Ketu mice eat birds right in flight

The study, published in the journal Science, is the result of nearly 25 years of work and reveals unique details of an aerial hunt comparable in drama to aerial dogfights.

Every autumn, billions of songbirds migrate south. They fly at night, avoiding daytime predators. But the night skies aren't safe either - bats hunt in the dark. To understand exactly how they manage to catch and eat birds in flight, scientists fitted several individuals with miniature sensors (biologgers) developed at Aarhus University in Denmark.

These "backpacks" recorded movements, flight altitude, acceleration and even sounds, including echolocation signals. The data showed: the bats would climb to an altitude of more than a kilometre and begin a rapid dive, noticeably accelerating their wing flapping and releasing a series of attacking sounds.

One recorded instance lasted almost three minutes. The mouse eventually caught a Ribbon Thrush, which managed to emit 21 alarm calls before silence fell. The microphone then recorded 23 minutes of munching at low altitude - the mouse ate its prey on the fly. The animal is thought to tear the wings off the bird and use the leathery webbing between its hind legs as a pocket to hold the carcass.

Remarkably, the prey can be up to half the weight of the bat itself.

"It's like eating a 35kg carcass while jogging," explains Laura Stidsholt, one of the lead authors of the paper.

The facts are also striking in terms of manoeuvrability: the birds are known for their evasive manoeuvres in flight, but even that doesn't save them from nimble hunters in the sky. Scientists note that such skills are the result of evolution and extremely rare eating behaviour among mammals.

The hypothesis that nightjars hunt birds was put forward 25 years ago by Spanish biologist Carlos Ibáñez, who found feathers in the droppings of these animals. But only now, with the help of modern technology, it has been possible to document the process.

The authors emphasise that bats do not pose a threat to songbird populations: giant nightjars are extremely rare and endangered.