Bats eavesdrop to learn to hunt

Close-up of a big brown bat catching a mealworm (Image: Genevieve Spanjer Wright) "Knowledgeable" bats had been trained to catch a mealworm that was hanging from a string

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Big brown bats learn to hunt by eavesdropping on the sonar of other bats, according to researchers.

A team from the University of Maryland, US, tracked bats as they flew around a room hunting for a mealworm suspended from the ceiling.

Young bats that flew with "experienced" bats - that had been trained to find the worm - were quickly able to find the treat alone.

The results are published in the journal Animal Behaviour.

They are the first to show that the bats (Eptesicus fuscus) actively attend to the sonar of others in order to learn from them.

This social learning is important to many mammals, but it had not been clearly demonstrated in bats.

Genevieve Spanjer Wright, a graduate student from the University of Maryland led the research.

She and her colleagues trained 12 "demonstrator bats" to catch a mealworm suspended from the ceiling by a string.

By repeatedly changing the location of the food item, the researchers trained the bats to actively hunt for it using their sonar or echolocation pulses.

Twenty-two young "naive" bats were then brought into the experiment. Eleven of them were allowed to fly around the same room with trained demonstrators that hunted for the mealworm. The other half flew around the room with untrained bats.

"When the naive bats then flew on their own, most of the animals that had previously flown with an experienced demonstrator knew how capture the mealworm," explained Dr Spanjer Wright.

"None of the ones that flew with an untrained bat captured the worm."

Social hunters

The team filmed the bats as they flew and then examined the bats' movements from successive frames of their grainy footage.

They realised that whenever an experienced bat found the worm and let out a "feeding buzz" - a very high frequency buzz that allows the animal to home in on its prey - the naive bat flew tucked in very closely to the demonstrator.

Dr Spanjer Wright said that, previously, it had not been known whether young, insect-eating bats learned socially to hunt.

"This is good evidence that they do," she said, "and it [shows] the mechanism by which the bats may learn - by increasing their interaction with a knowledgeable 'demonstrator' bat".

Dr Marc Holderied, a bat expert from Bristol University in the UK, said that many bat species tended to fly in small groups and that this had been interpreted as social learning.

"But," he said, "this experiment provides very convincing evidence that this species specifically looks at experienced foragers to learn how to forage."

He added that 50 million years of evolution had enabled bats to develop very advanced sonar that humans might even be able to copy if we study the animals behaviour carefully.

He told BBC Nature: "In the future, if we're teaching our robots to use echolocation, we need to watch what the bats are doing."

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