Many animal species exhibit a diel, 24-hr pattern of activity, which is steered by timing cues, with the daily light–dark cycle considered the most powerful. This cue, however, is reduced in polar zones under continuous daylight conditions associated with the midnight sun. The rhythm of animal behaviour under such conditions is poorly understood. Here, we examine periodicity and patterns of daily activity (colony attendance and foraging) in a High-Arctic seabird, the little auk (Alle alle). We demonstrated a regular rhythm of colony attendance at the population level, with birds being the most abundant in the colony during hours of relatively low sun elevation. This pattern is likely to be associated with predation pressure that may be perceived by birds as lower during hours with low sun elevation, because of better predator detectability. Regarding rhythms at an individual level, however, we found the most common periodicity to be 23.2 hr (range from 19.9 hr to 30.8 hr) but no clear pattern of daily colony attendance of individuals. Such a flexibility in daily rhythms indicates that individuals may become arrhythmic in regard to the 24-hr environmental cycle, despite regularities observed at the population level. Finally, we compared males and females in terms of daily activity patterns but we did not find significant sex differences.

中文翻译：

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午夜阳光下的小海雀：北极夏季小型潜水海鸟的日常活动节奏

许多动物物种表现出一种昼夜、24 小时的活动模式，由时间线索控制，其中每天的明暗循环被认为是最强大的。然而，在与午夜太阳相关的连续日光条件下，这种暗示在极地地区会减少。人们对这种条件下动物行为的节奏知之甚少。在这里，我们研究了高北极海鸟小海雀 (Alle alle) 的日常活动（群体出勤和觅食）的周期性和模式。我们在种群水平上展示了群体出勤率的规律性，在太阳高度相对较低的几个小时内，鸟类是群体中最丰富的。这种模式很可能与捕食压力有关，由于捕食者的可探测性更好，鸟类在太阳高度低的几个小时内可能会认为捕食压力较低。然而，关于个体层面的节律，我们发现最常见的周期为 23.2 小时（范围从 19.9 小时到 30.8 小时），但没有明确的个体每日集落出席模式。日常节律的这种灵活性表明，尽管在人口水平上观察到规律性，但个体在 24 小时环境周期方面可能会变得心律不齐。最后，我们在日常活动模式方面比较了男性和女性，但我们没有发现显着的性别差异。尽管在人口层面观察到规律。最后，我们在日常活动模式方面比较了男性和女性，但我们没有发现显着的性别差异。尽管在人口层面观察到规律。最后，我们在日常活动模式方面比较了男性和女性，但我们没有发现显着的性别差异。