In a scene right out of a horror movie, audio recordings have confirmed that Europe’s largest bat, the greater noctule (Nyctalus lasiopterus), tracks, kills, and eats its prey in mid-flight without landing.
Scientists have previously suspected that the greater nocturne was killing and eating robins and other small birds, but they were unsuccessful in capturing the grizzly behavior in real-time because bats are highly maneuverable and hunt at night.
The latest effort utilized miniaturized microphones and advanced tracking sensors to record the behavior in real-time, eliminating any doubt whether the bats landed to consume their prey.
“We knew we had documented something extraordinary,” said the study’s lead author, Elena Tena from Aarhus University, when detailing the victim’s cries and subsequent “chewing” sounds on the recording that confirmed the large bats were killing and consuming the robin in mid-flight. “I had to listen to it several times to fully grasp what we had recorded.”
According to a press release detailing the shocking discovery, Spanish bat researcher Carlos Ibáñez and his colleagues at the Doñana Biological Station (CSIC) in Seville had long suspected that bats feasted on songbirds during their migrations between breeding grounds and other wintering areas, especially since the birds would often travel at night to avoid diurnal predators. Although they had previously discovered feathers in the droppings of greater nocturne bats and gathered other supporting evidence over 25 years of diligent research, they still lacked the direct evidence to support their oft-criticized hypothesis.
The idea was further complicated by the fact that some birds weigh up to half the weight of the hunting bat, which the researchers note “might reduce the bats’ ability to fly.” Still, the team had collected enough indirect evidence to be confident it was happening.
“We knew that the greater noctule catches and eats insects in flight, so we assumed it did the same with birds,” Ibáñez explained. “But we needed to prove it.”
Due to the difficulty in directly observing and recording nighttime hunting behavior of bats, the CSIC team had previously tried surveillance cameras on roosts, military radar, ultrasound recorders attached to hot-air balloons, and GPS trackers. Unfortunately, most technologies were too heavy or bulky to directly attach to the bats.
In the latest study, Tena and Assistant Professor Laura Stidsholt from the Department of Biology at Aarhus University used lightweight custom-made devices, called biologgers or “backpacks,” that were affixed to trapped bats before releasing them back into the wild. Designed to track the animal’s movements, acceleration, altitude, and sounds, including the bat’s echolocation calls used for navigation, the team said the backpacks would reveal the bat’s hunting techniques “as they pursue prey more than one kilometre above the ground in total darkness.”
After equipping a pair of bats with the biologger backpacks, the team was able to monitor their hunting behavior in previously unavailable detail. For example, the data showed that the bats fly high in the air and then attack in a rapid descent, similar to a fighter pilot’s dogfighting technique. The data also revealed that the birds were unable to hear the bat’s echolocation calls, resulting in virtually no warning before they were attacked.
In one of the team’s outings, one of the sensor-equipped bats was recorded plunging vertically for 30 seconds to pursue their prey, before abandoning the unsuccessful chase. Stidsholt said the team knew that songbirds perform “wild evasive manoeuvres” such as spirals and loops to escape hawks and other daytime predators during the day, “and they seem to use the same tactics against bats at night.”
A second, seemingly more determined bat, was recorded accelerating in an attack plunge for a total of 176 seconds before successfully capturing a bird. In both the successful and unsuccessful attacks, the team said their sensor package captured the skilled hunters “beating their wings faster and harder and tripling their acceleration while emitting continuous attack calls.”
When analyzing the recording of the second bat’s nearly three-minute pursuit, the team found it caught its prey close to the ground but did not land to kill and consume it. Instead, the microphone recorded 21 distress calls from the captured robin, followed by what they described as “23 seconds of chewing sounds” as the bat continued along at low altitude.
Tena said that while the recording “evokes empathy for the prey,” the entire process is simply “part of nature.” As for the team, the researcher said the explicit recording of a bird being killed and consumed in mid-air “confirmed what we had been seeking for so long.” Stidsholt notes that although the recording gives the team some justification against critics, she must admit it is still hard to fathom the scene actually taking place.
“It’s fascinating that bats are not only able to catch them, but also to kill and eat them while flying,” the professor said. “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.”
The study “Greater noctule bats prey on and consume passerines in flight” was published in Science.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.