After 25 years, scientists solve the bird-eating bat mystery

An international research team has uncovered how this massive bat hunts and eats its prey. Their findings, published in Science, reveal an astonishing story of night-time aerial chases, precision attacks, and predation in total darkness.

Each year, billions of songbirds migrate between breeding and wintering grounds. Many travel at night and at high altitudes to avoid daytime predators. Yet flying in darkness comes with its own dangers, as bats rule the night skies.

Riding on the Bats' Backs

To understand these elusive hunters, scientists effectively "rode along" with Europe's largest bat -- the greater noctule (Nyctalus lasiopterus) -- by fitting individuals with tiny "backpacks" containing biologgers developed at Aarhus University. These lightweight devices measured the bats' altitude, acceleration, movement, and sounds (including their echolocation calls), providing an unprecedented look at their nocturnal hunting strategies more than a kilometer above ground.

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.

Their success depends 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 -- 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.

Combined with X-ray and DNA analysis of bird wings found beneath hunting areas, these results confirm what happens next: the bat kills the bird with a bite, removes its wings (likely to reduce drag), and then uses the membrane between its hind legs as a pouch to hold and eat the prey while still airborne.

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.

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.

His team has closely monitored this elusive forest-dwelling species using "smart" roosts equipped with antennas to detect implanted microchips in the bats. The system tracks movements, stores data, and sends alerts to researchers' phones in real time.

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.

Essential for Bat Conservation

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.