A new study suggests that bats do not only locate their food through sounds but also track and predict where their prey is headed.
Researchers from Johns Hopkins University observed that bats create predictive models of their prey's movements on the fly. These models are supposedly robust and accurate that it can even track prey temporarily covered by obstacles like rocks or trees.
The details of the study are published in the journal Proceedings of the National Academy of Sciences, illustrating the use of hearing senses in prediction object motion paths. This predictive ability has been previously studied in sight before. But with hearing, understanding how bats do it could offer insights to support sight-impaired people in navigating their way through their environment.
Anticipation On-The-Fly, For Bats
"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," explains neuroscientist Cynthia F. Moss, senior author of the study and a Psychological and Brain sciences professor, in a press release. She adds that in a fast-moving environment where both the bat and the insect is flying, the bat would most likely miss its prey if it just relies on the latest echolocation data.
Researchers explained that the bat uses the time in-between echoes - or echolocation calls - to calculate just how far its prey is. Bats move their heads around to better adapt to the changing intensity of these calls, accurately determining the location of the prey in the horizontal plane. They then tested their hypothesis in the laboratory with an experimental setup that aimed to simulate a bat in the hunt. Researchers then trained the bats to stand on a perch and track insects in the enclosure - recording both the head movements and echolocation calls as the bats attempted to track the insects. The Johns Hopkins team also added obstacles for the echoes.
The Coordination Between Echolocation and Head Movements
"We devised mathematical models to test the data and we came up with different hypotheses of what the bats could be doing," said doctoral candidate Clarice Anna Diebold, co-first author of the study. The study argued that if the bat did not predict where the insect will be, the movement of its head will stay behind, lagging, compared to the target. Conversely, if the bat kept its head fixed, which sometimes occurred if the insect was in the same direction, it would disprove their hypothesis. Both cases did not hold true for the bats, which kept its head moving in prediction of the insect's location.
Lastly, if the bat only relied on its echolocation to estimate its prey's speed, it would not support the accuracy of the bats' tracking ability.
"We hypothesized that bats use both the velocity information from the timing of the echoes and further adjust their head aim," explained postdoc fellow Angeles Salles, co-first author of the study. She added that when they tested this particular model with the data they gathered, "it fit very well."
The new study contests the previously accepted understanding that bats do not predict where their insect prey will go - a conclusion from an old research in the 1980s, conducted before high-speed video recording was possible.
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