The company that owns and operates the 86 wind turbines on Wolfe Island will take measures to try to reduce the number of raptors killed by the project.
A post-construction monitoring report released by TransAlta on Monday revealed that 10 raptor carcasses were recovered between Jan. 1 and June 30, 2010. A dozen were found between July 1 and Dec. 31, 2009.
While the annual raptor and vulture mortality rate of 0.12 raptors per megawatt – the Wolfe Island operation is 197.8 megawatts – is within the mortality range observed at other facilities in North America outside California (0 to 0.32 raptors per megawatt), it is higher than the notification threshold of 0.09 raptors/megawatt identified in the company’s followup plan.
In accordance with the plan, TransAlta and the Ministry of Natural Resources have initiated discussions regarding adaptive management. Raptor behav ioural studies are underway involving surveys during four peak mortality periods, and will continue across late summer and late fall 2010 and spring 2011.
“(The studies) will be conducted to better understand what the raptors are doing,” said Scott Hossie, environmental manager for TransAlta. “Is it flight patterns? Weather conditions? We’ll be gathering information to learn more about the potential effects and what needs to be done
“We’ll look to minimize the mortality rates where we can.”
In the period of the most recent study, seven red-tailed hawks, one osprey, one northern harrier and one turkey vulture comprised the group of 10 raptors killed by the turbine blades, which are 45 metres long. The 12 carcasses found last year included six turkey vultures and three red-tailed hawks.
The majority of the raptor and vulture fatalities appeared to be individuals migrating through the study area, the report said.
A consultant’s report estimates that 549 birds and 450 bats were killed between Jan. 1 and June 30, 2010. The estimates for the period from July 1 to Dec. 31, 2009, were 602 and 1,270, respectively.
“The numbers are in line in terms of other wind turbine sites in North America,” said Hossie, adding that different migration patterns and times were key factors in the lower rate of bird and bat deaths.
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. Combined with the results of the June to December 2009 period, the annual mortality is estimated at 13.39 birds per turbine.
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 followup plan.
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 to December 2009, the annual bat mortality rate is 19.99 bats per turbine.
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 followup plan.
Hossie said TransAlta will conduct research this year to evaluate practical measures to reduce the effects of wind turbines on bats on Wolfe Island. It will complete testing of potential mitigation measures – which may include programming the turbines so that they begin to rotate when wind speeds are higher – during the fall migration period in 2011
“Our intent is to have mortality rates as low as possible and we’ll do what we can to affect that,” said Hossie.
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