Migrating birds do not carry a single “GPS”. The Cornell Lab of Ornithology and USGS describe a set of cues that complete one another: Sun, stars, magnetic field, shorelines, smell, experience. If one channel fails — overcast sky, for instance — others remain.

By day, many species use the Sun as a compass, corrected by an internal clock, because the star moves across the sky. At night, the apparent rotation of the stars gives direction to nocturnal migrants.

Earth’s magnetic field supplies heading and, in some experiments, information linked to strength or inclination. The exact biological mechanism is still under study: light-dependent reactions in the retina and magnetic particles are among the ideas. A general article does not pick one theory as a closed fact.

Near a destination, rivers, coasts, mountains and vegetation become maps. Some species, including classically studied pigeons, can learn a regional olfactory map and combine it with a compass.

Part of the route is inherited: young of some species leave in the right direction without having flown it. In others, adults pass the path in groups. Experience improves stopovers. Artificial light, weather and lost habitat can divert flocks.

Capacities differ by species and stage. Navigation is a flexible system, not a single compass.

The reference remains the comparative biology of migration, not a metaphor of human wayfinding.

Image: Canada geese in formation, Pittsfield Township, Michigan / Wikimedia Commons. Inland, not a flock over the sea. Cropped to 16:9.

Source consulted: The Basics of Bird Migration: How, Why, and Where | Cornell Lab of Ornithology; Bird Migration | U.S. Geological Survey.