Reed warblers have a sense for magnetic declination

Researchers recently showed that migratory reed warblers depend on an internal geomagnetic map to guide them on their long-distance journeys. But it wasn’t clear how the birds were solving the difficult ‘longitude problem,’ determining where they were along the east-west axis and which way to go. The team’s latest report shows birds rely on changes from east to west in magnetic declination, the angular difference between geographic north and magnetic north.