Bats ‘can predict the future’, study of hunting technique reveals

Advanced echolocation techniques allow bats to build ‘on-the-fly predictive models’ of where insects are going

Harry Cockburn
Tuesday 03 November 2020 09:10
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A mouse-eared bat carries off a meal. Bats don’t just aim at where their prey is, but where they think it’s going to be
A mouse-eared bat carries off a meal. Bats don’t just aim at where their prey is, but where they think it’s going to be

Bats are extraordinary animals — they are the only truly flying mammal, and they are so adept at it that they can outmanoeuvre birds. They also pollinate plants, use echolocation like sonar to navigate through the darkest nights, are known to trade food for sex, and even know to self-isolate when they get ill.

But the latest scientific research into bats reveals these matchless mammals are such highly evolved creatures, they can accurately “predict the future”, when it comes to tracking their prey.

So, while their oracular abilities may not be much use in a casino, bats are very skilled at predicting one thing — where to find dinner.

Bats calculate exactly where their prey is going by building on-the-fly predictive models from echoes.

Researchers from John Hopkins University in Maryland said the bats’ predictive models are so robust, they can continue to track their airborne prey even when it temporarily vanishes behind echo-blocking obstacles like trees.

The researchers said that while the prediction of possible paths based on visual information has been extensively studied, their project is the first to do so using auditory information.

The team said their work could help scientists gain greater insights into auditory-guided behaviours among humans and other animals, including sight-impaired people who use sounds to track objects around them.

“Just the way a tennis player needs to find out when and where they will hit the ball, a bat needs to anticipate when and where it will make contact with the insect it's hunting,” said senior author Cynthia Moss, a neuroscientist and professor of psychological and brain sciences at John Hopkins University.

“The insect is flying. The bat is also flying. In this very rapidly changing environment, if the bat were to just rely on the information it got from the most recent echo, it would miss the insect.”

Bats use the time delays between each echolocation call and the resulting echoes to determine how far away prey is.

The researchers said the bats tilt their heads to catch the changing intensity of echoes to figure out where the prey is in the horizontal plane. They then must put together echo information about object distance and its direction to successfully track an erratic moving insect.

But because the bats are so adept at this, the research team wondered whether in addition, the bats could also be somehow using this information to predict where their prey is going.

To test this in the lab, they designed an experiment that closely mirrored the situation of a bat hunting in the wild.

They trained bats to stay on a perch and track insects. The team recorded each bat's echolocation calls and head movements as they changed where the insects moved and how quickly.

They also added obstacles to interrupt the echoes.

“We devised mathematical models to test the data and we came up with different hypotheses of what the bats could be doing,” said co-first author Clarice Anna Diebold, a doctoral candidate in psychological and brain sciences.

If the bats were not predicting where the insects were going, then their head movements would always lag behind the target.

But the scientists found that wasn't the case.

And if the bat kept his head in a fixed position, which sometimes reflected where the insect ended up, that would eliminate the prediction theory.

But that wasn't happening either. And if the bat was only using information from the echoes to estimate velocity, that wouldn't be enough to explain the extent of the bat's precision.

“We hypothesised that bats use both the velocity information from the timing of the echoes and further adjust their head aim,” said co-first author Angeles Salles, a postdoctoral fellow.

“When we tested this model with our data, we saw it fit very well.”

The findings upend the previous accepted notion that bats do not predict an insect's future position — a conclusion largely drawn from a 1980s study done before high-speed video was widely available.

“The question of prediction is important because an animal must plan ahead to decide what it's going to do next,” said Dr Salles.

“A visual animal or a human has a stream of information coming in, but for bats it's remarkable because they're doing this with only brief acoustic snapshots.”

The research is published in the journal Proceedings of the National Academy of Sciences.

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