The mortalities were largely silver-haired and hoary bats, neither of which is a species at risk. The deaths, which average 7.7 per turbine, came as surprise to both Vision Quest and local bat and wildlife experts. Although the mortality rate is much lower than the 38 bats killed per turbine during studies done at wind farms in West Virginia and Pennsylvania, where the issue first came to light in fall 2003, it is significantly higher than at other projects in the region. Vision Quest has recorded collision rates of 0.93 bats per turbine per year at its Castle River Wind Farm and 0.47 bats per turbine per year at its McBride Lake project.
"We didn't think there was as big a problem here, possibly because there aren't the number of bats here or because the topography the wind farms are on here is so different from the ridge top wind farms out east," says Robert Barclay, a professor at the University of Calgary's Department of Biological Sciences and a leading Canadian bat expert. "Then Summerview popped up and we realised the low numbers weren't universal, unfortunately, across wind farms on the prairies."
Why Summerview has experienced a higher rate of collisions is not clear, says Barclay. "We could make some guesses, but we really don't know because you go literally five or ten kilometres away to other wind farms and the numbers are really low."
The project is sited on flat, open prairie adjacent to the Oldman River and south of the Porcupine Hills, which the bats, because they are forest species, may be using as a place to roost during their migration. The turbines at Summerview, which are Vestas 1.8 MW units and among the largest installed in the region, may be a factor. "At the other farms they are smaller, older models and maybe the blades aren't up at the heights the bats are, whereas at Summerview they are," says Barclay. "The topography is also different. It may well be migratory bats are coming down along the edge of the Rocky Mountain foothills and encountering Summerview, whereas they are not moving en masse through other areas where wind farms are located. We just don't know."
Very little, in fact, is known about bat migratory behaviour in general, says Barclay. "We don't know whether they are using specific flyways like birds do and we need to avoid putting wind farms in those flyways, or whether they are migrating in a wave across much broader areas and only in certain places do wind farms and bats tend to come together."
Barclay does not think the potential for significant bat mortalities was something Vision Quest should have been aware of when was conducting site assessment at Summerview in 2003. "I'm not sure, given the state of understanding at the time, the wind farm would have been proposed and approved, that there was much they could have done. The problem just wasn't recognized."
Vision Quest, says executive director Jason Edworthy, hopes to get some answers during the course of planned research at the site. The company is providing funding assistance for a two year study by one of Barclay's students, who is investigating bat and wind turbine interaction for her Master's degree. It is also planning to bring in Western EcoSystems Technology, a US consulting firm that uses radar technology to track bat behaviour, to conduct research during the fall migration.
"Obviously one of our priorities is to find out what is going on," says Edworthy. "We have no idea whether this is an anomaly or not. But if we have an ongoing concern, then we need to know what can we do to mitigate it at Summerview and what can we learn from this so we can identify potential issues during baseline work at other sites."
Although the research planning is still underway, Edworthy expects it will look at issues like whether bats are using their echolocation abilities during migration or not, which could help explain why they collide with the turbines. Other questions, like what weather conditions and wind speeds promote migratory activity, what times of night bats migrate, and whether they are attracted by turbine sounds, lights or moving blades, are also key.
"One of the advantages we have is that we are not the first to have this concern. There are lots of people posing questions and coming up with hypotheses that we can then test," says Edworthy.
When the situation first became clear in the fall, the company took some preliminary steps to try and understand what was happening. Knowing that research has shown most collisions occur on nights when wind speeds are low, it locked the rotors on half the turbines to keep the blades from turning until the cut-in wind speed of 4.5 m/s was reached, and left the other half free to idle.
"What we found still needs to be analysed, but there is some indication that the machines that were on low wind shutdown had fewer collisions than those without. It wasn't across the board. We need to have some statistical work done to see if there is something there," Edworthy says. "But what it gave us was a hint that that might be a direction, and that helps us feed into future research."
Richard Quinlan of Alberta Fish and Wildlife says the fatalities at Summerview "raise red flags" for the government agency, which is responsible for wildlife management in the province. At the same time, he says, it is not clear how significant the deaths are to overall bat populations, which have proved difficult to survey. "We really don't know what the population size of these bat species is in Alberta or even continentally."
Quinlan is working with Alberta's wind industry to develop guidelines for siting and monitoring wind projects, which will include a set of monitoring protocols so developers can predict risk to bats prior to construction. "Like the other guidelines that would be a living document. As we learn more, I would expect there would probably be annual amendments."