How Animals Return Home?

A large variety of animals has the ability to sense the geomagnetic field and utilize it as a source of directional
(compass) information. There are a lot of stories about how dogs, cats and other animals found a ways to go to return home. It is not known by which biophysical mechanism this magnetoreception is achieved. We investigate
the possibility that magnetoreception involves radical-pair processes that are governed by anisotropic hyperfine coupling
between (unpaired) electron and nuclear spins. We will show theoretically that fields of geomagnetic field strength and weaker
can produce significantly different reaction yields for different alignments of the radical pairs with the magnetic field. As a
model for a magnetic sensory organ we propose a system of radical pairs being 1) orientationally ordered in a molecular
substrate and 2) exhibiting changes in the reaction yields that affect the visual transduction pathway. We evaluate threedimensional
visual modulation patterns that can arise from the influence of the geomagnetic field on radical-pair systems. The
variations of these patterns with orientation and field strength can furnish the magnetic compass ability of birds with the same
characteristics as observed in behavioral experiments. We propose that the recently discovered photoreceptor cryptochrome
is part of the magnetoreception system and suggest further studies to prove or disprove this hypothesis.
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