  Several experiments over the years have shown that the Earth's magnetic field
is essential for orientation in birds migration. The most promising explanation
for this orientation is the photo-stimulated radical pair (RP) mechanism. In
order to define a reference frame for the orientation task radicals must have
an intrinsic anisotropy. We show that this kind of anisotropy, and consequently
the entanglement in the model, are not necessary for the proper functioning of
the compass. Classically correlated initial conditions for the RP, subjected to
a fast decoherence process, are able to provide the anisotropy required. Even a
dephasing environment can provide the necessary frame for the compass to work,
and also implies fast decay of any quantum correlation in the system without
damaging the orientation ability. This fact significantly expands the range of
applicability of the RP mechanism providing more elements for experimental
search.
