Amid all the talk about building more wind farms as an alternative form of energy production comes a finding by Canadian researchers that wind turbines are more dangerous to bats than they are to birds.

A team headed by the University of Calgary’s Erin Baerwald sought to discover why bats accounted for 60 percent of the winged animals found dead near wind farms in southern Alberta — a majority of which had no apparent injuries.

Their findings, published in Current Biology, were summarized in a University of Calgary news story:
 

"Because bats can detect objects with echolocation, they seldom collide with man-made structures," said PhD candidate and project leader Erin Baerwald. "An atmospheric-pressure drop at wind-turbine blades is an undetectable—and potentially unforeseeable—hazard for bats, thus partially explaining the large number of bat fatalities at these specific structures.”

"Given that bats are more susceptible to barotrauma than birds, and that bat fatalities at wind turbines far outnumber bird fatalities at most sites, wildlife fatalities at wind turbines are now a bat issue, not a bird issue."

The researchers said about 90 percent of the bats had suffered from internal hemorrhaging caused by a sudden drop in atmospheric pressure around the spinning turbines. About half showed any evidence of direct contact with the blades.

A ScienCentral YouTube story, "Wind Turbines Causing Dark Nights for Bats," compared the phenomenon to divers getting the "bends."

Calgary professor Robert Barclay said the fact that bats have a slow reproductive rate makes the wind farm factor significant — and could even bring bats to the brink of extinction.

"Slow reproductive rates can limit a population’s ability to recover from crashes and thereby increase the risk of endangerment or extinction," Barclay was quoted as saying, and he noted that migrating animals tend to be more vulnerable in the first place.

The UofC article continues:

All three species of migratory bats killed by wind turbines fly at night, eating thousands of insects—including many crop pests—per day as they go. Therefore, bat losses in one area could have very real effects on ecosystems miles away, along the bats’ migration routes.

Two species of nectar-feeding bats, the lesser long-nosed bat and the Mexican long-tongued bat, migrate north a thousand miles or more every spring from Mexico into Arizona, New Mexico and Texas, according to the U.S. Forest Service. The agency says both are listed as federally endangered species.

In New Mexico, there are 27 species of bats, with 19 listed as a Species of Concern, three species considered threatened and one species considered endangered, according to the state Energy, Minerals and Natural Resources Department.

Why should we care about bats?

Bats are beneficial as insect eaters. A bat eats half its body weight in insects each night and a colony can eat 150 tons of insects in one night.

But it’s also important to consider that bats are pollinators. This is especially important in light of the fact that so many of nature’s pollinators are in trouble, most notably the honeybees, as the New Mexico Independent has reported.

Bats take over pollination duties at night, particularly in the Southwest’s high desert.

The University of Calgary story suggests that modifying the speed of the turbines might alleviate the deaths, but the researchers stopped short of saying that would be a solution:

Baerwald said there is no obvious way to reduce the pressure drop at wind turbines without severely limiting their use. Because bats are more active when wind speeds are low, one strategy may be to increase the wind speed at which turbine blades begin to rotate during the bats’ fall migration period.

The study was initiated by the international energy company TransAlta after the company’s wind farm operators noticed bat carcasses below the turbines, and the company said it is working with the researchers to correct the problem.