Mechanisms of Magnetic Orientation in Birds

Behavior and electrophysiological studies have demonstrated a sensitivity to characteristics of the Geomagnetic field that can be used for navigation, both for direction finding (compass) and position finding (map). The avian magnetic compass receptor appears to be a light-dependent, wavelength-sensitive system that functions as a polarity compass (i.e., it distinguishes poleward from equatorward rather than north from south) and is relatively insensitive to changes in magnetic field intensity. The receptor is within the retina and is based on one or more photopigments, perhaps cryptochromes. A second receptor system appears to be based on magnetite and might serve to transduce location information independent of the compass system. This receptor is associated with the ophthalmic branch of the trigeminal nerve and is sensitive to very small (