Bats are generally considered harmless, albeit frightening, creatures of the night. But scientists have uncovered a wilder side after witnessing the great evening bat – Europe's largest bat species – hunt, kill and eat a robin in flight.
The terrifying footage reveals the bat to be a fearsome predator, soaring to heights of 1.2km (4,000ft) before launching into a breakneck dive in pursuit of its prey. When captured, the bat delivered a fatal bite, and subsequent chewing sounds recorded between echolocation calls revealed that the bat continuously consumed the bird during flight for 23 minutes without losing altitude.
“It's amazing that bats are able to not only catch them, but also kill and eat them while flying,” said Dr Laura Stidsholt, study co-author from Aarhus University. “A bird like this weighs about half as much as a bat itself—it’s like me catching and eating a 35-pound animal while jogging.”
Billions of birds migrate seasonally at night and over long distances at high altitudes, and their flight paths are known to intersect with bat hunting grounds. Dr Carlos Ibáñez of the Doñana Biological Station in Seville first proved that birds were an important food resource during the periods before hibernation (autumn) and gestation (spring) after observing feathers in bat feces 25 years ago. However, other scientists were skeptical, and over the years, Ibáñez and his colleagues installed surveillance cameras, military radars and ultrasonic recording devices attached to the balloons in search of conclusive evidence.
In the latest study, great evening bats were collected from birdhouses in the south. Spain and is equipped with tiny “backpacks” containing instruments for recording acceleration, pitch and sound, including echolocation signals. The data revealed two incidents of bat attacks on migratory birds, one of which was successful.
This bat was observed to rise to a height of 1.2 km before meeting its prey. “The bat flies in stealth mode,” Stidsholt said. “It's night now, the bird doesn't see it coming, doesn't hear the sounds of echolocation. The bat has an advantage.”
Upon approaching closely—perhaps alerted by the bat's wingbeats or its shadow—the bird suddenly entered a downward spiral. The bat was seen being chased in a cat-and-mouse game for over 1km, during which the microphone recorded 21 distress calls from the robin. As the pair approached ground level, the robin heard a final cry, 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 like it,” Stidsholt said. “But on the other hand, the bat is a very rare species and it doesn’t do very well in southern Europe due to drought and bushfires, so we want the species to feed well.”
Ibáñez previously collected and stored in a freezer severed wings of songbirds found under bat hunting grounds. X-ray and DNA analysis of 11 wings showed that the bats had bitten off and discarded the wings, likely to reduce weight and drag. Researchers believe the bats then stretch the membrane between their hind legs forward like a pouch, allowing them to eat the rest of the bird in flight.
Elena Tena, from the Doñana Biological Station and lead author of the study, said: “Although this creates sympathy for the prey, it is part of nature.”
The results were published in the journal Science.
