A research team from the University of Calgary has found that a large percentage of bat fatalities at wind turbine sites are caused by a sudden drop in air pressure around the turbine blades, the BBC reports.

Reports of bat deaths at wind farms had previously been documented in Europe and the US, but quite why these generally exceeded the numbers of dead birds succumbing to the fatal blades had not been explained.

The Calgary team now says that while bats can use their echolocation to pinpoint the blades, they "cannot detect the sharp pressure changes around the turbine".

If a bat enters this zone, it can suffer "barotrauma" - internal haemorrhaging provoked by sudden expansion of the lungs* which puts pressure on surrounding tissue and bursts capillaries. Birds, which have more "rigid and robust" lungs, are less susceptible to the condition.

Lead scientist Erin Baerwald said: "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."

To prove their case, Baerwald and colleagues examined carcasses of hoary and silver-haired bats dispatched by a wind farm in south-western Alberta. They found that while "fewer than half had external injuries that could have been caused by collision", 90 per cent demonstrated internal haemorrhaging, "most notably in the chest cavity".

The findings indicated that "wildlife fatalities at wind turbines are now a bat issue, not a bird issue", Baerwald concluded.

The EU acted on the bat slaughter two years ago, before the exact cause was known, and "formally agreed to make developers aware of the risks, and find ways of monitoring bat migration routes". Accordingly, a proposal earlier this to build a wind farm near Bideford in north Devon was rejected "because of the potential impact on the mammals".

The Calagary team's findings are reported in the journal Current Biology. ®

Bootnote

*Just to clarify, the sudden drop in pressure expands the air already in the lungs. As our diving expert Lewis Page put it: "If the bat remembers to exhale when passing a wind turbine it should be ok."

Related stories

• Meat Loaf gets Q gong (30 September 2008)
• Wind farm wound down on air traffic fears (8 August 2008)
• Greenpeace: UK gov trying to strangle wind power (25 July 2008)
• Scottish gov OKs Europe's biggest onshore wind farm (21 July 2008)