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The Initial Orientation of Homing Pigeons at the Magnetic Equator: Compass Mechanisms and the Effect of Applied Magnets
1 Instituto de Ciencias Biomédicas, USP, Sao Paulo, SP, Brasil
2 Beim Kupferhammer 8, 7400 Tübingen, Federal Republic of Germany; Department of Zoology, Duke University, Durham, NC 27706, USA
3 Beim Kupferhammer 8, 7400 Tübingen, Federal Republic of Germany
4 Beim Kupferhammer 8, 7400 Tübingen, Federal Republic of Germany; MPI Verhaltensphysiologie, 8130 Seewiesen, Federal Republic of Germany
To whom reprint requests should be sent.
Homing pigeons are thought to use the earth's magnetic field for direction finding. Though the sensory system and the characteristics of the magnetic field used are unknown, it can be hypothesized that pigeons have an inclination compass, as do some migratory birds. When released at the magnetic equator, this inclination compass ought to be suspended. In addition, releasing pigeons when the sun is at or very close to the zenith renders the sun compass inoperational. However, released under these conditions, homing pigeons are not disorientated. Though they vanish on average in a different direction from pigeons released when the sun compass is available, they still show a directional preference close to magnetic north. This directional preference could be disrupted in some years by the application of magnets to the pigeons' back. In other years this treatment as well as another magnetic treatment did not produce any difference between experimental pigeons and controls. These results confirm once more that, if magnetic effects exist, they are of a rather discrete nature.
Key words: pigeon, homing, magnetism, navigation, magnetic equator, Columba livia
Submitted on June 26, 1991