Belfast Telegraph

Bats' light-nav system revealed

Fresh evidence has emerged of the sophisticated navigational skills of bats with new research showing they use polarised light to help them make their way around at night.

Greater mouse-eared bats were shown to react to the way the sun's light is scattered in the atmosphere at sunset in order to calibrate their internal magnetic compass, in a study published in the journal Nature Communications.

Researchers said a huge number of animals including bees, dung beetles and fish use this system as a form of compass, but bats are the first mammals to do so. They said they remained baffled as to how bats achieve this feat.

The finding adds to a growing list of systems used by bats to navigate including echolocation or sonar, the sun, stars and the Earth's magnetic field, as well as smells and sight.

'"Every night through the spring, summer and autumn, bats leave their roosts in caves, trees and buildings to search for insect prey.

"They might range hundreds of kilometres in a night, but return to their roosts before sunrise to avoid predators. But, until now, how they achieved such feats of navigation wasn't clear," Stefan Greif of Queen's University Belfast, lead author of the study, said.

"'Most people are familiar with bats using echolocation to get around. But that only works up to about 50 metres (164ft), so we knew they had to be using another of their senses for longer-range navigation."

In the experiment, scientists showed 70 adult, female mouse-eared bats one of two different types of polarisation patterns at sunset.

They then released them in Bulgaria around 20 to 25 kilometres (12-15 miles) from their home roost in the early hours of the morning, when no polarisation was visible.

The bats that had been shown a shifted pattern of polarised light headed off in a direction at right angles from those that had not.

Dr Richard Holland, of Queen's University, and co-author of the report, said the findings would contribute to efforts to stem the decline of bat species across Europe. He said wind turbines were seriously harming their populations.

"We know that bats must be 'seeing' the turbines, but it seems that the air pressure patterns around working turbines give the bats what's akin to the bends," he said.

'"It's most common in migratory species, with around 300,000 bats affected every year in Europe alone. You just find bats dead at the bottom of these turbines. One option is to reduce turbine activity during times of peak migration."

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