Geomagnetic Position Fixing

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Summary The proposed research will investigate the ability of a vertebrate to use gradients in the inclination or 'dip angle' of the earth's magnetic field (defined as the angle between the magnetic field lines and gravity) to determine geographic ("map") position. Previous studies of homing orientation have shown that magnetic inclination may be used to derive one coordinate of a navigational map. To provide a more rigorous test of magnetic inclination's role in providing map information, the effects of small changes in magnetic inclination on homing orientation will be used to estimate characteristics of the local gradient of magnetic inclination within an animal's home range, e.g., the "home value" of inclination and the alignment of the gradient. These behaviorally derived estimates will then be compared with actual measured values obtained by mapping the spatial gradients of magnetic inclination around the sites where animals were collected. A comparison of the response of animals collected at sites along the north-south and east-west axes relative to our testing site will also be used to help distinguish "map" and "non-map" effects resulting from changes in magnetic inclination, and to determine whether a true bicoordinate map is being used to determine geographic position. The proposed experiments will contribute to a better understanding of the magnetic field's role in the map component of homing. These experiments will also help to determine the lower limits of the sensitivity of biological systems to variation in the geomagnetic field and, at a more general level, to determine the precision with which the vertebrate nervous system can measure the absolute values of physical stimuli.