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Long-distance bird migration presents a navigational puzzle that has resisted full explanation despite decades of study. Researchers have confirmed that many species can detect the Earth's magnetic field, likely through light-sensitive proteins in the retina, but this sense alone cannot explain how young birds complete their first migration without any adult guide. Some experiments suggest an inherited star map, calibrated by observing the rotation of the night sky during a critical developmental window, works alongside the magnetic sense as a backup or cross-check. Neither mechanism, however, accounts for the precision with which birds return to the exact same breeding site year after year, a feat that likely requires additional memory-based landmarks acquired only after the first journey.