A Magnetite Null Detector as the Migrating Bird's Compass

The magnetic compass of migrating birds is different from a normal terrestrial compass in that reversing the direction of the magnetic field leaves its reading unchanged. The birds detect the north—south plane as that containing the directions of the earth ’s magnetic field and gravity, and for nort...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 1992-07, Vol.249 (1324), p.27-31
Main Author: Edmonds, Donald T.
Format: Article
Language:English
Subjects:
Birds
Cilia
Compasses
Crystals
Hair cells
Magnetic dipole moment
Magnetic fields
Magnetite
Otolithic membrane
Torque
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Summary:The magnetic compass of migrating birds is different from a normal terrestrial compass in that reversing the direction of the magnetic field leaves its reading unchanged. The birds detect the north—south plane as that containing the directions of the earth ’s magnetic field and gravity, and for north—south discrimination, and also possibly for a map sense of latitude, they detect the angle between the magnetic and gravitational axes within that plane. In this paper it is demonstrated that a biological compass with these characteristics is naturally formed if a biologically synthesized magnetite crystal becomes attached to a torque detector, such as a hair cell. Such a device has the required axial response, despite the polar response of a permanent magnet in a magnetic field, if it acts as a null detector of magnetic torque. It can also integrate at a single site the measurement of the directions of gravity and the magnetic field so that the angle between them is obtained directly.
ISSN:0962-8452
1471-2954
DOI:10.1098/rspb.1992.0079