Bats 'tricked' into flying into buildings

From BBC - September 7, 2017

Modern buildings with large expanses of glass or mirrored surfaces are "potentially dangerous" for bats, research suggests.

Scientists are calling for monitoring of the risks, particularly in areas where bats congregate in large numbers.

Bats have a remarkable ability to fly at high speeds in the dark avoiding natural hazards such as trees.

Yet, smooth, vertical surfaces such as glass windows create a "blind spot" for the flying mammals, a study shows.

"Bats predominately rely on their echolocation system to forage, orientate, and navigate," says a team led by Dr Stefan Greif of the Max Planck Institute for Ornithology near Munich in Germany.

"We found that bats can mistake smooth, vertical surfaces as clear fight paths, repeatedly colliding with them, likely as a result of their acoustic mirror properties."

Collision risk

Bats use echolocation to detect obstacles in flight, find their way into roosts and forage for food.

As they fly, they make calls and listen to the returning echoes to build up a sonic map of their surroundings.

Bats can flit through natural obstacles, such as forests, which return some echo back to them.

However, vertical mirroring surfaces such as window panes appear to trick them into thinking that the way ahead is clear.

Prof Gareth Jones of Bristol University, who is not connected with the study, is an expert on bat echolocation.

"Sound reflects away in front of a bat flying over water, and the flight route ahead is often clear, or interrupted with obvious targets like trees that can be detected by echolocation," he explained.

"Vertical surfaces seem to reflect sound in ways that make the surface difficult to detect, and increase collision risk."

Smooth vertical surfaces are rare in bats' natural habitat. However, they treat horizontal, smooth surfaces like water, and attempt to drink from them.

To investigate the issue, researchers analysed the flight behaviour of greater mouse-eared bats (Myotis myotis) in dark flight tunnels.

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