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Volume 25, Issue 3, Fall 2007

Prairie Winds

Migrating bats & wind energy in Canada

By Erin Baerwald

Migratory tree bats – hoary, silver-haired and eastern red bats – are among the most spectacular and widespread bats in North America, yet we know very little about them and almost nothing of their migratory behavior. Studying these bats (and their encounters with wind-energy turbines) on the Canadian prairies might seem a little crazy. The featureless landscape with few trees and scarce water is hardly prime bat habitat. The winds that blow strongly and incessantly make catching bats almost impossible. And when I began my research two years ago, high bat kills at wind turbines seemed mostly limited to facilities built on forested ridgetops in eastern North America.

Nonetheless, the southwestern Alberta prairie is where I chose to study migratory bats and wind energy. Little did I suspect that meant I would become a diurnal bat biologist, slogging through waist-high wheat in 104-degree F (40-degree C) heat or hailstorms or snow. Knowing that we were adding to our understanding of the basic biology of migratory tree bats while perhaps also helping to reduce the wind-energy risks to bats kept me and my team going through the unpredictable conditions of the bat-migration season on the prairie.

I began my research at the Summerview Wind Farm in fall 2005, shortly after environmental consultants for the owner, Transalta Wind, began reporting large numbers of bat fatalities at the new facility. They found 532 hoary and silver-haired bats under Summerview’s 39 turbines in 2005. That fatality rate of 14 bats per turbine per year was unprecedented in Alberta – other wind-energy installations in the region had fatality rates of less than one bat per turbine-year. [These rates are not corrected for searcher efficiency and carcass removal by predators, which would significantly increase the totals.]

It also came as a huge surprise to bat biologists and the wind-energy industry. High bat-fatality rates had been recorded at the Mountaineer Wind Energy Center in West Virginia, and reports were beginning to trickle in from other wind-energy installations (see BATS, Fall 2005 & Fall 2006). But the flatland prairie at Summerview had little in common with the eastern ridgetops on the other side of the continent. These bat fatalities in Canada suggested the issue was much broader than anticipated.

Some patterns were emerging, however. At North American locations studied thus far, most bat fatalities at wind-energy facilities have occurred in late summer and early fall and mostly involve three migratory species: hoary bats (Lasiurus cinereus), eastern red bats (Lasiurus borealis), and silver-haired bats (Lasionycteris noctivagans). This pattern appeared to hold true at Summerview, where more than 90 percent of fatalities occurred between July and September and involved hoary and silver-haired bats.

I had already been in consultation with Transalta, and we took the opportunity to collaborate with other industry partners (Suncor Energy Inc., Alberta Wind Energy Corporation and ENMAX Corporation) to investigate the causes of bat fatalities and learn more about the basic biology of migratory bats in Alberta. My work this year is supported in part by a BCI Student Research Scholarship.

Among research goals, I am determining how weather and time of night might influence migrations and fatalities; how migratory activity varies across the landscape; and the effectiveness of acoustic monitoring in predicting the risk to bats at proposed wind-energy sites. Field research and data analysis continue, but my initial results include hints that might help reduce bat kills at some wind farms.

In my first field season in 2006, I spent May through September at three existing wind farms and three other sites where wind facilities are proposed in southern Alberta. Summerview was my primary study site. From mid-July to the end of September, my field assistants and I conducted daily searches around 10 of Summerview’s 39 turbines, carefully looking for dead or injured bats. We searched the other 29 turbines once a week. We also used Anabat detectors to estimate the activity of different bat species as they passed through the wind-energy installations each night.

We counted 619 dead bats around the turbines in 2006. Most (62 percent) were hoary bats, and 34 percent were silver-haired bats. The eastern red bat, frequently killed at wind farms in eastern North America, is considered rare in Alberta. Yet we found the carcasses of five of them under the turbines.

Previous studies had suggested that only female hoary bats migrate into northwestern Canada. We, however, found more male hoary bats than females. We also documented that both males and females, and juveniles as well adults, are vulnerable to being hit by turbine blades.

A curious feature of bat fatalities at wind-energy sites studied across North America is that they occur mainly in the fall, as bats migrate south for the winter, but rarely in the spring. Somehow, the bats avoid wind turbines on their northward migration. That clearly is the case in Alberta: Fatalities begin in mid to late July, peak in August and taper off by the end of September.

We also found that different species and sexes migrated at different times. In July, we found mainly male hoary bats. Then came the females and their young. Mixed age and gender groups of silver-haired bats accounted for most of the fatalities in September.

It seems puzzling that bats are struck by structures as large as turbine blades, yet they can use their echolocation system to detect a fruit fly. Some biologists have suggested that bats may simply turn echolocation off during migration. My results suggest this is not the case.

With the help of Transalta personnel who climbed up inside the 213-foot-high (65-meter) turbine towers, I mounted bat detectors on the hubs of several wind turbines and on weather-monitoring towers. Echolocation calls of migratory hoary, silver-haired and red bats were detected.

Detectors on the ground, however, mostly recorded the echolocation calls of the area’s (non-migratory) resident bats, such as little brown myotis (Myotis lucifugus) and big brown bats (Eptesicus fuscus), that feed relatively close to the ground and away from the spinning turbine blades. Up high, I recorded few bats of these species, but many more migratory bats. This suggests that ground-level bat detectors may not accurately assess potential risks to migratory bats at proposed wind-energy sites. Monitoring at blade level, which is far more difficult, may be required.

My data from across southern Alberta also suggest that the number of migrating bats varies significantly from site to site. This may help explain why some wind farms have higher bat-fatality rates than others. If there are strong correlations between migration activity levels and fatality rates, this could help in future site selection.

My initial results are less clear about factors that might influence the timing of bat migrations, a little-understood subject. Particularly high activity was recorded on some nights at some locations, but I found no clear pattern of weather variables associated with these migratory “events.” Perhaps the data we are collecting this year will help us tease apart some relevant factors.

Wind energy and other alternative sources of renewable energy are important components of the energy mix and of efforts to reduce global climate change. We must remember, however, that almost everything we do – including renewable energy – has an impact. But with the collaboration of the Canadian wind-energy industry, we are learning about wind energy’s impact on bats so that we can minimize those risks. Given the rate of new construction all across North America, studies such as this are urgently needed.


ERIN BAERWALD is a graduate student at the University of Calgary. This research is part of her work toward a Master of Science in Biology.

ERIN BAERWALD is a graduate student at the University of Calgary. This research is part of her work toward a Master of Science in Biology.

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