The mystery of the homing ability of pigeons has been the subject of much i
nterest and it is widely believed that information from the earth's magneti
c field may be involved. However, no specific magnetic sensory organ has ye
t been identified. The recent finding of magnetic materials in the lagenal
otolith of fish and birds raises the possibility that these structures may
be key elements in the elusive magnetic sensory system. For the elemental a
nalysis of materials X-ray fluorescence using synchrotron radiation is one
of the most powerful techniques available and was used in this study for an
alysis of the otoliths. By comparing the compositions of the three differen
t kinds of otoliths among several species of sea fish and birds, we found t
hat the saccular and utricular otoliths rarely contain detectable levels of
iron but that iron is present in significant quantities in the lagenal oto
liths of the birds. The lagenal otolith comprises tiny magnetic particles o
f low inertia that are displaced by imposed magnetic fields, providing the
animal with geomagnetic sensory input, from which the brain would infer nav
igational information.