Bird and Bat Mortality

Bird and Bat kills have been a source of controversy since the inception of large scale wind power. While wind turbines account for a small percentage of bird kills annually, the issue is popular for wind farm opponents. The belief that birds would fly into the spinning turbines and die seemed to be proven at Altamont Pass in California, one of the earliest wind farms in the US. Altamont Pass is just outside of San Francisco and has seen wind turbines built there continuously since the early 1980’s. Over the years, a number of bird kills have been reported with numbers of raptor kills estimated at 880-1,330 annually with death rates ranging from 0.02 to 0.05 birds per turbine per year (Thelander et al. 2003). This is particularly distressing since many raptors are listed as endangered. However, as a BioResource Consultants report states, features of Altamont make it particularly susceptible to bird kills. The area itself is habitat for a number of raptor species. A number of the turbines currently operating at the sight are old technology with shorter towers and faster blades (correlated to bird kills). Raptors experience high mortality in these areas because they tend to perch at high points and swoop down on top of there prey. Not only does this put them in contact with the short faster turbines, but they are concentrating on the ground and do not see the turbines. This issue is further worsened by the activities of raptor prey which tend to burrow in areas created by the construction of the turbines.

Information gathered from areas such as Altamont has helped the wind industry understand how bird behavior effects their mortality around wind turbines. Areas where birds nest or hunt are particularly susceptible to kills due to the animals proximity to the turbines and/or its awareness of the surroundings. Actions to reduce prey habitat can help to reduce raptor kills in these areas.

In addition to raptor kills, concerns have been raised about sights in close proximity to migrating birds, such as marshes. The Environmental Impact Statement issued for the Horicon Marsh sight in Minnesota expresses concern for the large number of migrating birds in the area as well as for “weak” flying birds such as Whooping Cranes. It states that birds using the marsh during migration may come in contact with the turbines as they climb to altitude during take-off, especially for nocturnal bird flight.

More recently bat kills have become a source of concern for wind farm developers and environmentalists alike. The Backbone area in northern West Virginia has seen an alarming number of kills. In particular the Mountaineer Wind Energy Center owned by Florida Power and Light (a leading wind farm developer) has experienced an alarming number of kills since coming on line in mid 2003 and is currently studying ways to abate the issue. Given bats’ ability to “see” at night, many wonder what it is that causes the bats to hit the blades. A study done on the Buffalo Ridge Sight in Minnesota indicated that migrating bats were more susceptible to collisions than local bats potentially due to “turning off’ their radar as they migrate and cited not relationship between bat activity and bat collisions at turbines.

Bat collisions are being seen at an alarming rate at some wind farms and this issue requires additional study to determine ways to mitigate the problem.

Article on Bat Kills	http://www.safewind.info/faq_bats.htm
Article on Bat Kills	http://www.batcon.org/newsletter/enews-0804/article1.html
Bat Conservation International	http://www.batcon.org/
Report on Bat and Bird Kills	http://www.batcon.org/wind/BPAAvian-BatStudy12-2002.pdf
NREL Bird Kill Study	http://www.nrel.gov/docs/fy02osti/28591.pdf
AWEA Bird Kill Study	http://www.awea.org/pubs/documents/WEBBProceedings9.14.04[Final].pdf
Environmental Summary from Cape Wind	http://www.capewind.org/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=38&page=1
Article on Bird Kills at Horicon Marsh	http://www.wisinfo.com/thereporter/news/archive/local_20538985.shtml
Other Bird Kill	http://www.currykerlinger.com/birds.htm

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