Wind turbines can spin at up to more than 280 kilometres an hour, and blades can stretch to 40 metre

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Holger Goerlitz, of the Max Planck Institute for Ornithology in Seewiesen, Germany, and colleagues report in the Proceedings of the Royal Society Interface that they looked at the challenge ads faced by bats that hunt with ultrasound.
Around 1,000 species of bat use echo-location to identify prey and head for it. They emit an ultrasonic squeak, and wait for the echo as the sound returns from a fat insect that might make a tasty snack.
But the carrying capacity of the air is affected by temperature and humidity. As temperatures rise, bats that make the highest ads frequency squeaks could be at a disadvantage, the authors report. This is because warmer air is more likely ads to attenuate sound, and therefore limit the range at which a hungry bat can pinpoint its next mouthful.
Bats that emit the highest frequency sounds to hunt will find their kill zone more limited. Paradoxically, those bats that work with the lowest frequencies will find that global warming works more to their advantage, the researchers say.
The scientists took temperature and humidity data for May to September during the hunting hours after sunset in Germany as the basis for their calculations, and similar data from Malaysia for comparison.
We found a consistent pattern that across bat species with different call frequencies, rising temperature will lead to increased detection volume at lower frequencies and reduced detection volume at higher frequencies , they report.
Mark Hayes at the University of Colorado, Denver used evidence of dead bats found in the vicinity of wind turbines to arrive at a new figure for bat slaughter in the US. He reports in the journal BioScience .
Wind turbines can spin at up to more than 280 kilometres an hour, and blades can stretch to 40 metres. Hayes made his analysis of the dead bats near wind farms, ads and arrived at what he warns is a conservative estimate for bat deaths per megawatt of installed wind energy.
There are 45 species of bat in the contiguous United ads States: they catch insect pests like mosquitoes, and they also pollinate some important crops, so their loss could have consequences for human society.
But it is important to keep the numbers in perspective. Neither global warming nor renewable energy are the real threats to bats, or for that matter birds. Most human activity is a menace to nature s flying objects.
Wind farms are estimated to have killed more than 570,000 birds in the US last year, including protected and iconic predators such as the bald eagle. But around a billion birds are estimated to have died flying into windows.
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