[MARMAM] New publication on male northern elephant seal vocalization source levels and ambient noise in breeding rookeries
brandon.southall at sea-inc.net
Mon Jan 27 09:46:22 PST 2020
My co-authors and I would like to bring to your attention a recent publication on vocalization characteristics and ambient noise in northern elephant seal breeding rookeries. The reference and abstract are given below and the paper is available on request or at: https://asa.scitation.org/doi/10.1121/1.5139422
Southall, B.L., Casey, C., Holt, M., Insley, S., and Reichmuth, C. (2019). High-amplitude vocalizations of male northern elephant seals and associated ambient noise on a breeding rookery. Journal of the Acoustical Society of America. 146, 4514-4524. https://doi.org/10.1121/1.5139422
Northern elephant seals (Mirounga angustirostris ) are massive, land-breeding marine mammals that produce loud, stereotyped calls during annual breeding seasons. To determine vocalization source levels emitted by competing males on a mainland breeding rookery, aerial calls were measured on axis at 1m from adult males using three different sound pressure level metrics. Time-averaged (1 min) ambient noise was also measured under variable environmental and social conditions. Results indicate that male northern elephant seals emit high amplitude airborne calls with little variation in call amplitude. Mean source levels ranged from 98 to 114 dB re: 20 l Pa [root-mean-square (rms) -fast], 102–116 dB re: 20 l Pa (rms-impulse), and 120–131 dB re: 20 l Pa (peak) and average standard deviations for all metrics were < 2.3 dB. Further, these seal rookeries exhibit high variability in ambient noise (in terms of both spectrum and amplitude) from biotic and environmental sources. Finally, males sampled did not adjust call amplitude to compensate for higher background noise levels and thus did not exhibit a Lombard effect. These findings reinforce the view that the remarkable vocalizations of male northern elephant seals serve as rigid and powerful signals that convey individual identity within noisy breeding colonies rather than as honest indicators of size, status, or motivation.
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