Wind turbines pose danger to migratory bats: study

Yahoo News 26 Aug 08;

Their deaths could also affect ecosystems on the bats' migration routes as they eat thousands of insects, including many crop pests, every day

Wind turbines pose a greater danger to bats than birds as the power generators produce a sudden drop in air pressure that causes the nocturnal animal's lungs to burst, a study has found.

While the turbines' blades may endanger birds, Canadian researchers found that 90 percent of bats found dead at wind farms had suffered internal hemorrhaging caused by the drop in air pressure, a condition known as barotrauma.

Only about half of the migratory bats showed any evidence of direct contact with the blades, said the study published in the August 26 edition of the journal Current Biology.

Bats, which emit a sonar-like sound to detect objects, rarely collide with man-made structures, the researchers noted.

"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," said Erin Baerwald of the University of Calgary in Canada.

"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."

Birds have more rigid lungs than bats that allow them to more easily withstand sudden drops in air pressure.

The lungs of bats are balloon-like, with two-way airflow ending in thin flexible sacs surrounded by capillaries. A drop in air pressure can cause the sacs to expand too much, making the capillaries explode, the researchers said.

Bat deaths caused by wind turbines could have far-reaching consequences, the researchers warned.

While bats can live for 30 years or more, most only produce one or two pups at a time and not necessarily every year.

"Slow reproductive rates can limit a population's ability to recover from crashes and thereby increase the risk of endangerment or extinction," said Robert Barclay of the University of Calgary.

Their deaths could also affect ecosystems on the bats' migration routes as they eat thousands of insects, including many crop pests, every day, the researchers added.

Wind farms put pressure on bats
Richard Black, BBC News 26 Aug 08;

Bats are at risk from wind turbines, researchers have found, because the rotating blades produce a change in air pressure that can kill the mammals.

Canadian scientists examined bats found dead at a wind farm, and concluded that most had internal injuries consistent with sudden loss of air pressure.

Bats use echo-location to avoid hitting the blades but cannot detect the sharp pressure changes around the turbine.

The scientists say wind farms are more of an issue for bats than for birds.

"An atmospheric pressure drop at wind turbine blades is an undetectable - and potentially unforseeable - hazard for bats, thus partially explaining the large number of bat fatalities at these specific structures," said Erin Baerwald, who led the research team at the University of Calgary.

Route cause

Bat deaths around wind farms have been widely documented across Europe and North America.

Two years ago, EU nations formally agreed to make developers aware of the risks, and find ways of monitoring bat migration routes.

Earlier this year, a bid to build a wind farm near Bideford in north Devon was turned down because of the potential impact on the mammals.

But among all this, understanding of how turbines affect bats has been lacking.

The Calgary team collected carcasses of hoary and silver-haired bats killed at a wind farm in south-western Alberta.

Examinations showed that fewer than half had external injuries that could have been caused by collision.

But about 90% had internal haemorrhaging, most notably in the chest cavity, a condition that puts pressure on the lung and can be fatal.

The idea is that the pressure around a rotating turbine blade is lower than in the surrounding air. A bat flying into the low-pressure zone finds its lungs suddenly expanding, bursting capillaries in the surrounding tissue which then becomes flooded with blood.

Birds, which have more rigid and robust lungs, do not undergo the same trauma from a sudden drop in pressure.

"Given that bats are far 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," said Ms Baerwald.

Some research groups are investigating ways to keep bats away from wind farms, and a University of Aberdeen group recently suggested radar emissions might act as a "bat-scarer".

The new research is reported in the journal Current Biology.