The lunar cycle drives migration of a nocturnal bird

Every year billions of seasonal migrants connect continents by transporting nutrients, energy and pathogens between distant communities and ecosystems. For animals that power their movements by endogenous energy stores, the daily energy intake rates strongly influence the speed of migration. If access to food resources varies cyclically over the season, migrants sensitive to changes in daily energy intake rates may adjust timing of migration accordingly. As an effect, individuals adjusting to a common temporal cycle are expected to approach synchrony in foraging and movement. A large-scale periodic pattern, such as the dark-light cycle of the moon, could thus synchronize migrations across animal populations. However, such cyclic effects on the temporal regulation of migration has not been considered. Here we show the temporal influence of the lunar cycle on the movement activity and migration tactics in a visual hunting nocturnal insectivore and long-distance migrant, the European nightjar Caprimulgus europeaus. We found that the daily foraging activity more than doubled during moon-lit nights, likely driven by an increase in light-dependent fuelling opportunities. This resulted in a clear cyclicity also in the intensity of migratory movements with occasionally up to 100 % of the birds migrating simultaneously following periods of full moon. We conclude that cyclic influences on migrants can act as an important regulator of the progression of individuals, and synchronise pulses of migratory populations, with possible downstream effects on associated communities and ecosystems.

每年，数十亿只季节性迁徙动物在相距遥远的群落与生态系统之间转运营养物质、能量与病原体，以此实现各大洲之间的连接。对于依靠内源性能量储备为移动提供动力的动物而言，每日能量摄入率会显著影响迁徙速度。若食物资源的可获得性随季节周期性变化，那么对每日能量摄入率变化敏感的迁徙动物，便可据此调整迁徙时机。由此，适应统一时间周期的个体，其觅食与移动行为有望趋于同步。诸如月球明暗周期这类大规模周期性模式，便可实现不同动物种群间迁徙行为的同步。然而，此前尚未有研究考虑此类周期性因素对迁徙时间调控的影响。本研究针对视觉捕猎型夜行食虫动物、长距离迁徙物种——欧夜鹰（Caprimulgus europeaus），揭示了月相周期对其活动行为与迁徙策略的时间维度影响。研究发现，在有月光的夜晚，每日觅食活动量翻倍有余，这一现象可能源于依赖光照的补给机会增多。这也使得迁徙活动强度呈现出显著的周期性：在满月时段过后，偶尔会有高达100%的个体同步启动迁徙。综上，本研究表明，周期性因素对迁徙动物的影响可作为个体迁徙进程的重要调控因子，同步迁徙种群的迁徙脉冲，并可能对相关群落与生态系统产生下游连锁效应。