Bats can recognise each other's echolocation calls, study shows
Bats are able to recognise other individuals by their echolocation voice, new EU-funded research reveals. The findings are important because little is known about how small groups of bats stick together while flying in the dark at high speeds, or avoid interference of their echolocation signals, for example. The study, published in the journal PLoS Computational Biology, received EU support through the PASCAL ('Pattern analysis, statistical modelling and computational learning') and PERACT ('Perception and action in space') projects, which were funded under the 'Information society technologies' (IST) and 'Human resources and mobility' budget lines respectively of the Sixth Framework Programme (FP6). Vocalisations are mostly used for communication, but they can also convey information about an individual's identity, gender, health and behaviour. Recent research has revealed that just like humans, many animals, including some bats, are able to recognise other individuals on the basis of their social vocalisations. However, in addition to their social vocalisations, bats also emit a constant stream of echolocation calls; they analyse the echoes of these calls to make out their surroundings. In this latest study, the scientists discovered that greater mouse-eared bats (Myotis myotis) can distinguish between different individuals on the basis of their echolocation calls alone, even though the primary purpose of these calls is not communication. Furthermore, the sound of an individual's echolocation voice varies according to the task it is carrying out, making the bats' ability to recognise one another even more remarkable. The researchers then developed a computer model that replicates the way the bats analyse each other's voices. 'Our model suggests that the bats learn the average calls of other individuals and recognise individuals by comparing their calls with the learnt average representations,' the scientists write. 'An extremely over-simplified classification rule could be: 'The call with lower energy at approximately 65 kHz and higher energy at approximately 45 kHz belongs to Bat 3.',' the researchers explain. The authors conclude that: 'despite their high variability, broadband bat-echolocation calls contain individual-specific information that is sufficient for recognition.'
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