Only a dozen known bat species are carnivorous

Until now, it was thought that bats rarely preyed on birds and then only resting ones.

But it seems that birds crossing the Mediterranean during spring and summer provide a tasty meal for the greater noctule bat, one of the continent's rarest mammals.

Carlos Ibanez, of Estacion Biologica de Donana, Seville, Spain, and co-researchers said: "Millions of small birds concentrate and cross over the world's temperate regions during migration, mainly at night, but no nocturnal predators are known to benefit from this enormous food resource."

He said an analysis of the bat's droppings revealed that it captured and ate large number of migrating birds "making it the only bat species so far known that regularly preys on birds".

Insect-eaters

Other evidence came from the bat's flight performance and the range and frequency of sound waves it used to capture its prey.

"The echolocation characteristics and wing morphology of this species strongly suggests that it captures birds in flight," the team added.

Greater noctule bat

Largest European bat Feeds on flying insects Found in Mediterranean region Wing span of 450 mm Weighs 50g

The greater noctule bat (Nyctalus lasiopterus), which is extremely rare, is found mainly in Spain and Italy. A smaller relative is seen in the UK.

Most bats are insectivorous, but a few types, mainly large tropical bats, are meat-eaters.

The new research is reported in the journal Proceedings of the National Academy of Sciences.

"These findings are very interesting and surprising," said Andreas Streit, executive secretary of Unep- (United Nations Environment Programme) Eurobats, which monitors bat conservation in Europe.

"A lot of follow-up research will be needed," he told BBC News Online.