The lunar cycle is known to affect the behaviour of strictly nocturnal species, but for diurnal species that are periodically active during the night, this has been less investigated. Nocturnal bird song is relatively common in diurnal species, yet research on this behaviour accounts for little of the research on avian vocalisations. This is surprising given that diurnal species are adapted for bright environments and therefore may be particularly sensitive to change in the lunar cycles. We used automated bioacoustic recorders and automatic song detection software to measure nocturnal song rate in a diurnal bird where both sexes sing, the willie wagtail (Rhipidura leucophrys). We deployed recorders at eight locations across four naturally dark sites resulting in 457 h of nocturnal audio. We confirmed anecdotal evidence suggesting that willie wagtails are prolific nocturnal singers during the breeding season and demonstrate that while both male and females sing during the day, nocturnal song is largely sung by males. Moreover, we show that nocturnal song increased with lunar illumination, contrasting with previous research on other diurnal species that sing at night. Our data allow us to hypothesise possible functions for nocturnal song in this species, such as territory defence or mate attraction. Despite being taxonomically widespread, nocturnal birdsong is largely overlooked in the literature. Anecdotal evidence suggests nocturnal song is positively influenced by the intensity of moonlight but evidence corroborating this is minimal and conflicting. More problematic is that all previous studies are biased towards male song from Northern Hemisphere species. We addressed these gaps by measuring nocturnal song, over the entire lunar cycle, in the willie wagtail, an Australian species. We demonstrate that nocturnal songs are from chorusing males during the breeding season exclusively and that nocturnal song rate increases with lunar illumination. Our work provides a foundation for hypothesizing the function of nocturnal song and contributes to understanding these patterns on a global level.

中文翻译：

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月光变化对昼夜鸟类夜间鸣叫的影响

众所周知，月球周期会影响严格夜间活动的物种的行为，但对于夜间周期性活动的昼夜活动的物种，这方面的研究较少。夜间鸟类鸣叫在昼夜物种中相对常见，但对这种行为的研究在鸟类发声的研究中几乎没有。这是令人惊讶的，因为昼夜物种适应明亮的环境，因此可能对月球周期的变化特别敏感。我们使用自动生物声学记录器和自动歌曲检测软件来测量一种两性都在唱歌的昼夜鸟类，即威利鹡鸪（Rhipidura leucophrys）的夜间歌唱率。我们在四个自然黑暗的地点的八个地点部署了录音机，产生了 457 小时的夜间音频。我们证实了轶事证据，表明威利马尾鹬在繁殖季节是多产的夜间歌唱者，并证明虽然雄性和雌性白天都会唱歌，但夜间歌唱的主要是雄性。此外，我们表明，与之前对夜间唱歌的其他昼夜物种的研究形成鲜明对比的是，夜间歌曲随着月球照明而增加。我们的数据使我们能够假设该物种夜间鸣叫的可能功能，例如领土防御或配偶吸引。尽管在分类学上广泛存在，但夜间鸟鸣在文献中却被很大程度上忽视了。轶事证据表明，夜间歌曲受到月光强度的积极影响，但证实这一点的证据很少且相互矛盾。更成问题的是，之前所有的研究都偏向于来自北半球物种的雄性歌曲。我们通过测量澳大利亚物种威利 wagtail 在整个月球周期的夜间鸣叫来解决这些差距。我们证明，夜间歌曲仅来自繁殖季节期间合唱的雄性，并且夜间歌曲率随着月球照明而增加。我们的工作为假设夜间歌曲的功能奠定了基础，并有助于在全球范围内理解这些模式。我们证明，夜间歌曲仅来自繁殖季节期间合唱的雄性，并且夜间歌曲率随着月球照明而增加。我们的工作为假设夜间歌曲的功能奠定了基础，并有助于在全球范围内理解这些模式。我们证明，夜间歌曲仅来自繁殖季节期间合唱的雄性，并且夜间歌曲率随着月球照明而增加。我们的工作为假设夜间歌曲的功能奠定了基础，并有助于在全球范围内理解这些模式。