Do birds find their way with a map and a compass?

Birds seem to use two tools at once: a compass to know which way to face, and a map to know where they are. Most researchers believe pigeon homing is based on this map-and-compass model: the compass allows the bird to orient, and the map allows it to work out its location relative to home. The pigeon's compass appears to rely on the sun, while the map mechanism has been highly debated.

A sun compass has a problem: the Sun moves, so using it as a compass requires an internal clock. William Keeton tested that by shifting pigeons' body clocks to another time zone in the laboratory. On clear sunny days, those jet-lagged pigeons could not orient correctly, because they could not compensate for the sun's movement. On overcast days, they navigated correctly, which suggests they switch to a magnetic cue when the Sun is hidden. Magnets attached to their backs disrupted that skill.

At night the sky takes over. Warblers in a planetarium oriented south, and when the sky was slowly rotated, they kept their direction relative to the displayed stars. Manx shearwaters released far from home flew back at full speed as long as the Sun or the stars were visible.

Experience matters. A young bird on its first migration flies in the correct direction using Earth's magnetic field, but does not know how far the journey will be. Older ospreys and honey buzzards are better at correcting for wind drift.