Giant bats eat birds mid-flight

The giant noctule bat has been found to prey on songbirds (Ana Popa)

A rare type of giant bat feeds on migratory songbirds as they fly – the first time this has been seen in the animal kingdom, say Swiss and Spanish scientists.

The researchers revealed on Wednesday that they had pinpointed evidence that the nyctalus lasiopterus bat preys on small birds migrating during the night over the Mediterranean.

The research, which was published in the Public Library of Science journal PLoS ONE, found that giant noctule bats, which have a 45-centimetre wingspan and weigh up to 70 grams, mostly ate insects in the spring but appeared to switch to bird meat during the autumn.

“There are some tropical bats that also feed upon birds or other small vertebrates like rodents and lizards,” said Raphaël Arlettaz, a professor of conservation biology at Bern University, who co-directed the team.

“What is new here is that we have a bat species which really feeds on migratory flying birds high in the sky – this is the first time this has been seen in the animal kingdom,” he told swissinfo.

It is still unclear whether the bats have always eaten birds or whether this is a recent development in response to an abundance of food, said Arlettaz.

But what is certain is that the ability of these bats to feed on very large insects was probably a prerequisite for exploiting the birds, he added.

Controversy

The team, which includes scientists from the Consejo Superior de Investigaciones Cientificas in Seville, Spain, had previously reported finding bird feathers in the faeces of bats.

This created controversy, with some biologists maintaining the bats must have accidentally eaten feathers floating in the air.

The Swiss and Spanish scientists decided to investigate further and analysed the bats’ blood throughout the year.

Chemical variants called isotopes can tell what an animal has been eating, and carbon and nitrogen isotopes are especially useful for finding out what exactly it has been feeding on.

Using this technique, the biologists found strong evidence that the flying mammals preyed heavily on birds in the autumn, when there is the most migration. In summer they ate insects and in spring they were found to have ingested a mix of birds and insects, said Arlettaz.

Every year approximately five billion songbirds cross the Mediterranean basin during their autumn migrations, said the researchers. Many are small, which make the birds potential targets for the bats.

Significant discovery

Arlettaz said the next step would be to find out how the bats capture the birds in the air and how they handle them afterwards to get the meat.

A second aspect would be to identify which species of birds are captured and eaten. For this, DNA techniques on feathers retrieved in the droppings could be used, he said.

Arlettaz is convinced that the team’s discovery is a significant one.

“It shows that we don’t know everything about nature,” he said. “And that we still have a lot of things to uncover regarding the specialisation of species for exploiting the most abundant food resources like these migratory birds.”

swissinfo, Isobel Leybold-Johnson

In brief

Bats are known to exploit a wide array of food sources including arthropods, pollen, fruit, small terrestrial vertebrates and even blood.

They are praised for scooping up mosquitoes and other pests, but they are also reviled for drinking blood and spreading rabies.

Tare giant noctule bats, which have a 45-centimetre wingspan and weigh up to 70 grams, are Europe’s largest bats.