There were fewer birds and bats killed by wind turbines on Wolfe Island in the first half of 2010 than during the previous six months, but the number of dead raptors is cause for concern, says a bird expert.
During the period between Jan. 1 and June 30 of last year, 10 raptor carcasses were recovered, compared to 12 between July 1 and Dec. 31, 2009.
Seven red-tailed hawks, one osprey, one northern harrier and one turkey vulture comprised the group of 10 raptors killed by the giant blades.
“We were hoping (12) was an aberration, but it seems to be steady,” said Erwin Batalla, chairman of the nature reserve committee of the Kingston Field Naturalists. “The raptors are the most concern. It’s probably one of the higher raptor mortality rates at a wind turbine.
“Wolfe Island probably doesn’t have many (raptors). One osprey could be 10% of the (species’) population.”
The seven red-tailed hawks, said Batalla, could represent as much as 35% of the species on the island.
The island’s raptor population could dwindle over time, he said.
“There’s not a lot of nesting raptors on Wolfe Island, but (the mortality rate) might be 10% per year,” said Batalla. “Locally, one day they might not be there any more.”
The mortality figures were released Monday by TransAlta, which owns and operates the 86-turbine, 197.8-megawatt facility. A TransAlta environmental services manager was unavailable for comment Tuesday.
A consultant’s report estimates that 549 birds and 450 bats were killed between Jan. 1 and June 30, 2010. The estimates for the previous six months were 602 and 1,270, respectively.
According to the latest report, 66 carcasses of 28 bird species were collected during the reporting period. The estimated mortality for all birds is 6.39 per turbine (the turbine towers are 80 metres high and each turbine is 45 metres long.). Combined with the results of the June-December 2009 period, the annual mortality is estimated at 13.39 birds per turbine.
The species killed included a couple dozen swallows and martins, one chimney swift and one bobolink – both of which are considered threatened species.
The birds’ death rate was distributed uniformly through the spring (April, May and early June). There were fewer in February and March, and none reported in January.
Batalla offered a couple of theories on why the bird mortality figures were down.
“Birds don’t follow the same migratory path in spring as in fall,” he said, adding that weather can also be a factor.
“Smaller birds fly higher when it’s a clear day and lower when there’s cloud cover.”
The annual mortality rate of 5.82 birds per megawatt is far below the adaptive management threshold of 11.7 birds per megawatt identified in Trans -Alta’s post-construction follow-up plan.
According to Environment Canada, the annual bird mortality rate is within the range of other wind farms in Canada and the U.S., but it is the fifth-or sixth-highest mortality level reported from 45 wind farms in North America.
When mortality is calculated on a per megawatt basis, said Environment Canada, the Wolfe Island numbers are comparable to levels reported at other North American wind projects.
The government agency said that while the mortality rates may be high, they are not unexpected given that the area is important for breeding, wintering and staging birds.
The report also states that 34 carcasses of three bat species – including 28 silver-haired bats – were collected during the reporting period. The estimated mortality rate is 5.23 bats per turbine. Combined with the results from July-December 2009, the annual bat mortality rate is 19.99 bats per turbine.
Batalla admitted he doesn’t know a lot about bats, but he said some species hibernate during winter while others migrate south. Those could be factors in the sharp drop in the mortality rate, he suggested.
The annual mortality rate of 8.69 bats per megawatt is at the median of the mortality range observed at other facilities in North America, which range from 0 to 39 bats per megawatt. The rate is below the threshold of 12.5 bats per megawatt as identified in TransAlta’s follow-up plan.
TransAlta says it will conduct research this year to evaluate practical measures to reduce the effects of operating wind turbines on bats at the wind plant. It will complete testing of potential mitigation measures during the fall migration period in 2011 to determine the feasibility and effectiveness of implementing such mitigation measures at Wolfe Island.
The estimate of 602 bird deaths in the second report was based on a total of 100 bird carcasses found beneath the turbines during the first half of 2009; the 1,270 bat deaths estimate was based on 180 actual bat carcasses.
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