  The radical-pair mechanism is understood to underlie the magnetic navigation
capability of birds and possibly other species. Experiments with birds have
provided indirect and in cases conflicting evidence on the actual existence of
this mechanism. We here propose a new experiment that can unambiguously
identify the presence of the radical-pair magnetoreceptor in birds and unravel
some of its basic properties. The proposed experiment is based on modulated
light excitation with a pulsed laser, combined with delayed radio-frequency
magnetic field pulses. We predict a resonance effect in the birds' magnetic
orientation versus the rf-pulse delay time. The resonance's position reflects
the singlet-triplet mixing time of the magnetoreceptor.
