Wind turbines are killing many thousands of bats contributing to a population decline that may be costing farmers millions of pounds, say researchers.
Scientists found the blades of wind turbines were a major threat to bats particularly when they are migrating.
Bats are useful to farmers because they eat large numbers of crop damaging insects, reducing the amount that has to be spent on pesticides.
Writing in the journal Science, the researchers estimated that bats could be worth billions to agriculture around the world.
Several migratory tree-living species of bats were being slaughtered “in unprecedented numbers” by wind turbines, said the researcher.
The work concentrated on North America but backs up research carried out in Britain that had similar findings.
Researchers urged policy-makers not to wait before addressing the issue of bat decline.
“Not acting is not an option because the life histories of these flying, nocturnal mammals – characterised by long generation times and low reproductive rates – mean that population recovery is unlikely for decades or even centuries, if at all,” said lead researcher Dr Gary McCracken, from the University of Tennessee at Knoxville.
According to the researchers, a single colony of 150 big brown bats in Indiana ate almost 1.3 million potentially damaging insects a year.
“Without bats, crop yields are affected,” said Dr McCracken.
“Pesticide applications go up. Even if our estimates were quartered, they clearly show how bats have enormous potential to influence the economics of agriculture and forestry.”