Bats First Known Mammal To Use Dusk's Polarized Light To Set Their Compass
While bats are night creatures, who can maneuver around trees, chase insects and find their way home - all in the dark - they would still be lost without light, according to a new study.
Greater mouse-eared bats set their internal magnetic compass using the pattern of light polarization-light that vibrates in one direction-at dusk, according to the study, published Tuesday in the journal Nature Communications, writes National Geographic.
Without the proper light cues during that critical period, the bats become disoriented and have difficulty hard time finding their way home in the darkness.
This marks the first time a mammal has been documented making use of polarized light.
"We [humans] can perceive polarization if you know what to look for, but there is no functional meaning that we know of," study leader Stefan Greif, a biologist at Germany's Max Planck Institute, said in a statement.
This study, therefore, may 'shine a little light on how it works in humans as well.'
A drawback to bats' internal compasses is that the Earth's magnetic field varies across time and space, writes National Geographic.
To compensate for this, some animals calibrate their magnetic compass daily using more reliable geographic cues.
Prior studies have indicated that bats figure out what direction their magnetic compass is pointing using cues around sunset - however it was not clear how they managed to do this.
The study authors worked to a hypothesis: The flying mammals get directional information from polarized light.
At dusk, a strong band of polarized light that runs like a rainbow from north to south. This phenomenon that provides a consistent geographic reference and is a known orientation cue for birds, writes National Geographic.
This light pattern occurs as polarization is maximized when the sun's rays scatter at a 90-degree angle from their original path.
Greif and his colleagues tested the role of polarized light by experimentally manipulating 70 greater mouse-eared bats in Bulgaria, writes National Geographic.
The team placed each bat in a box that simulated polarized light at sunset - some bats saw the natural pattern while others saw a band of polarization that was rotated 90 degrees.
The researchers then displaced the radio-tagged bats more than 14 miles (20 kilometers) from their roosting cave and tracked their movements in the night, writes National Geographic.
They found that the bats shown the altered polarization pattern did not seem to know what direction was home.
In fact, many of these bats went in directions that were rotated 90 degrees from the correct orientation, as would be expected if they were navigating using a polarization-calibrated magnetic compass, writes National Geographic.
The fact that bats 'use the exact same compass calibration method [as birds] is remarkable' Rachel Muheim, an expert on bird navigation at Sweden's Lund University, said in an email to National Geographic.
It 'may indicate that other organisms do the same,' said Muheim, who wasn't involved in the research.