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Study of Marin’s McEvoy wind turbine: 3 dead bats, no dead birds

A wind turbine erected on a North Marin olive ranch amid pitched controversy – including concerns about an avian slaughter – has had “possibly nil” impact on birds, a three-year study concluded.

The comprehensive, 39-month study of bird mortality near the 148-foot McEvoy Ranch wind turbine turned up no evidence of any bird killed by the device, although three dead bats were found over the period.

“During the first 39 months of the McEvoy wind turbine operation, the observed avian mortality rate was zero – a strong indication that this particular wind turbine is not having an adverse impact on local bird populations,” the study reported.

“Though there is a small probability that some mortality events were undetected, the overall impact this single wind turbine has had on birds and bats during the study period appears to have been extremely small in the case of bats to possibly nil for birds,” according to Ryan DiGaudio and Geoffrey Geupel, experts from Point Blue Conservation Science, formerly known as Point Reyes Bird Observatory Conservation Science.

Their study was part of a monitoring program required by county supervisors who approved the turbine plan in 2007 amid protests from neighbors and environmentalists who cited vista and noise concerns and warned of a potential bird slaughter.

Terence Hallinan, representing neighbors, at the time urged new regulations for wind turbines to prevent commercial developments like the 5,400-wind turbine complex at Altamont from springing up in Marin. Thousands of birds are killed by the wind farm there.

“Without a plan in place, you’ll have developments like Altamont killing 100 raptors a day and bankrupting the county,” Hallinan told supervisors at the time. “We don’t want a debacle like that taking place in Marin.”

Representatives of Chronicle publishing heiress Nan McEvoy, now a Marin olive oil magnate, noted then that they worked through the permit process for nearly three years, reducing the height of the turbine by 40 percent, reducing power production to 250 kilowatts, changing site locations and making other moves to ease concerns.

A key opponent of the turbine was cheered by results of the study.

“That’s good news,” said Barbara Salzman, head of the Marin Audubon Society, after hearing about the study results. “It sounds good,” said Salzman, a foe of the project back in 2007. “I hope it’s accurate.”

The study issued in April involved systematic carcass searches two to three times weekly from July 2009 to October 2012. Some 187 searches were conducted primarily by trained ranch personnel whose efforts were judged 70 percent efficient through unannounced tests involving their ability to find bird carcasses planted on the site.

“According to relative size, 100 percent of large bird carcasses were found, 70 percent of medium bird caracasses were found, and 41 percent of small bird carcasses were found,” the study reported. At the same time, only five carcasses were removed by scavengers during efficiency tests that lasted for up to a week.

Salzman called use of ranch personnel “a little questionable” and said she will read the report to learn more about how the study was set up.

“You just can’t diminish three bats,” she said. “It would be much preferable not to have any mortality.” Wade Holland, the only county planning commissioner to support a bigger version of the McEvoy turbine, said he had no basis for drawing a conclusion about the study because he supported a bigger facility in a different location where the bird count might have been different.

McEvoy originally planned to build a 246-foot-tall wind turbine, powerful enough to power and heat the dozen or so buildings and olive oil processing plant on her 552-acre ranch. After neighbors and the Marin Planning Commission balked, McEvoy proposed a smaller structure, with a 98-foot tower and blades 40 feet long.

Built by Danish manufacturer Norwin, the 14-ton turbine is anchored to a knoll on the west side of the ranch off Petaluma-Point Reyes Road by 20-inch steel bolts driven into a 25-foot concrete foundation.