This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. T. Neil Davis is a seismologist at the institute. Careful tests with homing pigeons and other birds displaying the ability to judge direction show that the birds are affected by changing magnetic fields. Small coils placed near the birds' heads to create unnatural magnetic fields there do disturb the ability of pigeons to find home.
Magnetic storms do the same.
If birds are released at places where the earth's magnetic field is anomalously strong, their homing ability is entirely disrupted. A possible reason why birds can sense the earth's magnetic field and perhaps use it for navigation is given by Charles Walcott and co-authors in the 7 September 1979 issue of Science magazine. Dissecting a number of pigeons, these scientists found the equivalent of a compass needle in each pigeon's head. Searches inside this tissue with an electron microscope revealed the presence of more than ten million tiny crystals each four times as long as wide. Other tests demonstrated that these crystals were magnetite, the iron-oxygen compound of which compass needles are made.