Maintaining of low Doppler shifts in cetaceans as strategy to avoid predation.

Abstract: Cetaceans are widely diversified in their sonometric characteristics but no comparative research has determined the general patterns that condition their bio-acoustic evolution across a large number of species. Echolocation calls of 69 cetaceans species has been obtained from different data sources. Through analysis by a Hierarchical Partitioning test, a non-parametric substitute of variance analysis, the absence of statistical differences between bioacoustic data sources has been demonstrated. Sounds were normalized and the fundamental frequency of each species was determined by autocorrelation. Also, the average swimming speed of each species was obtained from published papers. Finally, the intensity of the Doppler effect was calculated for each species using the mathematical equation of underwater sound physics. Doppler shifts lower than 160Hz were found for the majority of species. This can be explained as a behavioral strategy to avoid depredation by Killer Whales. Only certain species of Ziphidae (genus Mesoplodon, Indopacetus pacificus and Ziphius cavirostris) and six species of Delphinidae (from Lagenorhynchus and Cephalorhynchus genus) present higher Doppler shifts. These species had found other strategies to avoid depredation such as the use of echolocation only in deep waters, very high average swimming speeds, large flocks or the use of very high frequencies. From these results it is possible to conclude that depredation conditions all the evolution of echolocation signals of cetaceans except in a reduced number of species that had developed different behavioral strategies to escape from Killer Whales. [Copyright &y& Elsevier]