California's newest wind turbines may be killing more than 100,000 birds a year, according to a peer-reviewed study to be published in December. Those mortalities seem to climb the taller wind turbines get. And California wind turbines kill more wildlife per megawatt than identical turbines in other parts of the country.
What's more, though some have pointed to replacements of the old-style lattice structures holding up turbines with monopoles as a way of making wind turbines safer for birds -- by reducing the possibility that birds will try to perch on the turbine structures -- the study indicates that swapping lattice for monopole might not be the quick fix wind advocates had hoped for.
The study, conducted by Scott R. Loss and Peter P. Marra from the Smithsonian Conservation Biology Institute's Migratory Bird Center and U.S. Fish and Wildlife Service biologist Tom Will, appears in the December 2013 issue of the journal Biological Conservation.
The study was based on a survey of publicly available literature of bird mortalities at monopole-mounted wind turbines, and so its results are almost certain to be quite conservative: studies the trio included vary in the types of mortality surveys they include, and the group excluded individual studies that lumped turbine strike mortalities in with other causes of death. The three note that gaps in the information they used, which might affect the accuracy of their conclusions, could be filled if wind turbine owners were required to report their wildlife kills more stringently:
Despite numerous calls for an increase in the transparent reporting of study results and availability of reports to the public and scientists, collision data largely remains confidential and/or offline. Furthermore, reports that have been released to the public (e.g. on the internet) are often difficult to locate. We join previous authors in calling for increased transparency in data reporting. Requiring industry reports to be made publicly available would greatly improve understanding of wind energy impacts to wildlife.
But complete or not, the numbers the authors estimate for wildlife losses to newer, taller turbines are sobering. The study estimates that California's 13,851 monopole wind turbines (at the time of the study), which have a capacity of 5,796 megawatts of power output, kill between 56,095 and 161,335 birds each year -- with a mean figure of 108,715. That works out to an average of 7.85 annual wildlife kills per turbine (with those lower and upper estimates ranging from 4.05 to 11.65) and 18.76 annual deaths per megawatt of capacity (lower and upper estimates of 9.68 and 27.84, respectively).
Those figures are even more striking when the study puts them into a national context. California was one of four regions the authors designated for number crunching purposes, along with the East, the West (excluding California) and the Great Plains. Looking strictly at the mean figures provided, California monopole turbines' 108,715 estimated yearly wildlife kills are 46 percent of the 234,012 estimated for the nation as a whole, despite the fact that California's turbines make up only about a tenth of the country's wind generating capacity.
On a deaths-per-megawatt basis, California really stands out with a mean of 18.76 annual deaths per megawatt compared to 3.86 for the eastern region, 2.83 for the west, and 1.81 for the Great Plains. California's annual deaths per megawatt is so high that it pushes the national average above any of the three other regions, at 4.12 estimated annual bird deaths per megawatt of generating capacity.
And again, the authors excluded turbines on lattice mounts from their considerations, which means that the majority of turbines at the Altamont Pass Wind Resource Area, notorious for its high rate of bird deaths, isn't included in California's startling figures.
The authors also found that turbines with higher poles seem to kill more birds.
The new study's mortality estimates are significantly higher than some previous works, especially including those in a 2009 work by Benjamin Sovacool that explicitly dismissed wind-related wildlife mortality as a valid concern compared to other sources of power.
Loss and his colleagues anticipate Sovacool-styled objections even as they undermine his earlier wind-friendly work:
[O]ur results suggest that the amount of U.S. bird mortality caused by collisions at monopole wind turbines is non-trivial. Furthermore, the projected trend for a continued increase in turbine size coupled with our finding of greater bird collision mortality at taller turbines suggests that precaution must be taken to reduce adverse impacts to wildlife populations when making decisions about the type of wind turbines to install. Despite an apparent lower magnitude of bird mortality at wind turbines compared to other anthropogenic mortality sources (e.g., windows/buildings, communication towers, feral and pet cats), mortality at wind facilities should not be dismissed offhand.