Birds can get a magnetic map clue

Inclination is the field’s angle to the ground. Declination is the angle between magnetic and geographic north. Researchers tested them as location clues too.

Adult Eurasian reed warblers shifted their mean heading 151° after an 8.5° declination change, as if displaced.

A virtual-displacement test changed inclination and declination, not field strength; birds shifted as if correcting for location. Magnetic cues can map as well as point. 🧭