A study demonstrating that the female greater mouse-eared bat uses polarised light for orientation is reported in this week in Nature Communications. This renders bats the only mammal known so far to make use of the polarisation pattern in the sky.

When animals orient and navigate, they rely on a variety of sensory information such as the position of the sun or stars, strength and inclination of the Earth’s magnetic field, or the pattern of polarised light in the sky. To achieve the greatest accuracy these different systems need to be calibrated against one another. The use of polarisation as an orientation cue is known from invertebrates and birds but has not previously been demonstrated in mammals.

Stefan Greif, Richard Holland and colleagues used translocation experiments to demonstrate that the female greater mouse-eared bat, Myotis myotis, uses polarisation cues at sunset to calibrate a magnetic compass. The experiments involved 70 adult female bats that observed the sky at sunset from experimental boxes, in different locations, equipped with different filters to manipulate the polarisation pattern of sunlight. The bats were then observed to use the polarised light for orientation to travel back to their cave.

While this study has implications for the sensory biology of mammalian vision, it is currently unclear how exactly bats perceive and use the sky’s polarisation pattern.