In new research, a team of researchers from Ohio State University has introduced 49 frog-eating bats with a series of ringtones that caught their attention and trained them to associate flying against only one of the tones with a reward: a baitfish snack. Between one and four years later, 8 of these bats were recaptured and re-exposed to the food-related ringtone. Everyone flew towards the sound, and 6 flew all the way to the speaker and took the food reward, which means they expected to find food.
“I was surprised! I thought at least a year would be a reasonable time for them to remember, given all the other things they need to know and given that long-term memory has real costs,” I say. Dr. May Dixona postdoctoral fellow at Ohio State University.
“Four years feels like a long time to hold on to a sound you may never hear again.”
In his study, Dr. Dixon and colleagues revealed wildcats bats with fringed lips (Trachops cirrhosus) to a very attractive sound in the lab: the male’s mating cry túngara groda (Engystomops pustulosus)one of this species’ preferred prey for bats.
Flying to that sound was rewarded with a piece of bait fish placed on the mesh above the speaker.
Over time, the sound was mixed up and gradually replaced by a ringtone, but the rewards were the same.
The researchers then introduced three other ringtones, none of which were linked to a food reward.
Bats were trained to distinguish the differences and eventually no longer flew towards the unrewarded sounds.
Each bat secured at least 40 snacks by flying to the trained ringtone for 11 to 27 days.
All bats were microchipped and returned to the wild.
Starting a year later and for another three years, the team caught bats and identified eight from the first attempt with their microchips.
In a follow-up test of their response to the original rewarded ringtone, all eight trained bats quickly flew to the sound and could see the difference between that ringtone and a new, steady tone, although many of the bats flew to an unrewarded sound from the initial training.
When 17 untrained bats were exposed to these sounds, they jerked most in response to the sounds, but did not fly towards them.
“The study taught us a lot because there are relatively few studies of long-term memory in wild animals and we do not have a systematic understanding of long-term memories in nature yet,” said Dr. Dixon.
“If we can gather additional data on different species of bats, we can take this apart and see what life stories choose for long memories.”
Despite the human tendency to assume that a long memory gives our species the intelligence advantage, nature shows us that memory flexibility – also called adaptive forgetting – can be important for survival.
“It’s not always true that it is actually beneficial to be the smartest or have the longest memory,” said Dr. Dixon.
“Research has shown that fruit flies selected for improved memories can not compete as well with other fruit flies.”
“Just because it’s useful for humans to be so smart and have such good memories, does not necessarily mean it will be the best for other animals.”
“That’s why we want to find out when these skills will actually help animals and when they can be a responsibility.”
M. May Dixon et al. 2022. Long-term memory in frog-eating bats. Current biology 32 (12): 557-558; doi: 10.1016 / j.cub.2022.05.031
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