The surrounding magnetic field affects the kind of this correlation (parallel or anti-parallel), and this in turn affects the length of time cryptochrome stays in its activated state.
Activation of cryptochrome may affect the light-sensitivity of retinal neurons, with the overall result that the bird can see the magnetic field.
Yet, it has also been suggested that homing pigeons and other birds use the visually mediated cryptochrome receptor as a compass.
The antennae contain cryptochrome, a photoreceptor protein sensitive to the violet-blue part of the light spectrum.
