Human eyes, set as they are in front-facing sockets, give us a limited angle of view: we see what is directly in front of us, with only a few degrees of peripheral vision. But bats can broaden and narrow their 'visual field' by modulating the frequency of the squeaks they use to navigate and find prey, researchers in Denmark suggest today in Nature.
Bats find their way through the night by emitting sonar signals and using the echoes that return to them to create a map of their surroundings — a process called echolocation. Researchers have long known that small bats emit higher-frequency squeaks than larger bats, and most assumed that the difference arises because the smaller animals must catch smaller insects, from which low-frequency sound waves with long wavelengths do not reflect well.
That didn't sound right to Annemarie Surlykke, a neurobiologist who studies bat echolocation at the University of Southern Denmark in Odense. “When you look at the actual frequencies, small bats would be able to detect even the smallest prey they take with a much lower frequency,” she says. “So there must be another reason.”
Surlykke and her colleagues decided to test the hypothesis by studying six related species of bat that varied in size. They captured the animals in the wild and set them loose in a flight room — a pitch-dark netted corridor 2.5 metres high, 4.8 metres wide and 7 metres long, rigged on all sides with microphones and infrared cameras. “It’s a pretty confined space, so this corresponds to flying close to vegetation,” says Surlykke....
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