Underwater Signal Characteristics of Porpoises and Killer Whale as a Function of Size and Acoustic Properties of the Head

Abstract

Analyses of the underwater audio and ultrasonic signals of Orca orcinus (killer whale) in groups and as individuals show both similarities and pronounced differences versus the emissions of smaller porpoises. Acoustic signal content and frequency can be shown to be related to body size, age, and species. Comparative data on the acoustical properties of tissues and bone in the head region are presented, including recently obtained laboratory pulse-tube measurements, following anatomical dissection. Their possible function in formation of the different signal types and in directional listening by these largest animals of the dolphin-porpoise group is discussed relative to the published theories for that of the smaller species. Previous (1965) electroacoustic 13-oct-band (16 Hz-63 kHz) and multispeed oscillographic analyses on the killer-whale signals have shown a number of distinct signal types, including modification of pulse repetition rate, fundamental frequency, and signal complexity during a series of emissions. A more acceptable alternate hypothesis to the layman's assumption of animal conversation is that of a continuous-feedback sonar to permit matching signal and returning echo versus background-noise reverberation and target characteristics. Other signals that may serve communication functions of location and homing, identification, and warning are described in terms of their acoustical parameters.