<P> Sovacool estimated that in the United States wind turbines kill between 20,000 and 573,000 birds per year, and although he regards either figure is minimal compared to bird deaths from other causes . He uses the lower 20,000 figure in his study and table (see Causes of avian mortality table) to arrive at a direct mortality rate per unit of energy generated figure of 0.269 per GWh for wind power . Fossil - fueled power plants, which wind turbines generally require to make up for their weather dependent intermittency, kill almost 20 times as many birds per gigawatt hour (GWh) of electricity according to Sovacool . Bird deaths due to other human activities and cats total between 797 million and 5.29 billion per year in the U.S. Additionally, while many studies concentrate on the analysis of bird deaths, few have been conducted on the reductions of bird births, which are the additional consequences of the various pollution sources that wind power partially mitigates . </P> <P> Of the bird deaths Sovacool attributed to fossil - fuel power plants, 96 percent were due to the effects of climate change . While the study did not assess bat mortality due to various forms of energy, he considered it not unreasonable to assume a similar ratio of mortality . The Sovacool study has provoked controversy because of its treatment of data . In a series of replies, Sovacool acknowledged a number of large errors, particularly those that relate to his earlier "0.33 to 0.416" fatalities overestimate for the number of bird deaths per GWh of nuclear power, and cautioned that "the study already tells you the numbers are very rough estimates that need to be improved ." </P> <P> A 2013 meta - analysis by Smallwood identified a number of factors which result in serious under - reporting of bird and bat deaths by wind turbines . These include inefficient searches, inadequate search radius, and carcass removal by predators . To adjust the results of different studies, he applied correction factors from hundreds of carcass placement trials . His meta - analysis concluded that in 2012 in the United States, wind turbines resulted in the deaths of 888,000 bats and 573,000 birds, including 83,000 birds of prey . </P> <P> Also in 2013, a meta - analysis by Scott Loss and others in the journal Biological Conservation found that the likely mean number of birds killed annually in the U.S by monopole tower wind turbines was 234,000 . The authors acknowledged the larger number reported by Smallwood, but noted that Smallwood's meta - analysis did not distinguish between types of wind turbine towers . The monopole towers used almost exclusively for new wind installations have mortality rates that "increase with increasing height of monopole turbines", but as of yet, it remains to be determined if increasingly taller monopole towers result in lower mortality per GWh . </P>

What environmental concerns are associated with wind turbines