hunting

Bats eat the birds they pluck from the sky while on the wing

bats, Biology, birds, Ecology, hunting, Science / Kelly Newman / October 24, 2025

There are three species of bats that eat birds. We know that because we have found feathers and other avian remains in their feces. What we didn’t know was how exactly they hunt birds, which are quite a bit heavier, faster, and stronger than the insects bats usually dine on.

To find out, Elena Tena, a biologist at Doñana Biological Station in Seville, Spain, and her colleagues attached ultra-light sensors to Nyctalus Iasiopterus, the largest bats in Europe. What they found was jaw-droppingly brutal.

Inconspicuous interceptors

Nyctalus Iasiopterus, otherwise known as greater noctule bats, have a wingspan of about 45 centimeters. They have reddish-brown or chestnut fur with a slightly paler underside, and usually weigh around 40 to 60 grams. Despite that minimal weight, they are the largest of the three bat species known to eat birds, so the key challenge in getting a glimpse into the way they hunt was finding sensors light enough to not impede the bats’ flight.

Cameras, which are the usual go-to sensor, were out of the question. “Bats hunt at night, so you’d need night vision cameras, which together with batteries are too heavy for a bat to carry. Our sensors had to weigh below 10 percent of the weight of the bat—four to six grams,” Tena explained.

Tena and her team explored several alternative approaches throughout the last decade, including watching the bats from the ground or using military-grade radars. But even then, catching the hunting bats red-handed remained impossible.

In recent years, the technology and miniaturization finally caught up with Tena’s needs, and the team found the right sensors for the job and attached them to 14 greater noctule bats over the course of two years. The tags used in the study weighed around four grams, could run for several hours, and registered sound, altitude, and acceleration. This gave Tena and her colleagues a detailed picture of the bats’ behavior in the night sky. The recordings included both ambient environmental sounds and the ultra-frequency bursts bats use for echolocation. Combining altitude with accelerometer readouts enabled scientists to trace the bats’ movements through all their fast-paced turns, dives, and maneuvers.

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Even with protections, wolves still fear humans

This quickly became an issue, at least for some people. Mieczysław Kacprzak, an MP from Poland’s PSL Party, currently in the ruling coalition, addressed the parliament in December 2017, saying that wolves were roaming suburban roads and streets, terrorizing citizens—in his view, a tragedy waiting to happen. He also said children were afraid to go to school because of wolves and asked for support from the Ministry of Agriculture, which could lift the ban on hunting. An article in “Łowczy Polski,” a journal of the Polish hunting community with a title that translates as “The Polish Huntsman,” later backed these pro-hunting arguments, claiming wolves were a threat to humans, especially children.

The idea was that wolves, in the absence of hunting, ceased to perceive humans as a threat and felt encouraged to approach them. But it was an idea that was largely supported by anecdote. “We found this was not the case,” says Liana Zanette, a biologist at Western University and co-author of the study.

Super predators

To figure out if wolves really were no longer afraid of humans, Zanette, Clinchy, and their colleagues set up 24 camera traps in the Tuchola Forest. “Our Polish colleagues and co-authors, especially Maciej Szewczyk, helped us set those traps in places where we were most likely to find wolves,” Zanette says. “Maciej was literally saying ‘pick this tree,’ or ‘this crossroads.’” When sensors in the traps detected an animal nearby, the system took a photo and played one of three sounds, chosen at random.

The first sound was chirping birds, which the team used as a control. “We chose birds because this is a typical part of forest soundscape and we assumed wolves would not find this threatening,” Clinchy says. The next sound was barking dogs. The team picked this one because a dog is another large carnivore living in the same ecosystem, so it was expected to scare wolves. The third sound was just people talking calmly in Polish. Zanette, Clinchy, and their colleagues quantified the level of fear each sound caused in wolves by measuring how quickly they vacated the area upon hearing it.