Magnetic declination stops migratory birds getting lost at sea

In the 1700s, scientists, sailors, engineers and explorers were trying to work out how to navigate east to west at sea. The stakes were high; many lives were lost because sailors could not reliably measure longitude. Eventually, the invention of accurate timepieces allowed sailors to use the time in their current location, and the time at a fixed reference, to calculate longitude. But how do long-distance migrants navigate longitude at sea without a time-difference clock sense? Nikita Chernetsov of the Zoological Institute of Russian Academy of Sciences and an international team of collaborators suspected that for Eurasian reed warblers, magnetic fields might provide an answer.