The windows were covered with light-polarizing filters - some of them oriented so the bats were exposed to "natural" scatter patterns and others tilted at a 90-degree angle.

The bats were offered a clear view of the horizon and the sun around dusk, when the scatter pattern is strongest, and then taken to two sites over 20 km away from where they were released on different nights, fitted with radio-transmitters.

Trying to make their way home, the two groups flew in different directions, with more of those exposed to the natural patterns approaching the target.

"The sunset could have been used as a cue to incorporate this information, but apparently bats ignored this and weighed the polarization cue higher," the study authors conclude.

It is not known, however, how the bats manage this feat. Other animals which use polarization patterns have special eye adaptations.

Animals rely on a range of sensory information for navigation - the position of the sun or stars, the Earth's magnetic field, smells, visual cues and light-scatter patterns.

These inputs have to be calibrated against one another for the most accurate result.

Bats, which are natural pest controllers, are in decline across Europe.

"Anything we can do to understand how they get about, how they move and navigate will be a step forward in helping to protect them," fellow researcher Richard Holland says in a statement.