Lunar cycle and moonlight intensity influence nocturnal migration patterns in a small songbird.

Lunar cycle and moonlight exposure have significant impacts on animal behaviour and physiology. The presence or absence of moonlight, along with predictable changes in brightness throughout the lunar cycle, can shape reproduction, foraging, communication, and other aspects of an animal's world. While it has been shown that invertebrates use the moonlight for orientation, little is known on the effect of the lunar cycle on migratory birds. We found that the lunar cycle affected the nocturnal migration activity of a diurnal songbird species, the Eurasian Skylark Alauda arvensis. The occurrence of birds increased with moon fraction, moonlight intensity and duration, while abundance correlated positively with increasing moonlight intensity. Our findings of increased migration activity in bright nights around full moon contradict previous assumptions that small bird migrants would avoid such nights due to increased predation pressure and decreased visibility of stars for orientation. We argue that migrants relying on visual cues for orientation might favour moonlit nights, while future studies should also test whether the position of the moon can be used for navigation by birds.