Bats calculate where their prey is headed by building on-the-fly predictive models of target motion from echoes, US researchers have found.
They use the time delay between each echolocation call and the resulting echoes to determine how far away prey is, and tilt their heads to catch the changing intensity of echoes to figure out where it is in the horizontal plane, according to a paper in the journal PNAS.
And the process is robust enough to keep working even when the prey vanishes behind echo-blocking obstacles like trees.
“[A] bat needs to anticipate when and where it will make contact with the insect it’s hunting,” says senior author Cynthia F Moss, a neuroscientist at Johns 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.”
To test this, Moss and colleagues trained bats to stay on a perch and track insects then recorded their echolocation calls and tracked their head movements as they changed where the insects moved and how quickly. They also added obstacles that interrupted the echoes.
They quantified the direction of the bat’s head/sonar beam aim and echolocation call rate as it tracked a target that moved across its sonar field then applied mathematical models to differentiate between non-predictive and predictive tracking behaviours.
Their findings, they say, 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.
And they apply to any animals that track moving sounds, and even to people, such as the vision impaired who use clicks and cane taps to help navigate while avoiding obstacles.
“The question of prediction is important because an animal must plan ahead to decide what it’s going to do next,” said co-first author Angela 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.”