Twin siblings sound alike: isolation call variation in the noctule bat, Nyctalus noctula

Abstract

We studied the individual variation in bat pups' isolation calls in the noctule bat, one of the few bat species in which twin births are common. Based on discriminant function analyses we showed that pups' isolation calls were individually distinct and therefore likely to bear vocal signatures suitable for acoustically mediated mother–offspring recognition. The comparison of individual variation of isolation calls in intratwin and intertwin pairs revealed that isolation calls of twin siblings were more similar to the calls of each other than to the isolation calls of unrelated pups of the same age. Therefore, isolation calls may not only encode individual identity but also affiliation to a certain social group (e.g. twin pairs). The distinctiveness of isolation calls increased with the age of the pups and calls of twin siblings remained similar to each other as the pups got older, whereas the calls of unrelated pups diverged, suggesting that vocal signatures become more distinct during ontogeny and that the similarity of twin siblings' isolation calls is persistent over time.