Comparative observations on odontocete sonar signals from captive animals

Abstract

In this paper a comparative analysis of typical sonar signals of several species of littoral and riverine dolphins in captivity is presented. The sonar wave shapes compared include those recently obtained from two species, whose acoustic behavior has not been described previously in literature, i.e., the off‐shore Lagenorhynchus albirostris and the fresh water population of Irrawadi; Orcaella brevirostris. The latter fit very well in the picture established thus far from a large collection of echolocation data. A study of these sonar signals reveals the noteworthy fact that—apart from the Commerson's signal—they all share a rather simple, basic wave shape. This can best be understood and classified in terms of the well‐known uncertainty relation in communication theory and enables us therefore to link bioacoustics with mathematical physics. The signals approach the theoretical lower bound for the product of the time duration and frequency bandwidth and could therefore be designated as “small time‐duration bandwidth” signals. They are thus well suited as a class of elementary optimal time‐frequency signals. The frequency range of interest in the first described class of cetacean sonar is situated at a dominant frequency below 100 kHz, while in the Phocaena and Commerson group this dominant value goes up to around 120 kHz. The latter thus enabling those small animals to resolve spatial differences in their habitat up to an order of magnitude of nearly a centimeter.