The problem of intercepting a single bat in a dense swarm is solved by hunting hawks. Our understanding of how a predator selects and tracks a target has increased.
A post-doc with the Oxford Flight Group in the Department of Biology at the University of Oxford was involved in the research. The bats emerged from a cave each evening and were observed by the researchers. Using an array of cameras, they were able to reconstruct the flight trajectory of the animals.
Being in a large group, such as a school of fish or a swarm of bats, is thought to provide protection from predatory animals. As the group size of the prey increases, they should be less successful at catching prey. There is mixed evidence on the effects of confusion.
The researchers went to a remote site in New Mexico to understand more about the confusion effect. The bats fly out in a ribbon at dusk. It's an excellent study system because of its predictability.
Two cameras were used to film hawks hunting the bats. The flight paths of the hawks were reconstructed in 3D and compared to the flight paths of the real birds.
The hawks would steer towards a fixed point instead of continuously targeting a single bat. The question of how the hawks chose which targets to grab remains. The hawks may use this to single out a target bat from the swarm as any bat on a collision course with the hawk would appear to remain on a constant basis. Dr.Brighton gives an explanation.
The swarm appears to move erratically from the viewpoint of a person standing on the ground. Any bat that is on a collision course with another bat will appear stationary against the background.
The strategy of targeting a fixed point in a group of prey may be a more general mechanism yet to be discovered in other predator. It may only work if prey aggregations are dense.
"Our work shows how the appearance of a swarm depends on the predator's own motion, so starling murmurations and many other group behaviors that look bewildered to our own eyes may not appear so confusing to a predator taking the plunge," said Professor Graham Taylor. The same will be true for other agents who use visual targeting of swarms.
The paper is titled "Raptors avoid the confusion effect by targeting fixed points in dense aerial prey aggregations."
More information: Caroline Brighton, Raptors avoid the confusion effect by targeting fixed points in dense aerial prey aggregations, Nature Communications (2022). DOI: 10.1038/s41467-022-32354-5. www.nature.com/articles/s41467-022-32354-5 Journal information: Nature Communications
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