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 μPa in the 36 Hz–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 ∼60 dB above the noise level.
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July 2014
July 01 2014
Evidence of a Lombard response in migrating humpback whales (Megaptera novaeangliae)
Rebecca A. Dunlop;
Rebecca A. Dunlop
a)
School of Veterinary Science,
University of Queensland
, Gatton, Queensland 4343, Australia
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Douglas H. Cato;
Douglas H. Cato
b)
Defence Science and Technology Organisation, Australian Technology Park, Eveleigh, New South Wales 1430,
Australia
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Michael J. Noad
Michael J. Noad
School of Veterinary Science,
University of Queensland
, Gatton, Queensland 4343, Australia
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a)
Author to whom correspondence should be addressed. Electronic mail: r.dunlop@uq.edu.au
b)
Also at: University of Sydney Institute of Marine Science, Sydney, NSW 2006, Australia.
J. Acoust. Soc. Am. 136, 430–437 (2014)
Article history
Received:
November 28 2013
Accepted:
May 21 2014
Citation
Rebecca A. Dunlop, Douglas H. Cato, Michael J. Noad; Evidence of a Lombard response in migrating humpback whales (Megaptera novaeangliae). J. Acoust. Soc. Am. 1 July 2014; 136 (1): 430–437. https://doi.org/10.1121/1.4883598
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