Many terrestrial and marine species have a diel activity pattern, and their acoustic signaling follows their current behavioral state. Whistles and echolocation clicks on long-term recordings produced by melon-headed whales (Peponocephala electra) at Palmyra Atoll indicated that these signals were used selectively during different phases of the day, strengthening the idea of nighttime foraging and daytime resting with afternoon socializing for this species. Spectral features of their echolocation clicks changed from day to night, shifting the median center frequency up. Additionally, click received levels increased with increasing ambient noise during both day and night. Ambient noise over a wide frequency band was on average higher at night. The diel adjustment of click features might be a reaction to acoustic masking caused by these nighttime sounds. Similar adaptations have been documented for numerous taxa in response to noise. Or it could be, unrelated, an increase in biosonar source levels and with it a shift in center frequency to enhance detection distances during foraging at night. Call modifications in intensity, directionality, frequency, and duration according to echolocation task are well established for bats. This finding indicates that melon-headed whales have flexibility in their acoustic behavior, and they collectively and repeatedly adapt their signals from day- to nighttime circumstances.

中文翻译：

---

瓜头鲸的声学行为随昼夜循环而变化

许多陆地和海洋物种具有昼夜活动模式，它们的声学信号遵循它们当前的行为状态。帕尔米拉环礁甜瓜头鲸（Peponocephala Electra）产生的长期录音的哨声和回声定位点击表明，这些信号在一天的不同阶段被有选择地使用，加强了夜间觅食和白天休息的想法，下午为此进行社交物种。他们的回声定位点击的频谱特征从白天到黑夜都在变化，使中值中心频率向上移动。此外，在白天和晚上，随着环境噪音的增加，点击接收水平也会增加。宽频带上的环境噪声在夜间平均更高。点击功能的 diel 调整可能是对由这些夜间声音引起的声学掩蔽的反应。已经记录了许多分类群对噪音的类似适应。或者，它可能与生物声纳源水平的增加无关，并且中心频率发生变化，以增加夜间觅食期间的探测距离。根据回声定位任务在强度、方向性、频率和持续时间方面的呼叫修改对于蝙蝠来说是很好的。这一发现表明，瓜头鲸的声学行为具有灵活性，它们从白天到夜间情况下集体和反复地调整信号。生物声纳源水平的增加以及中心频率的变化，以提高夜间觅食期间的探测距离。根据回声定位任务在强度、方向性、频率和持续时间方面的呼叫修改对于蝙蝠来说是很好的。这一发现表明，瓜头鲸的声学行为具有灵活性，它们从白天到夜间情况下集体和反复地调整信号。生物声纳源水平的增加以及中心频率的变化，以提高夜间觅食期间的探测距离。根据回声定位任务在强度、方向性、频率和持续时间方面的呼叫修改对于蝙蝠来说是很好的。这一发现表明，瓜头鲸的声学行为具有灵活性，它们从白天到夜间情况下集体和反复地调整信号。