Creatures of the night

The long lives of bats counter their low reproductive rates but also increase their exposure to the other threat to their survival: wind turbines. While the degree to which bat populations can withstand higher mortality rates is unknown, Fenton believes that even small losses could drive their numbers down sharply.

Though studies have found that most wind farms cause fewer bird deaths than do other forms of land development, bats seem to be uniquely vulnerable to the turbines. Annual bat mortality at Ontario’s large wind farms ranges from four to 15 bats per turbine, according to the provincial Ministry of Natural Resources (MNR). U.S. wind farms have recorded anywhere from one to 50 fatalities annually per turbine. About 90 percent of the Ontario deaths occur during migration in late summer and early autumn, primarily among red, hoary and silver-haired bats, which spend the winter south of the province. Little brown bats, however, also migrate – up to 500 kilometres – to hibernation sites within
Ontario, as do eastern tri-coloured, small-footed and northern long-eared bats, all of which are killed by turbines.

The Wolfe Island wind farm, just south of Kingston, recorded Ontario’s highest bat fatality rate, as well as significant bird mortality, during testing in the second half of 2009. Searches found 180 dead bats, three-quarters of them long-distance migrants, beneath the farm’s 86 towering turbines. Factoring in projected rates of carcasses lost to scavengers or missed in thick vegetation raised the estimate to 1,270 deaths.

Jason Edworthy, director of community relations for TransAlta Corp., owner of the Wolfe Island operation, says the estimate seems high and may be due to unrefined methodology. “We only have six months of information. We’re going to increase the searcher efficiency testing and make sure we’re getting the most accurate numbers possible,” he says. “Our goal is to operate with as low an environmental impact as possible.”

Higher death rates – up to 30 bats per turbine annually – at a TransAlta wind farm that opened in 2004 near the foothills of the Rockies prodded the company to initiate several groundbreaking studies. University of Calgary researcher Erin Baerwald found that only about half the dead bats beneath the site’s 38 wind towers had actually been hit by the turbine blades. Few deaths at all were reported when the turbines were spinning in strong winds, when bats tend not to fly. At low wind speeds, however, bats seemed to be attracted to the towers. At least half the bats died after entering a spiralling low-pressure zone within three to four metres of the blades, which caused their lungs to expand and fatally hemorrhage.

Baerwald found that when turbine blades were slowed to almost a standstill on nights when the wind is low, up to 60 percent fewer bats were killed. TransAlta now runs the wind farm according to these parameters during the migration season, at a loss of only about one percent of its revenue. Pending further studies, the company has yet to follow suit on Wolfe Island.

Draft MNR guidelines introduced last March seem to at least partly apply the Alberta study and similar research. They require new wind farms to report all bat fatalities, from twice-weekly monitoring from May to September when bats are active, for three years after being built. If a site crosses a threshold of 10 bat fatalities per turbine per year, it must stop production at night when wind speeds are below 5.5 metres per second (almost 20 kilometres per hour), from July to September.

“Bat mortality decreases by 70 percent under that threshold,” says Fiona McGuiness, fish and wildlife program advisor for MNR’s Renewable Energy Program. She notes that the threshold is the first enacted anywhere in North America. “We have an opportunity now to get all of the data from wind farms and evaluate how effective the threshold and mitigation measures are,” she says.

But bat biologists believe, and Ontario Nature concurs, that the threshold is too high. Since the size of bat populations is unknown, says Fenton, the number of deaths cannot be put into context. “We know wind farms are hurting bats, but we don’t know whether 100,000 bats flew over, or 1,000 or 100,” he notes. “I think they should have a system of just turning off turbines when there is any bat traffic around, and they could do that by having bat detectors.” These are acoustic devices that pick up bat sonar – ultrasonic calls that bounce off objects and insect prey and back to the bats, enabling them to hunt and navigate in the dark.

Robert Barclay, who supervised Baerwald’s University of Calgary studies, adds that conservation measures should consider the cumulative effects of large wind farms, especially when they are regionally concentrated, as along lakeshores in Ontario. “You have the potential for bat populations moving through areas interacting with more than one wind farm,” he notes.

Critics also object to the emphasis in the guidelines on taking action only after the damage is done. Though nonbinding, MNR’s previous recommendations for wind farms, brought in three years ago, called for one to two years of pre-construction site monitoring using acoustic bat detectors. Now, the ministry says such monitoring isn’t effective in predicting post-construction bat mortality.

Recent research in both Canada and the United States contradicts that claim, counters Anne Bell, Ontario Nature’s senior director of conservation and education. Bell, who wrote Ontario Nature’s detailed response to MNR’s draft guidelines, stresses that her organization supports wind power, as long as it’s in a safe location (see, “Wind wars,” page 46). “I’m convinced it’s currently one of the best forms of energy we can go with. But let’s not be in such a rush to get turbines up that we’re regretting two years down the road where these wind farms have been sited,” she says. “We can understand that requiring pre-construction monitoring will slow things down, but we have to act responsibly.”

The one positive side effect of bats’ increasingly threatened existence is the research going into understanding their biology. “Because of wind farms and now white nose syndrome, there’s a lot of focus on bats across North America,” says Lesley Hale, a renewable energy science specialist with MNR’s Science and Information branch, who is leading searches for unidentified hibernation sites, mostly in southern Ontario. She notes that her branch spent almost $100,000 on two major bat studies last year. “That’s a much bigger investment than a few years ago.”

In one of last year’s studies, Fenton’s UWO graduate students at Long Point used radio transmitters to confirm for the first time that silver-haired bats migrate across Lake Erie between the latter part of August and mid-September. Species that migrate out of the province are particularly hard to study because they don’t roost in colonies – though silver-haired bats, which probably winter in the southeastern U.S., sometimes assemble in groups of around a dozen inside hollow trees or old woodpecker cavities. The hoary bat – Ontario’s largest species, with a wingspan of about 40 centimetres – and the red bat are even more elusive migrants, both swift, high fliers that roost in tree foliage.

UWO researchers are setting up acoustic monitoring stations to determine whether migrants follow large rivers and lakeshores or funnel into the Niagara Peninsula. Fenton says the plan is to establish as many monitoring sites, at about $3,000 apiece, as possible in sensitive areas. “Five years from now, we will have a lot of information we don’t have now,” predicts Fenton. In the meantime, he worries, the decisions Ontario makes about wind power may not err on the side of caution. “For someone who’s a bat freak and has been that way for a long time, I find this disappointing.”

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Tim Tiner is the co-author of a series of best-selling Ontario nature guide books.

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