Vampire bats are a common fixture of Halloween lore, but they are no longer alone in their macabre dining habits. Another bat species is now known to prey on birds during its nighttime hunts.
Researchers had previously detected songbird DNA in the droppings of three bat species, indicating that these flying mammals feast on more than just insects. But the hunting methods of these bats remained a mystery. The greater noctule, Europe’s largest bat, has now been reported as a skilled aerial predator capable of capturing, dissecting, and consuming migratory songbirds, as documented in the October 9 issue of Science.
For years, scientists struggled to uncover the techniques these bats use to catch their prey, especially since observing their activities in the high night sky is problematic. The breakthrough came when bioacoustician Ilias Foskolos from Aarhus University in Denmark suggested tracking their movement. He and his team outfitted greater noctules (Nyctalus lasiopterus) with biologgers that incorporated various sensors, such as accelerometers for 3-D movement recording, magnetometers for direction tracking, altimeters for altitude measurement and microphones.
“Utilizing these advanced technologies, the Science paper represents the first instance of tracking a greater noctule executing a hunting maneuver against a robin,” states Danilo Russo, a bat ecologist at the University of Naples Federico II, who was not part of the study. “Although there were no direct visual observations of the hunting process, I believe the findings provide strong evidence that birds are indeed captured in flight.”
While none of the sensors recorded video footage of the bats’ activities or meals, they did log each bat’s nightly adventures, offering researchers insights into their enigmatic hunting practices. Listening to the captured sounds is akin to soaring alongside the bats, says Elena Tena, a bat conservationist at Doñana Biological Station in Seville, Spain, where the researchers captured and tagged bats for the study. “You can hear the flapping” of their wings along with the calls of frogs as they navigate through the marshes of Doñana, she notes.
Microphones also recorded the feeding buzzes made as bats approached their prey. These buzzes, which were followed by sounds of chewing, indicated successful hunts, according to Tena. While the majority of the 611 hunting events involved near-ground insects, two significant instances involved hunting birds. In these cases, the bats ascended to impressive heights—over 1,200 meters, above the level of migrating songbirds. Subsequently, they honed in on a bird while producing loud feeding buzzes.
“The frequencies are so elevated that the birds cannot hear them,” explains Foskolos. Both birds reacted at the last moment, likely due to the bat’s touch or the sound of its wings. “They likely perform dives and spirals and complex maneuvers,” to evade their pursuers, he adds. “It appears they dive vertically down, based on the data we’ve collected.”
One bird managed to escape close to the ground. However, the other met a different fate. The microphones captured its distress calls followed by a 23-minute in-air meal. “The bat was flying normally according to the accelerometer data while simultaneously chewing and using echolocation,” says Tena. “At times, you could hear what seemed to be the crunching of bone.”
The removal of wings appears to be part of their hunting technique. “Every now and then, while we were capturing [bats], we’d notice wings suddenly dropping to the ground,” Tena mentions. Genetic analysis of wing injuries confirmed they were inflicted by greater noctule bats. Additionally, netted individuals from the same species have been found with blood-stained lips and feathers clinging to their mouths.
Although the research team has gathered compelling evidence of how these bats prey on songbirds, “we still know very little about this species,” Tena states. This study marks significant progress toward comprehending the greater noctule’s status as one of Europe’s foremost predators.
