Long Marine Laboratory, Institute of Marine Sciences, University of California Santa Cruz, 115 McAllister Way, Santa Cruz, California 95060, USA.
Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California 95060, USA.
J Acoust Soc Am. 2019 Dec;146(6):4514. doi: 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 1 m 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 μPa [root-mean-square (rms) -fast], 102-116 dB re: 20 μPa (rms-impulse), and 120-131 dB re: 20 μPa (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.
北方象海豹（Mirounga angustirostris）是一种体型巨大的陆生繁殖海洋哺乳动物，在每年的繁殖季节会发出响亮而刻板的叫声。为了确定在大陆繁殖地竞争雄性发出的叫声源水平，使用三种不同的声压级度量标准，在成年雄性 1 米处对轴线上的空中叫声进行了测量。在不同的环境和社会条件下，还测量了时间平均（1 分钟）环境噪声。结果表明，雄性北方象海豹发出高振幅的气载叫声，叫声幅度变化不大。平均源水平范围从 98 到 114 分贝 re：20 μPa [均方根（rms）-快]，102-116 分贝 re：20 μPa（rms 脉冲）和 120-131 分贝 re：20 μPa（峰值），所有度量标准的平均标准偏差均<2.3 分贝。此外，这些海豹繁殖地表现出生物和环境来源的环境噪声（在频谱和幅度方面）高度可变性。最后，采样的雄性没有调整叫声幅度以补偿更高的背景噪声水平，因此没有表现出 Lombard 效应。这些发现强化了这样一种观点，即雄性北方象海豹的非凡叫声是一种刻板而有力的信号，它在嘈杂的繁殖群体中传递个体身份，而不是体型、地位或动机的诚实指标。
