  Migratory birds and other species have the ability to navigate by sensing the
geomagnetic field. Recent experiments indicate that the essential process in
the navigation takes place in bird's eye and uses chemical reaction involving
molecular ions with unpaired electron spins (radical pair). Sensing is achieved
via geomagnetic-dependent dynamics of the spins of the unpaired electrons. Here
we utilize the results of two behavioral experiments conducted on European
Robins to argue that the average life-time of the radical pair is of the order
of a microsecond and therefore agrees with experimental estimations of this
parameter for cryptochrome --- a pigment believed to form the radical pairs. We
also found a reasonable parameter regime where sensitivity of the avian compass
is enhanced by environmental noise, showing that long coherence time is not
required for navigation and may even spoil it.
