After nearly 25 years of research, an international team of scientists has finally solved a mystery: The greater noctule, Europe's largest bat, doesn't just eat small birds - it hunts and captures them more than a kilometre above the ground and it eats them without landing.
Greater noctule hunt Nyctalus lasiopterus with feather in mouth | Photo by Jorge Sereno
In an article now published in the journal "Science", the team analyses data from greater noctules tagged with miniaturised biologgers in the Doñana Biological Station in Spain and reconstructs in detail how the bat achieves the hunt and the meal mid-air.
Every year, billions of songbirds migrate between their breeding grounds and wintering areas. Many species fly high and travel at night, partly to avoid daytime predators. But that doesn't make the journey risk-free - bats hunt at night. The new scientific investigation led by Laura Stidsholt from the Aarhus University, and Carlos Ibáñez and Elena Tena from the Doñana Biological Station shows that some bats can fly high into the night sky to locate and attack unsuspecting birds. The team equipped greater noctules (Nyctalus lasiopterus) with tiny "backpacks" containing biologgers that record the bats' position, acceleration, altitude, and sound, revealing their hunting techniques.
A hunt reconstructed with biologger data
Among the more than 600 hunts from 14 greater noctules that the team investigated, two stood out: In contrast to their regular insect hunts, which are characterised by short chases of mostly less than 10 seconds and low flying heights of on average 53 metres above ground level, the bats soared high into the sky, signalled the attack by a rapid burst of short echolocation calls and pursued their prey in steep, breakneck-speed dives towards the ground. They plunged vertically for 30 and 176 seconds respectively, beating their wings faster and harder and tripling their acceleration while emitting continuous attack calls. The bat that dived for 30 seconds eventually gave up - birds are at least as agile in the air as bats. The second bat, however, caught its prey - a robin - close to the ground after nearly three minutes of pursuit. The logger's microphone recorded 19 distress calls from the bird, followed by 23 minutes of chewing sounds from the bat as it flew at low altitude. Combined with X-ray and DNA analyses of songbird wings found under the bats' hunting grounds, the data paint a clear picture of the final act: The bats kill the birds by biting them, then bite off their wings - probably to reduce weight and drag. The scientists believe that the bats then stretch the membrane between their hind legs forward like a pouch and eat the bird mid-flight.
"We know that songbirds perform wild evasive manoeuvres such as loops and spirals to escape predators like hawks during the day - and they use the same tactics against bats at night. It's fascinating that bats are not only able to catch them, but also to kill and eat them while flying. 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," says Assistant Professor Laura Stidsholt from the Department of Biology at Aarhus University. She is the study's first author and has for several years refined and applied biologger technology in her bat research, leading to numerous scientific papers - and surprises. At the time when she finalized the data collection and did the analysis for this paper, Stidsholt was a Postdoc in the Prof. Christian Voigt's bat research group at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) in Berlin.
Catching a bat in the act and solving a 25-year-old mystery
For a couple of decades, it has been known that at least three large bat species feed on small birds in flight. Much of this knowledge stems from the work of Spanish bat researcher Carlos Ibáñez and his colleagues at the Doñana Biological Station in Spain. Nearly 25 years ago, Ibáñez discovered feathers in the droppings of greater noctules and has since gathered mounting evidence that these bats catch and eat songbirds. For years, the scientists tried to uncover exactly how the bats achieve this daring stunt. "We knew that the greater noctule catches and eats insects in flight, so we assumed it did the same with birds - but we needed to prove it," says Carlos Ibáñez. The hypothesis was initially met with scepticism within the scientific community, since some birds weigh up to half the weight of the bat itself and thus might reduce the bats' ability to fly.
Because bats hunt at night, it is impossible to film the chase. Scientists instead tried surveillance cameras on roosts, military radar, ultrasound recorders attached to hot-air balloons, and GPS trackers. The main challenge was finding equipment light enough for the bats to carry. Such lightweight devices have been under development at Aarhus University. And now - just as Carlos Ibáñez approaches retirement - the team has finally caught a greater noctule in the act. For Elena Tena, also a lead author of the study, hearing the sound recording of the bird's distress calls followed by sudden silence and long chewing noises was an intense moment after so many years of effort: "While it evokes empathy for the prey, it is part of nature. We knew we had documented something extraordinary. For the team, it confirmed what we had been seeking for so long. I had to listen to it several times to fully grasp what we had recorded."
Greater noctules are no threat to passerine birds - and themselves endangered
Fortunately, there is little cause for concern about bats threatening songbird populations. The greater noctule is extremely rare and, in many areas, endangered as its forest habitats disappear. Prof. Christian Voigt, head of the Leibniz-IZW Department of Evolutionary Ecology, says: "We must ensure that we protect both migratory birds and their predators. For the greater noctule bat, this means, in particular, natural forests with old trees rich in cavities."
Stidsholt L, Tena E, Foskolos I, Nogueras J, de la Hera I, Sánchez-Navarro S, García-Mudarra JL, Ibáñez C (2025):
Greater noctule bats prey on and consume passerines in flight.
SCIENCE. DOI: 10.1126/science.adr2475
