Bats were shown to use the pattern of polarized light in the sky for orientation and navigation in a recent study. The study showed that, at sunset, which is when bats are especially happy to fly around, they calibrate their internal “magnetic compass” using polarized light. By resetting this internal compass, they can adjust their orientation.
Polarization of light refers to the spatial orientation of the light waves. Light comes in various wavelengths, which are related to color vision, but the waves of light can also have a particular orientation in space, such as up or down or sideways. When light is polarized it means that the orientation of the waveforms is all in one direction, rather than in all or many directions. In simpler words, it means that all the “bumps” in the waves of light are going up and down, for example, rather than left and right.
While it has been shown previously that birds, fishes and reptiles use the pattern of polarized light in the sky to navigate, this was the first study to show a mammal used the pattern of polarized light in the sky as well. At sunset, a band of polarized light appears in the sky with an orientation going north and south. This is what the bats use to calibrate their internal compass. It is well known that bats sleep during the day and wake up at sunset to fly around at night.
The experimental design for the study was to have the bats housed in boxes to watch the sunset. Some of the bats looked out at the sky normally and other bats could only look at the sky from the box through a lens that rotated the polarization of the light 90 degrees. When the bats were let out of the boxes, the bats that had to look through the polarizing lens started to fly home at 90 degrees in the wrong direction.
This study on bats that showed they use polarized light for orientation was carried out by researchers at Queen’s University Belfast in the United Kingdom, the Max Planck Institute for Omithology at Eberhard-Gwinner-Strabe in Germany and the Department of Zoology at the University of Tel Aviv in Israel. Dr. Stefan Greif was the lead scientist. The study report was published in Nature Communications.
The next step in this research would be to identify the sensory receptor for polarized light in bats. Researchers will likely look at receptors in the visual system as an initial step in identifying how information about polarized light is received and then subsequently analyzed by the nervous system. People often speak of being blind as a bat but bats are really not blind. They have a visual system and have visual perceptions. What is special about bat vision is it is extremely sensitive relative to the vision capabilities of other animals. Bats can see at very low light levels, whereas humans cannot.
Bats also have another type of sensory system that allows them to navigate. They can do echolocation. This means they can emit soundwaves and then sense their reflection from objects. Their sense of echolocation, however, only works for distances of about 50 meters. Use of polarized light to orient and navigate allows bats to perceive what is in their environment at much greater distances.
By Margaret Lutze