Evidence of a Lombard response in migrating humpback whales (Megaptera novaeangliae)

• Published in: The Journal of the Acoustical Society of America
• Main Authors: Dunlop, Rebecca A., Cato, Douglas H., Noad, Michael J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: A I P Publishing LLC 2014
• Subjects: Agroacoustics; Acoustic sensing; Acoustic noise measurement; 1201 Architecture; 3102 Acoustics and Ultrasonics; Lombard; baleen whale; Humpback Whale; Megaptera novaeangliae
• Online Access: https://espace.library.uq.edu.au/view/UQ:335659/UQ335659_OA.pdf; https://espace.library.uq.edu.au/view/UQ:335659

The Lombard reflex is an increase in the subject's vocal levels in response to increased noise levels. This functions to maintain an adequate signal-to-noise ratio at the position of the receiver when noise levels vary. While it has been demonstrated in a small number of mammals and birds including some whales, it has not yet been shown to occur in one of the most vocal species of baleen whale, the humpback whale (Megaptera novaeangliae). Humpback whales were simultaneously visually and acoustically tracked (using an array of calibrated hydrophone buoys) as they migrated southward. Source levels of social vocalizations were estimated from measured received levels and a site-specific empirical sound propagation model developed. In total, 226 social vocalizations from 16 passing groups of whales were selected for final analysis. Noise levels were predominantly wind-dependent (from sea surface motion) and ranged from 81 to 108 dB re 1 mu Pa in the 36Hz-2.8 kHz band. Vocalization source levels increased by 0.9 dB for every 1 dB increase in wind-dependent background noise levels, with source levels (at 1 m) being maintained similar to 60 dB above the noise level. (C) 2014 Acoustical Society of America.