How bats use a compass to find their way at night

A European bat type can use the scatter patterns of sunlight to program its internal compass for hunting after dark - the first mammal known to do so, researchers said last week.

The only flying mammals, bats use echolocation, a form of sonar, to find their way around, but this only works at distances up to about 50 meters.

They leave their roosts in caves, trees and buildings at night to hunt for insects, often ranging hundreds of kilometers and returning before sunrise to avoid predators.

"We knew they had to be using another of their senses for longer-range navigation," says Stefan Greif of Queen's University Belfast, co-author of a study published in the journal Nature Communications.

Scientists have long wondered whether bats could read the pattern of sunlight scattered in the atmosphere (polarization) to orient themselves to Earth's magnetic field.

These patterns depend on where the sun is in the sky, and are used by insects, birds, fish, amphibians and reptiles in navigation.

For the study, a team of biologists captured 70 female greater mouse-eared bats in Bulgaria and placed them in see-through cages at a site 1.3 km from their cave.