Giant Bats Snatch Birds from Night Sky

Morning Edition, April 18, 2007

Every spring, billions of migratory songbirds in Europe fly north to their breeding grounds. Most of these birds fly at night when no predators are around — or so the experts thought. But researchers have now found evidence of a giant European bat that is plucking migrating birds out of the night sky.

Several months ago, a group of bat researchers spent the night recording the sounds of a marshy Spanish forest. When they played the recordings back at full speed, they could only hear the croaking of the frogs. But when the researchers played the recordings back at one-tenth their normal speed, they heard shrieks — the radar call of a creature called the giant noctule bat or Nyctalus lasiopterus.

This bat is hairy and brown, with a wingspan slightly bigger than a blue jay's. It is one of Europe's largest bats and it has a huge mouth full of scary-looking teeth. It is one of the least-known bats in all of Europe — it spends its days hiding out at the tops of tall trees.

"They are not so easy to see if you don't know that they are there, so most people don't know that they exist," says Ana Popa-Lisseanu of the Doñana Biological Station in Sevilla, Spain.

Popa-Lisseanu is an expert on giant noctules, and says it has long been known that these bats feed on flying insects. What wasn't known until recently is that the giant noctule may be the only bat that eats birds on the wing. Popa-Lisseanu thinks it starts when the noctules fly thousands of feet up into the night sky. Then they use radar calls to lock in on a migrating songbird beneath them. Then the bat swoops in for the kill.

"They wrap the prey between their wings and the tail membrane," Popa-Lisseanu says, "so they make kind of a cage for the bird."

She says the bats eat just the "most profitable parts" of the migrating bird, such as the breast, where birds accumulate fat and muscle.

When they get close to the ground, the bats open their wings and drop the mangled carcasses. No one has ever seen one of these meals on the fly, but researchers have been pulling feathers out of the bat's feces for years. Now, in the journal Public Library of Science, Popa-Lisseanu and her colleagues say blood and tissue tests show that birds are a major food source for the giant noctule bats.

"It was something that shocked all bat scientists," she says.

The team compared the different chemical fingerprints that insects and birds leave in the bats that have eaten them. The researchers found that in the summer, the bats ate only insects, but during the spring and fall migrations, they ate many birds.

Giant noctule bats are far too rare to pose a major threat to migratory songbirds, but the recent paper is still attracting plenty of attention. Peter Marra, a songbird expert with the Smithsonian Institution, says that's because the bat's behavior is so interesting.

"It makes complete sense," Marra says, "because there's so much biomass that it's not surprising that there's a species taking advantage of it. And it's really neat that a bat is doing it."

Popa-Lisseanu says her research team is continuing its studies. The researchers are working with electronic radars, and hoping to catch one of the giant bats as it homes in on a flying songbird.

This was found at NPR.