  How migratory birds can find the right way in navigating over thousand miles
is an intriguing question, which much interested researchers in both fields of
biology and physics for centuries. There several putative proposals that sound
intuitively plausible all remain contested so far because those
hypothesis-models of magnetoreceptor to sense geomagnetic field need either
extremely high sensitivity or humankind-like intelligence to guide. Here we
explore theoretically that the birds can navigate to their destination through
an entirely new scenario to sense the geomagnetic field. Our proposal is based
on separate peaks of the resonance-fluorescence spectrum of a four-level system
derived from the ferric sulfide cluster which exists in a protein complex
(Drosophila CG8198) of migratory birds. As the separation of spectral peaks
contains information about geomagnetic field at both current location and
birthland, the change of such separation cues the bird to choose a right
direction to move and double-resonance emerges once arrived the destination.
Our theoretical mechanism can explain previous experiments on the
disorientation of migratory birds caused by oscillating magnetic field
naturally and more precisely. This work provides insight to explain migratory
navigation and motivates possible manmade practical devices.
