The Greater mouse-eared bat (Myotis myotis) is the first mammal that’s known to use polarization patterns in the sky to calibrate an internal magnetic compass, according to a team of scientists led by Dr Richard Holland of Queen’s University Belfast. Despite this discovery, the team has no idea how the bat manages to detect polarized light.
The Greater mouse-eared bat (Myotis myotis) is an European species of bat in the Vespertilionidae family.
Polarization patterns depend on where the Sun is in the sky. They are clearest in a strip across the sky 90 degrees from the position of the Sun at sunset or sunrise.
But animals can still see the patterns long after sunset. This means they can orient themselves even when they can’t see the Sun, including when it’s cloudy.
Many creatures including bees, anchovies, birds, reptiles and amphibians, use the patterns as a compass to work out which way is north, south, east and west.
“Most people are familiar with bats using echolocation to get around. But that only works up to about 50 m, so we knew they had to be using another of their senses for longer range navigation,” said Dr Stefan Greif of Queen’s University Belfast, who is the first author of the study published in the journal Nature Communications.
In their study, Dr Holland, Dr Greif and their colleagues showed 70 adult, female mouse-eared bats one of two different types of polarization patterns at sunset.
The scientists then took them to one of two release sites in Bulgaria about 20 to 25 km from their home roost.
They released the bats at night, when no polarization is visible, and followed the direction they set off in using small radio transmitters attached to their backs.
They found the bats that had been shown a shifted pattern of polarized light headed off in a direction shifted at right angles from the controls released at the same time.
Bats probably use a suite of senses, including the position of the Sun or the stars, the Earth’s magnetic field, smells, sight, and of course, echolocation to navigate, according to the scientists.
“Anything we can do to understand how they get about, how they move and navigate will be step forward in helping to protect them,” Dr Holland said.
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Stefan Greif et al. 2014. A functional role of the sky’s polarization pattern for orientation in the greater mouse-eared bat. Nature Communications 5, article number: 4488; doi: 10.1038/ncomms5488
