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The shape of sound: elliptic Fourier descriptors (EFD) discriminate the echolocation calls of Myotis bats (M. daubentonii, M. nattereri & M. mystacinus)

Mathieu Lundy, Emma Teeling, Emma Boston, David Scott, Daniel Buckley, Paulo Prodohl, Ferdia Marnell & Ian Montgomery (2011). The shape of sound: elliptic Fourier descriptors (EFD) discriminate the echolocation calls of Myotis bats (M. daubentonii, M. nattereri & M. mystacinus). Bioacoustics, Volume 20 (2): 101 -116

 

Abstract: 

Bats of the genus Myotis cannot be identified reliably using conventional acoustic analyses. Here we use morphology of echolocation calls to discriminate between Myotis spp. This method may be used to identify unknown roosts to species level in the field. Echolocation calls of M. daubentonii, M. mystacinus and M. nattereri, were recorded in emergence flights from roosts. Images of echolocation calls were extracted for morphological analysis performed in SHAPE, a program that transforms twodimensional outline data into Elliptic Fourier Descriptors. Species typical call shapes were described with Mahalanobis models. Discriminant Function Analyses (DFA) were applied with Mahalanobis scores of typical shape alone and with a spectral call parameter, maximum frequency. DFA achieved an overall correct classification rate of 88.9% using typical outline shapes alone. Correct classification of 100% of both M. daubentonii and M. mystacinus was achieved by both typical call outlines. For M. nattereri, 79.6% of calls were correctly classified by call morphology, but the addition of maximum frequency improved this to 96.3%. Shape analyses provide a quick and easy method of distinguishing Myotis species under field conditions and could be extended to include other species of bats that share conventional acoustic parameters.

Keywords: 
Chiroptera, echolocation, Elliptic Fourier Descriptors, morphometrics, ultrasound.