Dusk seems to trigger birds’ nighttime migrations

Birds that migrate at night seem to take their cues from the arrival of dusk, researchers found. Biologists suspect the nighttime flights help them to avoid predators and the heat of the day, allowing them to spend daylight hours foraging. But they’ve wondered about what triggers the birds to fly when they do. In a recent study in Movement Ecology, researchers put radio tracking devices on nearly 400 migratory songbirds from to nine species.

Ninety percent that seemed poised to set off on their seasonal migrations did so within 69 minutes of dusk. “This is a really tight window, which suggests there is something important about this time of night,” said Nathan Cooper, a research ecologist for the Smithsonian’s National Zoo and Conservation Biology Institute and the papers’ first author, in a news release.

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