Avian Geomagnetic Vision?

I am very interested in vision and hacking "The Mind's Eye" in reference to visual perception beyond the sense organs. It has been suggested that some birds migrate using the magnetic force lines of the Earth:
"Currently, theoretical, behavioral and physiological evidences support two magnetic sensing hypotheses: a magnetite-mediated magnetic sense [4]–[6] and/or a vision-mediated magnetic compass [7]." This quote comes from a recently published study of the latter possibility. The full article is really brainy.

[inspired by Street Tech ]