These Lazy Bats Are Super-Efficient Killers That Carefully Conserve Energy to Attack at a Moment’s Notice

In the pursuit of radio-tagged bats, Leonie Baier has gotten her truck stuck in the mud in the middle of the jungle with no cellphone reception. She has waited patiently outside a cave for an entire night, a beeping signal on her tracking device indicating the creature was close—only to realize the following morning that the flying mammal had been in a different cave nearby. She has waded neck-deep into a flooded underground passage, sometimes diving under root clusters to reach her quarries.

That’s because she must collect the tracking devices glued to the bats if she hopes to recover the precious data contained on them. “I do anything I can to get that logger back,” says Baier, of the Naturalis Biodiversity Center in the Netherlands.

Now, these investigations by Baier and her colleagues have revealed an “entirely surprising” result: The predatory fringe-lipped bats they work so hard to find are much more successful at catching their targets than the researchers are at capturing them. While Baier sometimes struggles to find a bat she knows is tantalizingly close, the animals are highly accurate hunters when they leave their roosts to snag a meal, despite sometimes putting in very little effort.

In a study published recently in Current Biology, the team found fringe-lipped bats have a more than 50 percent success rate in capturing their prey and waste little energy doing it. “The success rate [of fringe-lipped bats] is crazy,” says Teague O’Mara, director of conservation evidence at Bat Conservation International, who was not involved in the research.

Some other predators, like porpoises and dragonflies, achieve success rates above 90 percent by catching abundant, small prey. But the fringe-lipped bats capture prey that’s typically about 7 percent of their body mass—and sometimes nearly as large as the bat itself. This puts them ahead of the likes of leopards, lions and polar bears, which also capture bigger prey but boast success rates of only 20 percent, 14 percent and 2 percent, respectively.

It turns out, the bats’ trick is an unusual survival strategy that lets them work smarter rather than harder. “They have giant ears—they just hang there and listen,” Baier says.

Fringe-lipped bats, named for the bumps around their mouth and nose, are found from southern Mexico down to Brazil and Bolivia. In Panama, they often prey on túngara frogs, amphibians a little smaller than a golf ball with mating calls that are easily pinpointed by the right set of big ears. The bats find these frogs by listening for their vocalizations—meaning that the amphibians’ best efforts to find mates sometimes work against their very survival. “They announce themselves: ‘Hello, I’m dinner, I’m here,’” says Baier.

Much of the research on these frog-eating bats was done in captive settings due to the difficulty of studying them in the wild. “They are fast, they are small, they are on the wing, and it’s nighttime,” says Baier, who was a postdoctoral fellow at the Smithsonian Tropical Research Institute in Panama and Aarhus University in Denmark at the time of research. But because tracking devices are getting ever smaller, Baier and her colleagues saw an opportunity to learn more about how these carnivorous bats find success outside the walls of the lab.

The team captured bats in March and October 2023 in Soberanía National Park, near the town of Gamboa, Panama. This part was relatively easy, as they went to known sites with larger roosts. They caught around 100 bats.

They then fitted each bat with a small radio-tracking device, an accelerometer, a magnetometer and an ultrasonic microphone that could record things such as echolocation and chewing. The whole getup was about the size of a gummy bear. They affixed these to the bats’ back fur using a skin glue that dissolves after a couple of days.

Between one and five days later, Baier and her colleagues went back to the same area where they caught the bats, and they homed in on the trackers using radio-telemetry devices. Given the difficulty of finding a tagged bat, the team got back workable data from only about 20 of the devices. The rest either didn’t work, or the researchers couldn’t find the bat again. “It’s difficult, but to me it’s also the most fun part,” says Baier.

Once the bats were caught, the researchers removed the trackers; they also weighed and measured the bats, took fecal and hair samples, and counted parasites.

“What we found mostly was that they don’t do much—that was the most astonishing for me,” Baier says. They spent only about 11 percent of their time flying. The rest was sleeping, eating or waiting, perched on tree branches or other structures, listening for prey.

“It’s pretty incredible insight about a bat,” says O’Mara.

Listening to the recordings, Baier could visualize what the bats were doing when the action did kick off. She’d hear a chorus of frog calls nearby and sometimes the echolocation of other bats, then the subject would take wing—motion confirmed by the accelerometer and magnetometer.

“All of a sudden, you can hear one frog getting really, really loud, then it goes quiet,” Baier says. More flying ensued, then the clear sound of a bat diving into a lip-smacking meal. Baier likes to mimic the chewing noise.

It wasn’t always small frogs. In one case, Baier was straining to listen to low-volume sounds on the recording. Then, she says, “my ears almost exploded”—whatever this bat had caught was putting up a real fight, and loudly. She found several more of these cases, with what sounded like larger prey. The struggle usually ended with a crunch. Baier assumes it was the bat biting into its prey’s skull.

Baier’s team used the length of a bat’s chewing to estimate the size of its prey. In one case, the bat ate for nearly half an hour—much longer than the average eight minutes it takes to consume a túngara frog. Accelerometers showed the bat likely fell asleep after starting the meal, then woke up and began to chew again without leaving its perch. “These bats don’t even let go when they fall asleep,” Baier says.

The cycle happened several more times—it took the bat 84 minutes of eating time spread throughout half the night to finish with this food. Follow-up experiments revealed that whatever the creature was—fringe-lipped bats also prey on lizards, hummingbirds and even other bats—it was nearly as big as the predator itself. The largest prey caught by the bats ranged from 17 to 30 grams.

But most often, the bats consumed prey of about 1.7 grams, which roughly aligns with the size of a túngara frog.

While bats did sit around eavesdropping for frogs, they also hunted more actively. Just over half of their attacks were launched from flight rather than from a perch. They seemed to hunt chirping frogs more from the air, possibly since the amphibians’ loud calls can be more easily heard over the noisy atmosphere of flying, the researchers suggest. While perched, the bats were more likely to attack non-vocalizing prey, perhaps because it’s easier to listen to subtler noises for a bat that sits still.

Overall, the bats were extremely successful when they went on the chase. Though they made a kill about half the time on average, some individuals were much more talented. “I was very proud of my bats,” Baier says. “They were so good.”

What sets the bats apart is not only their success, but also their efficiency. Some large carnivores have higher success rates—African wild dogs, for example—but most spend a lot more energy to find and kill their prey across wide geographic ranges. These bigger animals can store lots of energy in their bodies, allowing for high-intensity pursuits or days-long bouts of stalking that might only rarely end with a kill. Fringe-lipped bats, meanwhile, don’t travel very far from their roosts to hunt. As small-bodied animals, the bats must survive by burning their limited fat reserves until they catch their first meal of the night. Precision is paramount. “We are thinking this only works because they have so much prey around,” Baier says.

But she’s concerned that many of the forest habitats around wetlands suitable for túngara frogs are disappearing. If humans encroach on too many of these wetlands, or other factors like disease or climate change take a toll on frog populations, it may not be so easy for fringe-lipped bats to catch a meal. “Their whole strategy won’t work anymore,” Baier says.

O’Mara says that many bats live at the edge of their metabolic ceiling—their limit for energy expenditure—so their ability to thrive in the wild depends on abundant prey. “It’s incredibly important to protect those kinds of forest.”