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.