Tools for the computation of acoustic parameters of narrow band high frequency clicks of odontocetes

Acoustic recording can be a very interesting way of monitoring cetaceans for conservation purposes. However, some sympatric species produce very similar sounds and are thus difficult to study specifically. In this work, we are interested in characterizing the narrow band high frequency (NBHF) clicks emitted by several species of odontocetes, among which all porpoises and some species of dolphins. The traditional acoustic parameters (durations, frequencies, bandwidths) of NBHF clicks show several drawbacks, such as redundancy, lack of precise definition, and poor robustness to noise. In this study, we propose a new method of characterizing NBHF clicks by fitting a Gabor wavelet to the signal and thus extracting two specific metrics, the Gabor frequency and the Gabor duration. We first assess the theoretical usefulness of this mathematical model, and then test it against traditional measurements in numerical examples with varying levels of noise. Our method is then applied to two empirical datasets recorded in South America, a place were many sympatric species are found to emit NBHF clicks. Two large sets of signals are thus analyzed and compared : one of clicks of Peale’s dolphins (Cephalorhynchus australis) from Chaihuin bay, Chile, and the other of clicks of Franciscana dolphins (Pontoporia blainvillei) from San Clemente del Tuyu, Argentina. Our metrics allow a good characterization of each species’ clicks with quick and efficient computation, with good reproducibility across different recording devices, and a clear separation of the two species. We suggest it could be applied to more datasets from different species, and possibly be used to classify NBHF of sympatric species.