Bats build mental maps to recognise surroundings

Bats observe and remember echo templates to form mental maps of their environment, which helps them recognise their surroundings, a new study has found.
Bats have excellent spatial memory, and navigate with ease to important locations including roosts and foraging grounds, researchers said.
However, exactly how these mammals recognise such places through echolocation - perception based on soundwaves and their echoes - is largely unknown, they said.
New research from the University of Bristol in the UK and University of Antwerp in Belgium suggests that bats observe and remember templates to help form a cognitive map of their environment.
"When we visually recognise places, such as our living room or office, we identify and localise the various objects that make up the scene," said Marc Holderied from University of Bristol.

"Echolocation does not allow bats to do this, as the information it provides is more limited. We therefore wanted to discover how these animals recognise their locations differently to those with vision," said Holederied.

Researchers proposed that template-based place recognition might underlie sonar-based navigation in bats.
This would mean that the animals recognise places by remembering their echo signature, rather than their three-dimensional (3D) layout.
"The viability of a template-based approach to place recognition relies on two properties," said Dieter Vanderelst from University of Antwerp, who led the study as a research fellow at the University of Bristol.
"One of these is that templates must allow for unique classification in order for places to be recognisable. In other words, they must encode the bat's specific locations in space to allow it to recognise previously visited places," said Vanderelst.

To test their hypothesis, researchers built an 'artificial bat', a device which contained ultrasonic microphones and an ultrasonic speaker acting as ears and a mouth. Using this device, they collected a large number of echoes from three different locations.
Data was collected at the typical bat-flight heights of about two to three metres. Measurements from each site were gathered and stored by a computer integrated into the device.
Researchers then assessed the templates from the data and found that the echoes returning from each place were unique enough for them to be used to recognise the location.
"Importantly, our method used the echoes without inferring the location or identity of objects, such as plants and trees, at each site," said Vanderelst.

"In other words, the data support our hypothesis that bats can recognise places by remembering how they sound, rather than how they appear through the animals' 3D sonar imaging," he said.
The findings were published in the journal eLife.