Wind Turbine Bird Threat Overstated, Study Suggests

The growth of wind power, if undertaken with reasonable care, should pose no risk to any particular bird species in Canada, according to a new peer-reviewed study. The study also suggests that highly publicized bird mortality figures out of the U.S. and Europe could be on the high side.

“Canadian Estimate of Bird Mortality Due to Collisions and Direct Habitat Loss Associated with Wind Turbine Developments” [PDF] was one of several studies undertaken as part of special issue of the journal Avian Conservation & Ecology that focused on the impact of human activities on the mortality of birds in Canada.

wind bird conflict u.s. wind development guidelines

image via Shutterstock

The researchers did find that, on average, a wind turbine in Canada results in 8.2 bird deaths per year, and they estimated that a 10-fold increase in installed wind capacity in the next 10-15 years “could lead to direct mortality of approximately 233,000 birds/year, and displacement of 57,000 pairs” resulting from habitat loss.

But the researchers put those numbers in perspective:

[T]hese values are likely much lower than those from collisions with some other anthropogenic sources such as windows, vehicles, or towers, or habitat loss due to many other forms of development. Species composition data suggest that < 0.2% of the population of any species is currently affected by mortality or displacement from wind turbine development. Therefore, population level impacts are unlikely, provided that highly sensitive or rare habitats, as well as concentration areas for species at risk, are avoided.

One of the most interesting aspects of the study was that mortality figure of 8.2 birds per year per turbine – 8.2 ± 1.4 birds (95% C.I.), to be precise. The researchers said this was a higher estimate than had been found in other research into turbine-related bird mortality in Canada, “due mainly to incorporation of two additional correction factors: the proportion of birds likely to fall outside a 50 m search radius, and the proportion of birds killed at other times of year.”

Yet even with these expanded correction factors, the 8.2 figure is still notably lower than a bird mortality estimate for the U.S. that is frequently cited by wind power critics, from Albert Manville of the U.S. Fish & Wildlife Service (we discussed that study a bit here).

Manville (2009) suggested that annual bird mortality from wind power projects in the United States was 440,000 birds, which equals about 19 birds per turbine based on an estimated 23,000 turbines at the time. However, he did not provide any details on how this estimate was derived.

The Canadian researchers also arrived at a mortality rate far lower than the recent, controversial K. Shawn Smallwood paper. The Canadian researchers suggested there were a number of reasons to believe Smallwood’s numbers were too high:

For example, he used larger corrections for birds falling outside a 50 m radius; by assuming a logistic distribution of carcasses, he concluded that carcasses could fall up to 156 m away from an 80 m turbine, though this is farther than Hull and Muir (2010) suggested is likely. Furthermore, his analysis assumes that mortality is proportional to the rated capacity of the turbines, but particularly for newer turbines this seems unlikely; for example, there is only a 19% increase in the blade swept area between a 1.5 and 3.0 MW turbine.

The study was also skeptical of an often-cited Spanish estimate of 300-1,000 birds per turbine.

Their very high mortality estimates were based on assumptions that searcher efficiency was extremely low, scavenger rates were very high, and large numbers of carcasses fell outside the search areas. However, no evidence was presented to support those assumptions, and it is quite possible that mortality rates were not actually any higher than those in Canada.

If you’re wondering which things were determined to be the biggest bird killers in the other Avian Conservation & Ecology studies, this press release from the American Bird Conservancy (a frequent wind industry critic) tells the story well. Key passage: “[T]he median estimate of cat-caused mortality – almost 200 million bird deaths per year – was about six times greater than the next leading mortality estimate of about 32 million attributed to car collisions. The third-leading cause was collisions with buildings or homes, with a rate of about 22 million bird deaths per year.”

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

  • alpha2actual

    I find the domestic cat argument specious. Domestic cats don’t kill raptors even my 18 pound Maine Coon would not mess with an eagle. Prior to wind turbine farms cats, cars, power lines, buildings etc cumulatively kill X avians. Turbines, concentrated and passive solar kill Y. X+Y= impact on avian populations. The Y contains raptors, large passerines, large migratory species. The commercial wind turbine adverse impact on bat populations should be noted. Bats are natures pesticide, it has been calculated that one bat is as effective as $74 of chemical pesticide over the course of a growing season. The fact that wind turbines kill bats has been observed for decades but it has been only recently that wind farm induced fatalities on autumn migratory bat population have been studied. Bats are attracted to wind turbines for several reasons, motion, harmonics, and tracking insects which are also attracted by the turbines. The problem is that the bat doesn’t have to make contact with the blade to be a fatality. The change in air pressure is enough to collapse the lungs of the bat a condition known as Barotrauma. This is a particularly dangerous time for bats particularly for some endangered species because of White Nose Syndrome discovered in 2006 which is rapidly spreading. This fungus is 95% fatal and has killed between 5.7 million to 6.7 bats.

  • Steven Lyle Jordan

    With the ongoing R&D into turbine appearance (colors, paints, lights, etc), we can only hope that avian death rates will drop significantly over time. That R&D should be top priority right now.

  • SolarPal

    I appreciate that the other factors of bird mortality are also mentioned and that there are numbers given to put wind turbine bird deaths in perspective. Also, how about the numbers of birds and multitudes of wildlife harmed by gas and petroleum. What about oil derricks and refineries and petroleum product spills? It I don’t think wind turbines could ever reach the numbers of deaths and injuries caused by spills. I imagine someone could compile data showing this wildlife destruction.

    • Pete Danko

      You raise an excellent point, SolarPal. One of the studies did attempt to look at the impact from gas and petroleum exploration and extraction in the Western Canadian Sedimentary Basin. It’s tough to nail down a single number, but here’s what the researchers found:

      The estimated number of nests disturbed annually by all oil and gas sectors combined ranged between 11,840 – 60,380. Interannual variation in exploration and extraction, and uncertainty in nest densities and the proportion of the disturbances occurring during the breeding season contributed to the variation. Accounting for natural mortality suggests an estimated loss of 10,200 – 41,150 (range) potential recruits into the migratory bird population in a subsequent year. Although nest destruction is only one small component of the potential impacts of the oil and gas industry upon avian populations, these estimates establish a baseline for comparison with other sources of human-caused avian mortality. Models are now needed to compare nest losses against the legacy effects of oil and gas sector habitat disturbances and associated cumulative effects so that mitigation efforts can be prioritized.

      The full study is here: