Wild bats can remember sounds for years
There are certain skills that once we learn them we rarely have to relearn, like riding a bike or looking both ways before crossing a street. Most studies of learning and long-term memory in nature focus on a handful of animal species. Now in a post in Current biologyresearchers working at the Smithsonian Tropical Research Institute (STRI) share the first report on long-term memory in frog-eating bats (Trachops cirrhosis).
“Frog-eating bats are an excellent emerging model organism for studying cognitive and sensory ecology,” says biologist M. May Dixon, lead author of the paper, who just completed his PhD at the University of Texas to Austin, “learning plays a big role in their lives.”
Bats’ ability to learn and retain information means that when they hunt frogs, their primary prey, they don’t have to constantly relearn what frog calls indicate a frog is good to eat, poisonous or too big to carry.
Dixon and his colleagues trained 49 wild bats to respond to cellphone ringtones played through loudspeakers. Bats responding to two of the tones found a baitfish reward on the loudspeaker each time, but when they responded to three more tones, they were never rewarded. They quickly learned to fly to speakerphone when ringtones indicated a snack, and not respond to other tones. The bats were then microchipped and released into Soberania National Park in Panama.
The researchers captured eight trained bats between one and four years later, and when they played the experimental sounds again, the bats recognized and responded to the two rewarded tones even four years later. For comparison, the experiment included 17 untrained frog-eating bats that generally flicked their ears attentively but did not fly toward sounds.
When Dixon was working as a STRI intern with doctoral student and co-author Patricia Jones to find out if bats could learn which new tones meant a reward by watching other bats’ responses, she realized that she could also tell if bats could remember tones.
The ringtones they chose for the experiments, the ping of an incoming text message alert and the beep of a car being unlocked, sounded clearly man-made, so bats wouldn’t hear them. not by chance in the wild, but frog-like enough that bats were interested.
As for the extinguished tones, the unrewarded ones that the bats have learned to ignore, the researchers played one to the recaptured bats, and six of the eight trained bats came close.
“It’s possible they remembered the sound off, but enough time had passed that they thought to check it one more time,” Dixon said. “Or it’s possible that they don’t remember the exact difference between the rings, and that the off sound was close enough to the rewarded sound that they decided to check that too. Sort of like a generalization from memory.
To make sure the bats didn’t respond to every sound they heard, she played pure sound, and most bats didn’t fly away, just wiggle their ears.
This experiment raises more questions about how memory works in these bats and other animals, including the metabolic cost of memorization.
“I am 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 forget,” she explains. “But studying long-term memory is very difficult, because it takes a long time by definition. And testing memory in animals in captivity, while more convenient, is not necessarily representative of what animals can remember in the wild. She wants to return to the BatLab, run by STRI scientist and co-author Rachel Page, to find out more.
“STRI has been the basis of so much bat research. They’ve put together a large database of frog-eating bats, experiments done with bats, stimuli used, so if you catch a bat that’s been caught before, you already have everything its history. There are few places in the world where you can have so much detail,” she says. “I went from loving bats, but didn’t think they were very interesting, to realizing that they are very complex little creatures, with deep personalities and very engaging ways of interacting with the world.”
– This press release was originally posted on the Smithsonian Tropical Research Institute website