Unveiling the Nighttime Hunter: A Quarter-Century Mystery Solved
After 25 years, scientists have finally solved the enigma of the bird-eating bat, revealing a captivating story of aerial predation in the dark.
For nearly a quarter-century, scientists have been captivated by the behavior of Europe's largest bat, the greater noctule (Nyctalus lasiopterus). Contrary to popular belief, this massive bat doesn't just snack on small birds; it actively hunts and consumes them while in mid-flight, more than a kilometer above the ground. This remarkable discovery, published in Science, sheds light on the intricate strategies of these elusive night-time hunters.
Each year, billions of songbirds migrate between breeding and wintering grounds, navigating the night skies to avoid daytime predators. However, these nocturnal journeys come with their own set of dangers, as bats rule the night skies. To understand these elusive hunters, scientists effectively 'rode along' with the greater noctule by fitting individuals with tiny "backpacks" containing biologgers developed at Aarhus University. These lightweight devices measured the bats' altitude, acceleration, movement, and sounds, providing an unprecedented look at their nocturnal hunting strategies.
The data revealed that the bats soar high into the night sky to find and ambush unsuspecting birds. Unlike insects, birds cannot detect the bats' ultrasonic calls and only realize the danger moments before being caught. The bats' success relies on powerful, low-frequency echolocation calls that can detect birds at long distances. When they close in on a target, the bats unleash rapid bursts of short calls, signaling the final stage of attack.
Daring Dives
Information from the biologgers showed that the bats plunge toward their prey in steep, high-speed dives reminiscent of fighter jets in combat. In two documented chases, the bats dove for 30 and 176 seconds respectively, flapping harder, tripling their acceleration, and continuously emitting attack calls. The first bat eventually abandoned its pursuit, as birds are agile aerialists too, but the second succeeded after a nearly three-minute chase, capturing a robin near the ground. Microphones recorded 21 distress calls from the robin, followed by 23 minutes of chewing as the bat flew low, feeding on the wing.
Wild Maneuvers
"We know that songbirds perform wild evasive maneuvers such as loops and spirals to escape predators like hawks during the day -- and they seem to 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," explains Assistant Professor Laura Stidsholt from the Department of Biology at Aarhus University.
Stidsholt, a lead author of the study, has spent years perfecting biologger technology in bat research, resulting in numerous discoveries. When she completed the data collection and analysis for this project, she was a Postdoc at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) in Berlin. The 25-year hypothesis has finally been confirmed, thanks to the tireless efforts of scientists like Stidsholt and her team.
A 25-Year Hypothesis Confirmed
For decades, scientists suspected that some large bat species prey on small birds during flight. Much of that work originated from Spanish bat expert Carlos Ibáñez and colleagues at the Doñana Biological Station (CSIC) in Seville. Nearly 25 years ago, Ibáñez found bird feathers in greater noctule droppings and spent years gathering evidence that these bats were indeed bird predators. Despite the evidence, the idea that bats could catch birds midair was met with skepticism, as birds can weigh nearly half as much as the bats themselves. Filming these hunts proved impossible in the dark. Over the years, researchers experimented with roost cameras, military radar, hot-air balloons with ultrasound recorders, and GPS trackers -- struggling to create tools light enough for the bats to carry.
Finally, with new miniature biologgers from Aarhus University -- and just as Ibáñez neared retirement -- the team succeeded in recording a greater noctule hunting and eating a bird in flight. For co-author Elena Tena, hearing the recording was both thrilling and sobering:
"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."
Fortunately, these bats pose no threat to songbird populations. The greater noctule is extremely rare and endangered in many regions due to the loss of forest habitats. Understanding its behavior and ecology is now vital for developing conservation and management strategies that can help protect one of Europe's most extraordinary nocturnal predators.
