Bats build mental maps to recognise surroundings

London: Bats observe and remember surroundings to form a mental map of their environment which, with their excellent spatial memory, enables them to navigate with ease to important locations including roosts and foraging grounds, says a study.

The study proposes that template-based place recognition might underlie the sonar-based navigation known as echolocation that bats usually are known to use for navigating and finding food in the dark. 

This would mean that the animals recognise places by remembering their echo signature, rather than their three-dimensional (3D) layout, the researchers said.

"The viability of a template-based approach to place recognition relies on two properties. One of these is that templates must allow for unique classification in order for places to be recognisable," said lead author Dieter Vanderelst, from the University of Antwerp in Belgium, who led the study as a research fellow at the University of Bristol in Britain.

"In other words, they must encode the bat's specific locations in space to allow it to recognise previously visited places," Vanderelst added.

To test their hypothesis, the team built an 'artificial bat', a device which contained ultrasonic microphones and an ultrasonic speaker acting as ears and mouth. 

Using this device, the researchers collected a large number of echoes from three different locations.

Data were collected along typical bat-flight heights of about two to three metres. Measurements from each location was gathered and stored by a computer integrated into the device. 

The team 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.

"Our method used the echoes without inferring the location or identity of objects, such as plants and trees, at each site," Vanderelst said.

The findings showed that bats can recognise places by remembering how they sound, rather than how they appear through the animals' 3D sonar imaging.

Further, the use of prominent landmarks might be an emergent feature of template-based place recognition.

"The prominence of a template's catchment area reflects how likely it is that the template will be observed and stored in a map during exploration suggesting that bats could use boulders as landmarks for mapping," Vanderelst explained, in the paper published in the journal eLife.

"This leads us to believe that cognitive mapping based on templates would show a natural preference to use such landmarks, as they return stronger and more recognisable echo signatures," Vanderelst concluded.