Masking escape in killer whales, stereotypical call design as a noise impact reduction strategy

Abstract

Killer whale call repertoires appear to remain relatively stable over generations because call design is considered socially transmitted between generations. Transmission errors during learning may be responsible for new call designs and repertoire size increases. Call and repertoire divergence may also be the result of adaptation to noisy environments. Temporal and spatial ambient noise variation occurs naturally in killer whale habitats and spans across the auditory frequency ranges of calls. Call components that vary in peak energy across frequency bands appear to escape auditory noise masking because peak amplitude variation per frequency is part of the stereotypical design of calls. As a result level variations in the noise spectrum rather than broadband noise dose may be the more relevant noise impact metrics for calls. Killer whale call design and repertoire divergence appears to reflect the naturally occurring variability in propagation of different frequencies. This may have led to repertoire variation among different populations allowing them to explore different acoustic niches. Presented are preliminary results from an ongoing study into call design influences on signal propagation under varying ambient noise conditions at different times of the year and different geographic locations and water depths within resident and Bigg’s killer whale habitat.