Scientists have discovered that bats use polarization of the setting sun to orient their internal magnetic compasses before setting out to hunt in the dark.
According to the new study, published in the journal Nature Communications, birds are known to use the pattern of polarized light in the sky to help them calibrate their compass mechanism, reports Science Recorder.
Other orienting and navigation mechanisms animals use include the position of the sun or stars, strength and inclination of the Earth’s magnetic field, and olfactory cues.
Even though bats are known to use echolocation to home in on their prey, this mechanism only works at distances up to a maximum of about 165 feet. For longer distance navigation, bats must use some other sensory input, such as vision.
The pattern of polarized light from the sun is strongest at dusk and dawn, when a strip of polarized light arches over the sky with one end pointing north and the other pointing south.
The researchers decided to test the hypothesis that bats calibrate a magnetic compass with cues from this polarization pattern.
To do this, they conducted experiments with 70 female greater mouse-eared bats by taking them from their home cave and allowing them to observe the sky at sunset from inside experimental boxes.
The boxes were fitted with different light filters to manipulate the sun’s polarization pattern.
Then, when the bats were released from more than 12 miles away, they attempted to head home, according to the Christian Science Monitor. A control group flew in the right direction, but experimental groups flew either 90 degrees to the left or 90 degrees to the right, depending on the type of box filter they had been confined in during sunset.
The scientists concluded that the polarization pattern of the sun provides a more reliable calibration point for the bats than the sun’s position in the sky.
That way, even when the sun is obscured by clouds, polarization can still give accurate information.
In addition, polarization patterns are visible long after the sun has set, when the bats emerge from their caves to hunt.