Raichel [``Cetacean perception of the environment---A theoretical approach,'' J. Acoust. Soc. Am. 92, 2423(A) (1992)] postulated that cetaceans possess the ability to assess their surroundings through evaluation of acoustic reflections by resolving the presence of higher frequencies that arise from the inherently nonlinear nature of the sound propagation of the pulses that they emit. Palakal et al. [``An acoustic perception model for echolocation signals,'' J. Acoust. Soc. Am. 99, 2558(A) (1996)] developed a neurological model to explain the formation of auditory images as the mechanism of echolocation in bats. Time lapses for the return of echoes constitute the basis for perception of target distance and structural information. The manner in which cetaceans and bats use sound to navigate, find nourishment, and communicate must be quite similar, particularly since higher frequencies provide the key to precision of echolocation and target compliances. Nonreciprocity of signals bounced back to sources supplies additional information on the presence of variations in density, compliances, particle sizes, etc., in the propagation medium. It is also noted that the contortions of the melon of a beluga whale (Delphinapterus leucas) approximates the optimal shape of a radome for emitting and receiving signals.