Unlike our senses involving vision, hearing, smell and touch, we do not know what receptors underlie magnetoreception, Ritz said. Migratory birds have long been known to possess a magnetic compass that helps them find the correct direction during their migratory flights. It has remained unknown, however, how birds can detect the direction of the Earths magnetic field.
Now, our study points to what we need to look fora molecular substrate for certain chemical reactions. That is, we can rule out magnetic materials in birds beaks and elsewhere as being possible candidates. Magnetite in the beaks, however, may play a role in detecting the strength but not the direction of the Earths magnetic field.
The experiments on the birds were conducted in a six-week period in 2003 in Frankfurt, Germany, in the laboratory of Wolfgang and Roswitha Wiltschko, co-authors of the paper, who developed the behavioral experimental setup used in the study for testing magnetic orientation in birds. During migratory unrest, the birds could move in their cages. Each cage was funnel-shaped, lined with coated paper and measured approximately 1.5 feet in diameter. When the birds moved in the cages, they left scratch marks that were counted subsequently by the researchers and analyzed.
To produce artificial oscillating fields, the researchers fed high-frequency currents from a signal generator into a coil that surrounded four test cages. The coil, with a diameter of approximately two meters, could be moved to change the alignment of the oscillating field. Each bird was tested once a day during dusk for a period of approximately 75 minutes.