Each wind turbine in Canada kills an average of 15.5 bats per year, adding up to a death toll that could someday threaten populations, according to new research. In Canada's first comprehensive analysis of wind farm casualties, researchers found that turbines were killing about 47,000 bats per year in 2013. That number will only rise as Canada's investment in wind energy increases.
"We have about 50 percent more turbines now, so, as of 2016, somewhere around 70,000 bats are being killed in Canada per year," said Ryan Zimmerling, a wildlife biologist with the Canadian Wildlife Service and first author of a recent study in the Journal of Wildlife Management. "It is possible that those levels of mortality, if they're not already causing impacts to some species now, could be causing impacts into the future."
Wind energy companies in Canada are required to monitor bat mortality at newly built wind farms, regularly searching the area under turbines for carcasses. The companies report these data as part of post-construction monitoring, but until now, no one had combined them into a single nation-wide analysis. To see the big picture, Zimmerling and his colleagues analyzed carcass counts from 64 wind farms in nine provinces, using statistical corrections to estimate how many carcasses the surveyors missed.
The results varied widely by region. Hardly any bats died in New Brunswick and Manitoba, both because those provinces don't have many wind farms and because each turbine there killed fewer than one bat per year. In contrast, Ontario's 1,270 turbines each killed an average of 24.5 bats per year, accounting for two thirds of the whole country's death count. It's not clear why turbines are more dangerous in certain places, though the answer could have something to do with bat migration routes, says Zimmerling.
Multiple studies have found that migratory species are especially vulnerable to wind farms, and the new study showed that Canada's bats are no exception. The species killed most often were the three that migrate long distances: hoary bats (Lasiurus cinereus), silver-haired bats (Lasionycteris noctivagans) and Eastern red bats (Lasiurus borealis). Researchers aren't sure why migrating species are more at risk, but they have a few guesses, says Zimmerling. Migrating bats fly at higher altitudes, which could put them at the same height as the turbine blades. Additionally, the animals might mistake turbines for the tall trees they like to roost in.
The seven hibernating species in the study were less frequent victims, accounting for fewer than a quarter of carcasses. But even low mortality rates could cause problems for these species, because they are the ones suffering from the disease known as white-nose syndrome. White-nose fungus (Pseudogymnoascus destructans) grows on bats while they hibernate, and it has decimated species such as the little brown bat (Myotis lucifugus). The researchers estimate that up to 1.4 percent of the remaining little brown bats in eastern Canada are killed by turbines each year.
That estimate rests on several assumptions, and researchers need more data on bat population sizes to really understand the impact of wind farms, says Zimmerling. Indeed, little brown bats were one of only two species in the study for which any population estimates existed.
"We feel fairly confident that we have a good handle on how many bats are going to be killed in the future," he said. "That missing link is: Is it having an impact right now, or is it likely to have an impact into the future? And without population data for bats, we just don't have a clue."