The fringed-lipped bat, weighing less than 40 grams, appears to have an elephant memory. And that has also taken scientists by surprise.

To find out more about the memory of wild fringe-lipped bats, American researchers set up a sophisticated experiment. They let the bats hear a very attractive sound through speakers, namely the cry of their favorite meal: the tungar frog. When the bats came to that sound, they were rewarded with a tasty snack that hung above the speakers. Over time, the sound of that tungar frog was mixed with and eventually even completely replaced by a ringtone. The reward that the bats received when they flew to the speakers remained the same.

Goodbye

Then the researchers introduced three other ringtones; when these sounded, there was no reward for the bats, and the animals quickly realized it; they did not fly to the speaker when they heard those three ringtones. With that, the experiment came to an end. The researchers microchiped the wild bats that had participated in the experiment and released them.

Eight old acquaintances

A year later – and in the three years after that – the researchers caught bats in the same area. Eight of them turned out to be microchipped and thus former participants in the experiment. The researchers let these bats hear the ringtone that was previously accompanied by a reward. All the bats then headed for the sound and six of them actually landed the reward waiting there, clearly indicating that they expected food to be found there.

A control group, consisting of 17 wild bats that had not participated in the experiment one to four years earlier and were therefore also unaware of the association between the ringtone and a tasty snack, listened to the ringtone almost unmoved in the meantime. They pricked up their ears a little, but didn’t fly toward the sounds.

Surprising

The findings are surprising, said researcher May Dixon. The scientists hadn’t anticipated that some of the bats could remember the ringtone for up to four years. “I was surprised,” Dixon says. “When I got into this, I thought it would be reasonable — also given all the other stuff they need to know and the fact that long-term memory is pretty precious — that they’d remember the ringtone for at least a year. Four years is a really long time, especially for a sound you may never hear again.”

Valuable research
The research is very valuable, says Dixon. “The study taught us a lot, because relatively few studies have been done on the long-term memory of wild animals.” In their study, Dixon and colleagues cite some 39 previous studies on animal memory. In addition, the memory of dolphins (they can remember things for up to 20 years) and that of turtles and sea lions (which can remember things for up to 9 and 10 years respectively) stand out. But all these studies are based on experiments with animals in captivity. “Studying memory in the wild is important,” said researcher Gerald Carter. “You can’t necessarily extrapolate the great wealth of data we have about lab animals to what congeners do in the wild, a place where they have to remember so much more. When it comes to captive versus wild animals, both the environment and the brain are different.”

Good memory: always beneficial?

Another species with quite impressive long-term memory is, of course, humans. And we tend to view that long-term memory as a big advantage, something that makes us much more intelligent than other species. But whether an extremely strong long-term memory is always beneficial for (wild) animals is very doubtful. “It’s not always that being the smartest or having the best memory is an advantage,” Dixon said. For example, research in which fruit flies were bred in such a way that they developed a better memory often lost out to their ‘ordinary’ counterparts. “Just because it’s helpful for humans to be so smart and have such a good memory doesn’t mean it’s best for other animals. That is why we want to find out when these skills really help or hinder animals.”

To this end, for example, the researchers intend to experiment with other bat species in the future. In this way, it is hoped that it will be possible to determine which species are and which are not blessed with an impressive long-term memory and under what circumstances such long-term memory evolves and is therefore advantageous.