Fringe-lipped bats, also called frog-eating bats, are named for their unusual wart-like bumps on their lips and muzzle. They snack on Tungara frogs, which they locate by listening to their calling sounds, and can also use their echolocation abilities to detect water ripples surrounding the frogs — even long after the frogs stopped calling.

While these bats have been studied by researchers in the past, their learning and long-term memory in the wild has largely remained a mystery. Now, a group of researchers working at the Smithsonian Tropical Research Institute (STRI) found that the bats can remember the sounds of their prey (frogs and large insects) for up to four years.

The STRI researchers, led by May Dixon, trained a group of 49 fringe-lipped bats (Trachops cirrhosus) to respond to cellphone ringtones played through speakers. The ones that responded to two of the tones found a bait fish reward on the speaker every time, while the bats that responded to three other tones were never rewarded.

The bats quickly learned to fly to the speaker only when ringtones indicated a snack, and not to respond to the other tones. They were then microchipped and released into the wild. One to four years later, the team recaptured eight trained bats. When they played the experimental sounds again, the bats recognized and responded to them.

“This is truly extraordinary,” Rachel Page, a study co-author and researcher at STRI, told The Daily Texan news website. “It would be like remembering cues associated with a meal you had four years later. We now know that these bats have the potential for very long memories for prey cues, and don’t have to relearn them each time.”

Bats with a long memory

The ringtones the researchers chose for the experiments weren’t random and included the beep of a car being unlocked and the ping of an incoming text message alert, for example. They sounded clearly human-generated, so the bats wouldn’t hear them in the wild but were also frog-like enough in order to make the bats sufficiently interested.

“The reason we use these sounds is (because) they are something the animals would never hear in the wild,” Dixon, a postdoctoral scholar, said in a statement. “We could be sure that the only experience the animals had with it was the experience that we train them with. But it’s actually not that dissimilar to the sounds of the frogs.”

The experiment raises further questions regarding how memory works in these bats and other animals. Studying long-term memory is very difficult as it takes a long time by definition, the researchers said. And while testing memory in captive animals is convenient, it’s not necessarily representative of what animals remember in the wild.

Their long memory could be helping the bats know which frogs to approach and which not to, and could also enable them to eat seasonal frogs without having to relearn their calls after long periods, Dixon said. In the future, she said she would like to carry out comparative studies to see how this bat’s memory compares to other bats and animals.

The study was published in the journal Current Biology.