UBC Theses and Dissertations
Bio-acoustics of the gray whale (Eschrichtius robustus) Dahlheim, Marilyn Elayne
Gray whales (Eschrichtius robustus), while engaged in underwater signalling, circumvent noise in the acoustical channel by the structure and timing of their calls. Data yielding this conclusion were collected during an acoustical study on gray whales and their habitats (1981-1984). Sonographic analyses of tape recordings were used to quantify the acoustical repertoire, the ambient noise characteristics of the area, and the relationship between the animals' calls and the environment. The acoustical responses of whales to artificially increased levels of noise were documented during playback experimentation in Mexico. Nine sound parameters were inspected and compared between control and experimental conditions: calling rates, call types, frequency range of signals (Hz), emphasized frequencies (Hz), received levels of sounds (dB re 1 μPa), call duration (sec), percentage of calls exhibiting frequency modulation, number of pulses per series, and repetition rates of signals. The observed surface behavior of gray whales in response to noise (i.e., dive durations, movements and abundance) was also investigated. Analyses yielded: a description of gray whale call types; a characterization of the acoustical habitats occupied by this species, including a list of sources contributing to the ambient noise and a profile of the propagation characteristics of the study area; a determination of the relationship between whale calls and their habitats; and the acoustical capabilities and strategies of whales in response to noise. The plasticity observed in the overall behavior of this whale is of adaptive significance when considering the dynamic nature of noise in the environment. Typically, the multiple strategies employed by the whales when faced with various noise situations enable them to minimize the detrimental effect that noise has on their underwater signalling. Gray whale responses varied with the sound source and may also differ relative to the geographical range and/or general behavior of the animal. It is concluded that ambient noise (both natural and man-made) has a profound effect on the behavior of this coastal species and that acoustical calling is modified to optimize signal transmission and reception.
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