Bats are generally viewed as harmless, if spooky, creatures of the night. But scientists have revealed a more savage side, after witnessing a greater noctule bat – Europe’s largest bat species – hunting, killing and devouring a robin mid-flight.

The grisly recording reveals the bat as a formidable predator, climbing to 1.2km (4,000ft) before embarking on a breakneck-speed dive in pursuit of its prey. On capture, the bat delivered a lethal bite and subsequent chewing sounds, recorded between echolocation calls, indicated that the bat consumed the bird continuously during flight for 23 minutes without losing altitude.

“It’s fascinating that bats are not only able to catch them, but also to kill and eat them while flying,” said Dr Laura Stidsholt, a co-author of the research based at Aarhus University. “A bird like that weighs about half as much as the bat itself – it would be like me catching and eating a 35-kilo animal while jogging.”

Billions of birds seasonally migrate at night and over long distances at high altitude and their flight paths are known to intersect with bat hunting grounds. Dr Carlos Ibáñez, of the Doñana Biological Station, Seville, first made the case that birds were an important food resource during the pre-hibernation – autumn – and gestation – spring – periods after observing feathers in bat faeces 25 years ago. Other scientists were sceptical, however, and in the intervening years Ibáñez and colleagues have deployed surveillance cameras, military radar and ultrasound recorders attached to hot air balloons in a quest for smoking gun evidence.

In the latest study, greater noctule bats were taken from nesting boxes in southern Spain and fitted with tiny “backpacks” containing instruments to record acceleration, altitude and audio, including echolocation calls. The data revealed two instances of bats mounting attacks on migratory birds, one of which was successful.

This bat was observed to climb to an altitude of 1.2km, before encountering its prey. “The bat is flying in stealth mode,” said Stidsholt. “It’s night-time, the bird can’t see it coming, it can’t hear the echolocation sounds. The bat has an advantage.”

On close approach – perhaps alerted by the bat’s wingbeats or its shadow – the bird suddenly entered a downward spiral. The bat was observed to follow in a cat-and-mouse chase covering more than 1km, during which the microphone recorded 21 distress calls from the robin. As the pair approached ground level, a final shriek was heard from the robin, followed by 23 minutes of chewing sounds from the bat as it continued to fly at low altitude.

“From a human perspective, I didn’t feel good about it,” said Stidsholt. “But, on the other hand, the bat is a very rare species and it isn’t doing very well in southern Europe due to droughts and wild fires so we want this species to have a good meal.”

Previously, Ibáñez had collected, and stored in a freezer, severed songbird wings found under bats’ hunting grounds. X-ray imaging and DNA analysis of 11 wings suggested that the bats bite off and discard the wings – probably to reduce weight and drag. The researchers believe that the bats then stretch the membrane between their hind legs forward like a pouch, allowing them to eat the rest of the bird mid-flight.

Elena Tena, of Doñana Biological Station and a lead author of the study, said: “While it evokes empathy for the prey, it is part of nature.”

The findings are published in the journal Science.