Some bats can travel very long distances when foraging and migrating between breeding and wintering grounds. A Nathusius’ pipistrelle recently flew more than 600km from Somerset to Holland, for instance, and several European species, such as the greater noctule, can cover more than 1,000km.
How bats safely navigate over these long distances used to be something of a mystery – vision and echolocation are less useful on long migration routes. We now know that bats, in common with many birds, insects and fish, can detect the direction of the Earth’s magnetic field, through iron oxide particles (magnetite) in their cells. This internal ‘compass sense’ is a vital navigation aid, but in order for it to be used effectively, it needs to be calibrated against other navigational cues.
Recent studies on greater mouse-eared bats have found that at sunset the animals use the pattern of polarised light as a clue, even when the sun is obscured by clouds. They are the first mammal species ever recorded to do this. However, how the bats detect the polarised light is as yet unknown.
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