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Trends in Comparative Biochemistry & Physiology   Volumes    Volume 8 
The sun and the magnetic field in the orientation of equatorial sandhoppers
A. Ugolini
Pages: 137 - 145
Number of pages: 9
Trends in Comparative Biochemistry & Physiology
Volume 8 

Copyright © 2001 Research Trends. All rights reserved


The sun is used as a compass reference by a large array of animal species. However, some aspects of chronometric compensation for the apparent motion of the sun in temperate latitudes are not yet fully understood. At the equator, the use of the sun as a compass is far more difficult, at least from a theoretical point of view. In fact, the sun changes declination twice a year: for 6 months it culminates to the South with a clockwise azimuthal variation, while for the other 6 months it culminates to the North moving in a counterclockwise direction. Its speed on the horizontal plane is far from constant during the year and the day. Finally, twice a year it reaches the zenithal position during which it does not furnish any azimuthal information. The sandhoppers Talorchestia martensii of Somali and Kenya and Talorchestia tricornuta of Gabon were tested to investigate the compass mechanisms they use during their excursions along the Y (sea-land) axis. Releases were performed in a confined environment (a plexiglas bowl) in different seasons (solstitial and equinoctial phases of the sun), in different hours of the day, under the sun or an overcast sky, in a dark room, with or without the natural magnetic field, and with the magnetic field artificially deflected. The results demonstrate the use of both compass references (the sun and the geomagnetic field). The sun compass is used when the azimuthal speed is less than 15°/h (i.e. the sun does not move too much from East or West). When the sun apparently moves rapidly on the horizontal plane and/or when its zenithal distance is less than 10°, the magnetic field is the compass reference used for Y axis orientation.

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