Bats can remember sounds they haven’t heard for years

Animals known to be highly intelligent, such as ravens and chimpanzees, have good long-term memory – and now it seems that some bats do too.

WHEN fringe-lipped bats learn the sound of a dinner bell, they remember it for years.

The bats’ enduring memory is comparable to that of other animals renowned for their expansive cognitive skills, such as crows and primates.

Fringe-lipped bats (Trachops cirrhosus) are native to rainforests in the Central and South American tropics. They are nocturnal predators with a broad diet, snatching up insects, frogs, lizards and small mammals. The bats have a keen ear and are able to discern between the calls of poisonous and non-poisonous prey.

To see how long this ability sticks around, a team led by May Dixon at The Ohio State University in Columbus took some bats to school.

Dixon and her colleagues captured 49 fringe-lipped bats between 2010 and 2018 in Panama’s Soberanía National Park. In a flight cage, the researchers trained the bats to respond to recordings of frog calls coming from a speaker by giving them pieces of fish when the noise played.

They then played a mix of frog calls and mobile phone ringtones, incrementally reducing the frog call volume and increasing the ringtone volume until the bats were trained to attack the pure ringtone sounds.

The team then taught the bats to discriminate between ringtones, providing a tasty reward for some sounds and giving them nothing when others played.

They were released into the wild, and eight of them were recaptured between 1 and 4.2 years later. When they were played their food-associated ringtones from training, all eight of the recaptured bats approached the speaker and six of them attacked it. When the researchers repeated this with 17 wild bats that hadn’t received the training, only one approached the speaker (bioRxiv, doi.org/hnzn).

The researchers note that remembering auditory information for 4.2 years is in line with recall in highly intelligent animals: ravens have been shown to retain knowledge of past social relationships for three years, and chimpanzees can remember how to solve a food-gathering puzzle for three years.

They suggest that a long and detailed memory may be useful to fringe-lipped bats, allowing them to recognise and exploit prey animals that are rare or seasonal, so aren’t encountered for extended periods.

Jesús Rafael Hernández-Montero at the ECOSUR San Cristobal research centre in Mexico is impressed by the bats’ robust recall. “They get this association in a very short period of time, within 11 to 27 days of training,” he says.

“And then they’re able to remember that 4.2 years later, so that’s quite amazing.”

He points out that, years later, the bats also responded to unrewarded ringtones from their training. Generalising the ringtone-food association may reflect curiosity, perhaps making them “more prone to explore new cues”, he says, which would potentially improve their success at hunting.

In general, bats may be encouraged to evolve long, rich memories on account of their biology and lifestyle, says Hernández-Montero. They can live for 20 years or more, group together in complex societies and navigate complicated environments in complete darkness – all traits aided by the long-term logging of social and environmental data.

Vladimir Pravosudov at the University of Nevada, Reno, isn’t surprised by the findings. “It’s cool that they found [a long memory in the bats],” he says.

But he also notes that “there’s lots of data suggesting that a lot of animals remember things for a long time”.

One lesson emerging from these and other recent findings is that impressive cognitive traits are actually widespread across the animal tree of life, says Pravosudov. Even fish and invertebrates commonly have lengthy memories and substantial cognitive prowess.

The fact is here : Bats can remember sounds they haven't heard for more than 4 years