain of carcases
really? And how does it compare to bird fatalities from other man-made
objects such as windows?
====================
SHORT ANSWER:
====================
Yes, there are many documented cases where birds have collided with
wind turbines. However, the frequency of such collisions is dependent
on things such as height of the turbine, length of the blades, speed
of the blades, the density of turbines on the wind farm, and most
importantly density of either local or migratory bird populationS.
Kill-counts per wind farm are generally numbered in the low to mid-
double digits annually.
Studies of Small Wind Energy Conversion Systems (residential use) show
that a single turbine has no increased effect on bird collisions over
any other stationary man-made object.
Birds also fly into glass, especially lighted glass and large panes on
high buildings or other structures. Far more birds are killed this way
than by wind turbines, with annual kill counts numbering in the
thousands per season for some single structures and estimated to total
over 100 million birds per year in North America alone.
=================
LONG ANSWER
=================
How many birds are killed by collisions with wind turbines and other
man-made structures?
Well, at it turns out, we’re in luck. Somebody has already done much
of the counting for us. In 1995 the California Energy Commission, in
response to public concern over the losses of birds due to collisions
with power lines, towers, wind turbines, and other structures, and
from electrocution by power lines, compiled an annotated bibliography
that specifically addressed the issue.
The bibliography contains 468 entries dating from 1876 to 1992. The
entries have been taken from journals or periodicals, conference
proceedings, government documents, private publications, utility
company reports, books, academic theses, and newspaper articles.
The commission read each article and specifically noted (where
possible) the number of birds reported killed, species, and cause of
death.
The entire bibliography is linked under RESOURCES below, but here are
three sample bibliographies from it, one a wind farm, one a
residential type wind conversion system, and one an example of birds
flying into glass ---
--------------------------------
8. Anderson, R.L., and J.A. Estep. 1988. Wind energy development in
California: impacts, mitigation, monitoring, and planning. California
Energy Commission, Sacramento. 12 pp.
Of 147 documented avian collision and electrocution incidents at
California wind energy facilities from 1985 to 1988, 101 have been
raptors. Of these, 34 were eagles and 58 were hawks. In the Altamont
Pass, an average of 11 eagle and 17 hawk incidents occurred annually.
Ninety-one percent of all documented avian mortality incidents
resulted in mortality. This mortality information identified the need
for further studies to better understand and resolve biological
effects of wind projects.
259. Lawrence, K.A. and C.L. Strojan. 1980. Environmental effects of
small wind energy conversion systems (SWECS). Prepared by the Solar
Energy Research Institute (now called National Renewable Energy
Laboratory), Golden, Colorado. Prepared for the U.S. Department of
Energy. 16 pp.
The authors conclude that the possibility of birds colliding with
rotors and towers of Small Wind Energy Conversion Systems (SWECS) is
"extremely small" based on the relatively low height of the rotors and
towers (an exception might be a very large wind machine sited on a
migratory route). Contributing factors noted are solidity of the rotor
design; airfoil design; number of organisms flying through the sweep
area; behavior of organisms within the sweep area, e.g., flight speed
or evasive flight patterns; weather conditions; and total structure
height.
56. *Bernard, R.F. 1966. Fall migration: western Great Lakes region.
Audubon Field Notes 20(1):45-46, 50-53.
At least 500 birds died by striking lighted windows and a neon sign
near Newberry, Michigan, on 26 September
-------------------------
The subject index of the bibliography lists the bibliography numbers
by COLLISION MORTALITY. For example –
Buildings, windows: 20, 31, 34, 55, 56, 79, 84, 86, 98, 108, 115,
156, 165, 195, 196, 212, 215, 218, 220, 224, 285, 312, 313, 344, 348,
352, 377, 437, 441, 443, 445, 451
Wind turbines: 3, 4, 8, 22, 59, 65, 80, 136, 191, 206, 207, 226, 227,
237, 259, 280, 287, 295, 297, 330, 331, 332, 334, 335, 346, 351, 366,
433, 461, 462, 463
Now this only gives us the number of references that refer to death by
each cause, not the actual numbers of birds. It wouldn’t be possible
to calculate exact numbers, without reading each and every article,
but it gives us an indication of how frequently such deaths are
reported. From this was can see is that collision with wind turbines
does in fact occur and is a frequent enough occurrence that it’s being
documented and studied carefully.
As an interesting aside; the number of references to collisions with
television and radio towers and power line and utility poles FAR
exceeds (10X) those for wind turbines. And each report, rather than
talking in quantities of tens or even hundreds, is referring to
kill-counts in the thousands per season.
For example: From 2 September to 10 October 1961, 5,097 birds were
collected at the Eau Claire, Wisconsin, TV tower. These were estimated
to be 10-20 percent of the actual total kill.
So, given that we now know that collision with wind turbines DOES
occur then what’s the story? Why (or how) are birds colliding with
wind turbines? (And by extension, why are they not colliding with
yours?) And how many birds has this really effected?
As far as the “why” goes, our bibliographies give us some clues. From
my reading of each of the annotations having to do with wind turbine
collisions, it is apparent that the following features of the wind
turbines are determinant in the frequency of bird impact:
• Height of the turbine
• Speed of the blades
• Structure of the tower
• Location of wind farm in relation to migratory routes and feeding
areas
• Density of turbines in a given area
In a statement made to congress, an expert witness, H. Hoffman,
stated:
“… The fact of the matter is that birds get killed when they roost on
the towers that support the wind machines, and their vision is so
acute that they see their prey and don't see the rotating blades which
are moving very fast, and so they take off after prey and fly through
the blades without even realizing the blades are there. So the real
problem is, how do you keep the birds from roosting on that wind
support structure before they ever go off after their prey?”
He was referring to the big culprit that has often been cited in
relation to bird-kills by wind turbines: The Altamont Pass Wind Farm
in California. Several large studies have been made of the bird
(primarily raptor) populations in that area and how they are affected
by this huge 7,000-industrial-turbine wind farm.
Altamont has everything going against it as far as protecting birds
goes. The density of the turbines (see the aerial photo below), the
structure of the towers which encourages raptors to perch, the height
of the turbines which interferes with the birds hunting, the density
of resident raptor (and prey) populations, and finally, the fact that
it lies right in the path of a migratory bird route. From the bird’s
perspective it couldn’t have been designed any worse.
Again, full citations and links are below, but I’ll highlight a few of
those studies here.
The National Renewable Energy Laboratory (NREL) sponsored a 4-year
study of golden eagle populations to be carried out by the Santa Cruz
Predatory Bird Research Group at the University of California, Santa
Cruz. The purpose of the study was to estimate the extent to which
turbine strikes and other hazards associated with wind energy
production at Altamont Pass alter the demographic potential of the
golden eagle population inhabiting the surrounding area.
Page 18 of this 43 page final report shows that there were 23
Radio-tagged Golden Eagle Casualties due to collision with turbine
blades documented between January 1994 and December 1997.
Another frequently cited study at Altamont (Anderson, R.L., and J.A.
Estep. 1988) showed that of 147 documented avian collision and
electrocution incidents from 1985 to 1988 –“ 101 have been raptors. Of
these, 34 were eagles and 58 were hawks. In the Altamont Pass, an
average of 11 eagle and 17 hawk incidents occurred annually.
Altamont pass may be an extreme, but studies at other experimental
wind farms have shown that the arrangement and density of turbines
certainly can contribute to bird death by collision.
For example, one Dutch study (Winkelman, J.E. 1992a) showed that avian
collision rates increased with an increase in the number of operating
turbines. Additionally, carcass location suggested that cluster
formations of turbines may reduce collision risk compared to straight
line or single row formation.
But, as bad as Altamont is, the total turbine collision death rate of
birds is still much lower than the 100 million birds per year that die
from collisions with glass in North America. It should also be noted
that window glass is not the only culprit. According to one
UNVERIFIABLE source:
“Boasting a bird kill per megawatt ten times greater that the champion
wind farm at Altamont Pass …Solar farms do it with mirrors. They birds
are attracted to them and collide with the shiny picture-like
heliostats that collect the sun’s rays.”
http://www.thetimesharebeat.com/wash/crossings41.htm
I’m not sure how much water that holds, but it’s going to have to be
saved for another question. I think we’ve researched this enough to
show that although large wind farms do present a certain risk to birds
in some circumstances, overall they have a much smaller effect on bird
population than glass windows and other man-made objects.
=================
RESOURCES
=================
Avian Collision and Electrocution: An Annotated Bibliography
California Energy Commission - October 1995
Publication Number: P700-95-001
http://www.energy.ca.gov/reports/avian_bibliography.html
SUBJECT INDEX
http://www.energy.ca.gov/reports/avian_bibliography.html#400
BIBLIOGRAPHIES FROM ABOVE CITED
Anderson, R.L., and J.A. Estep. 1988. Wind energy development in
California: Impacts, mitigation, monitoring, and planning. California
Energy Commission, Sacramento. 12 pp.
Winkelman, J.E. 1992a. The impact of the Sep wind park near
Oosterbierum (Fr.), the Netherlands, on birds, 1: collision victims.
DLO-Instituut voor Bos- en Natuuronderzoek. RIN-rapport 92/2. 4
volumes. (In Dutch; English summary.)
---------------------------------
Wildlife and Windmill
Windmills and Impact on Wildlife
http://www.windzone.mkeis.org/wildlife.htm
-------------------------
ALTAMONT PASS WIND FARM - AERIAL PHOTO
http://www.highton.com/pages/portfpages/altampassportf.html
A Population Study of Golden Eagles in the Altamont Pass Wind Resource
Area: Population Trend Analysis, 1994–1997
Predatory Bird Research Group; Long Marine Laboratory
University of California, Santa Cruz, California
http://www.nrel.gov/wind/26092.pdf
------------------------------
REPORT TO CONGRESS
ENERGY AND WATER DEVELOPMENT APPROPRIATIONS FOR 1998
WEDNESDAY, MARCH 19, 1997.
DEPARTMENT OF ENERGY
http://www.windzone.mkeis.org/wildlife.htm#Report%20to%20Congress
-------------------------------
American Zoo and Aquarium Association
Bird Collisions With Windows Fact Sheet
http://www.aza.org/ConEd/AvoidCollisions/
BIRD-WINDOW COLLISIONS ; DANIEL KLEM, JR
http://www.birdscreen.com/KlemCollisions1989.pdf
-------------------------------
Thanks so much for a thought-provoking question brudenell. It has
certainly been enlightening for me as I hope it’s been for you.
Please let me know if anything I’ve said isn’t clear or if any of the
links don’t work for you and I’ll be happy to clear things up.
Regards,
-K~
Search Terms:
Windmill bird kill
Wind turbine bird kill
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Wind turbine bird death rate
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