Bats use polarized light to navigate the sky, scientists have found.
In addition to echolocation — which only works for distances between 16 and 160 feet away — and an internal magnetic compass, researchers say that being able to follow the patterns of polarized light dispersed across the lower atmosphere help give bats a sense of directional orientation.
"We had already demonstrated that bats used a magnetic compass that was calibrated by cues observed at sunset," said study author Richard Holland of Queen's University Belfast, according to Wired
. "The question was, what cues? It was known that birds calibrate the magnetic field with the pattern of polarization at sunset, so we tried the same for bats."
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The Los Angeles Times reported
that while polarized light is mostly invisible to the naked human eye, some invertebrates, birds, and reptiles also use polarized light to calibrate their internal compasses. The study, published in the journal Nature Communications, is the first to show this ability in mammals.
In order to test bats' sensitivity to polarized light, researchers in Bulgaria put each of 70 adult female greater mouse-eared bats in a special box with windows. Some filters warped the natural polarization of the sky, while others left it intact. When they were freed at dusk, the bats exposed to the manipulated light flew off at 90 degree angles from their counterparts who were only exposed to natural light.
"Polarization doesn't give you a specific direction," like magnetic north does for many animals, said Stefan Greif of the Sensory Ecology Group at the Max Planck Institute for Ornithology in Germany, "so the bats who were confused disappeared either 90 degrees left or 90 degrees right."
The bats almost certainly readjusted once they had flown around for a bit, orienting themselves to the band of polarized light that emerges at dusk and consistently runs north to south. Generally speaking, polarized light occurs when rays from the sun become scattered by the atmosphere, making the light more directional.
It is still unknown what mechanism is responsible for the bats' ability to perceive polarized light, but researchers are looking forward to finding out. Insects have special photoreceptors in their eyes, giving them a somewhat dim view of polarized light, but the ability could be different in mammals.
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