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Wind Turbines and Avians



 By Dolores Watson, GEO Wind Committee Volunteer


You have probably heard that wind turbines kill birds.  Unfortunately, some birds have been killed by flying into turbines, especially where little or no consideration was given to bird migration and/or existing populations in the immediate area.  But documented bird kills at wind turbines are small in comparison to kills at structures we see every day and never even consider as being a danger to our avian populations -- namely glass buildings and communications towers.


According to Leslie Evans Ogden, "The U.S. Fish and Wildlife Services (FWS) estimates that at least 4 million to 5 million birds are killed annually in communication tower collisions in the United States" Add this to the estimated 98 million birds killed annually by collisions with glass windows, especially those of tall office buildings, and it becomes clear that tall structures pose a very real threat to bird populations. (1)


On the other hand, a comprehensive review of communication tower kill literature published between 1995 and March 2000, commissioned by the U.S. FWS (which includes a section on wind turbine collisions), revealed that less than 100 avian fatalities involving wind turbines in the U.S. have been reported in that time period (excepting the installation at Altamont Pass).  The highly publicized bird kills at Altamont Pass in California are the only significant (large number) kills involving wind turbines reported at any installation to date. (2)


Communications Tower Collisions  (including TV/Radio and cell phone towers)


The website explains that two separate mechanisms seem to be in play causing bird kills at communications towers.  The first involves birds flying directly into the structures or guy wires in low visibility conditions, because they simply don?t see the obstacle in time to avoid the collision.  This can happen during the day when there is a heavy fog, or at night, and then theoretically more often at unlit towers.  But lighting the towers brings about the second mechanism. 


Communications towers that are lit at night for aviation safety may reduce the direct collisions under clear conditions, but when migrating birds lose their stellar cues on cloudy nights, they can be attracted to the lit towers.   Mortality occurs when they run into the structure, the guy wires, or even other birds as more and more birds are attracted to the same structure. (3)


Glass Building Collisions


The Fatal Light Awareness Program (FLAP), a Toronto-based group studying bird and building collisions since 1993, estimates that 100 million to 1 billion birds die each year due to collisions with human-built structures across North America alone.  You can visit the FLAP website at for more information.


Tall buildings that are lit at night pose a serious threat to migrating birds.  On cloudy nights the bird can be attracted to the lit buildings just like they are to the communications towers, with deadly results. 


During the day it is the reflective and transparent nature of glass that makes windows invisible killers.  Birds may see a tree reflected in a window, or a plant behind a window, but not see the window itself and will fly directly into it.  (4)


Reducing the Chance of Wind Turbine Collisions


Currently, companies seeking appropriate places to locate commercial wind turbines take the existing bird populations and migratory routes into account before they permanently site a facility.  Brian Kilkelley of Green Mountain Energy, reports no documented bird kills at the Garrett, PA facility since they went on-line in May 2000.


Please keep these documented facts in mind the next time you hear anyone proclaiming that wind turbines are dangerous to our bird populations.  Wind turbines can and do generate clean electricity with a minimum negative effect on the environment, including our bird populations.





  1. Ogden, Leslie Evans  "A Deadly Obstacle Course", Defenders of Wildlife, Fall 2000, pgs. 27-31.

  2. Kerlinger, Paul, Ph.D.  "Avian Mortality at Communications Towers, A Review of Recent Literature, Research and Methodology,"  March, 2000.  A study commissioned by the US Fish and Wildlife Service, Office of Migratory Bird Management.
  3. is a website responding to the ever increasing number of bird kills involving man-made structures.  It is their stated goal "to serve as an information resource on the tower kill problem and to promote cooperative solutions for mitigating the needless slaughter of millions of songbirds every year."  The website is not identified with an organizaitonal name.
  4. is the website produced by The Fatal Light Awareness Program (FLAP), a Toronto-based group studying bird and building collisions since 1993.