Wild bats have a long-term memory of sounds

Just like riding a bike, once we learn and retain skills, we rarely have to relearn them. Most studies on learning and long-term memory in the wild have focused on a handful of animal species. Now, researchers at the Smithsonian Tropical Research Institute (STRI) share the first report of long-term memory in frog-eating bats.

“Frog-eating bats are an excellent emerging model organism for studying cognitive and sensory ecology, learning plays a big part in their lives,” explained study lead author M. May Dixon.

When hunting frogs, the bat’s can identify the frog calls that indicate a frog is good to eat, compared to the calls that indicate a frog is poisonous, or even too big to carry.

For the study, 49 wild bats were trained to respond to ringtones played through speakers. When responding to two of the tones, a reward of fish was found, but three other tones were associated with no reward. 

The bats quickly learned when ringtones indicated a snack and ignored the ones that did not. The bats were then microchipped and released back into Panama’s Soberania National Park. 

The researchers recaptured some of the trained bats. When they played the experimental sounds again, the bats recognized and responded to the reward ringtones – even four years later. 

The ringtones sounded like the ping of a text message and the beep of a car being unlocked. Using human-generated sounds ensured that they wouldn’t be heard in nature.

As for the unrewarded sounds, the experts played one of them to the recaptured bats, and six of eight bats approached it. 

“It’s possible that they remember the extinguished sound, but enough time had gone by that they thought to check it out once more,” said Dixon. “Or it’s possible that they couldn’t remember the exact difference between the ringtones, and that extinguished sound was close enough to the rewarded one that they decided to check that out too. Sort of like a generalization of memory.”

To make sure that the bats were not responding to every sound they heard, a pure tone was played. Most of the bats did not fly to it, but only twitched their ears. 

This experiment raises more questions on how memory works in bats and other animals, including the metabolic cost of remembering. 

“I’m interested in memory capacity in animals and what causes long-term or short-term memories, what ecological conditions select for different memory lengths, what is important to remember and to forget,” explained Dixon. “But studying long-term memory is very difficult, because it takes a long time by definition. And testing memory in captive animals, even if it’s more convenient, isn’t necessarily representative of what animals can remember in the wild.” 

“STRI has been the basis for so much research done with bats. They have gathered a large database on frog-eating bats, on experiments done with bats, what stimulus have been used, so if you capture a bat that has been caught before, you already have its whole history. There are few places in the world where you can have that amount of detail.” 

“I went from liking bats but not thinking they were very interesting, to realizing they are very complex little creatures, with deep personalities and very engaging ways of interacting with the world.”

The study is published in the journal Current Biology

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By Katherine Bucko, Earth.com Staff Writer