Scientists have known for years that map sense stems from the magnetite in birds' beaks, which measures the strength of the Earth's magnetic field so they recognize home when they get there. But how do they know which direction home is?
Researchers at the University of Oxford have pinpointed a mechanism—in the lab, at least—that may act as a bird's compass. The compound, called a CPF triad, was used for the experiment because it's similar to proteins found in migratory birds' retinas. When illuminated with a blue light typical of dusk, which is when birds orient themselves, CPF formed two unpaired electrons that spin in opposite directions. A magnetic field forced the electrons to align, providing a fixed location for the birds to call north. Avian specialist Henrik Mouritsen of the University of Oldenburg in Germany thinks it's like having a fighter pilot's eyes—like a head-up display, birds can activate a layer of vision to see Earth's magnetic-field lines.