Input E · SCIENCE ARTICLE — HOW MIGRATORY BIRDS NAVIGATE

MORE THAN ONE COMPASS

Migrating birds combine several kinds of information rather than relying on a single perfect guide.

A

Long-distance migration looks mysterious because birds can cross unfamiliar landscapes, seas and cloudy skies without following roads. Scientists now know that many species combine several navigation cues rather than depending on one perfect system.

B

On clear days, some birds use the position of the sun and adjust for its movement with an internal sense of time. At night, others can use patterns of stars. Young birds may be born with a basic directional programme, but experience helps them improve it.

C

Clouds can hide both the sun and stars, so researchers have also studied magnetic orientation. Experiments suggest that some birds can detect the direction of Earth’s magnetic field. This ability gives them another source of information when visual cues are weak. It does not provide a complete map, however. Wind direction and smell may help certain species, especially near coasts or familiar breeding areas.

D

No single cue works in every situation. Birds may compare several signals, notice when one becomes unreliable and switch attention to another. The exact balance differs between species and even between stages of a journey. Navigation is therefore best understood as a flexible system in which inherited tendencies, learned landmarks and environmental signals support one another.

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