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Magnetoreception - Introduction
»Quelle peut donc être la force physique, partout présente, aussi bien dans les hauteurs de l’atmosphère que dans
la profondeur des flots, qui pourra diriger les légions errantes des animaux migrateurs? Il n’en existe, à mon avis,
qu’une seule, celle qui nous sert aussi à diriger nos navires sur les mers: je veux dire le magnetisme terrestre.«
(Charles Viguier, 1882)
B MAGNETORECEPTION
1 INTRODUCTION
1.1 Magnetoreception in Animals
Magnetoreception is the ability to sense/perceive magnetic cues (intensity and/or the
orientation of the local geomagnetic field) and transfer them to the nervous system, which
extracts, processes, and interprets the relevant information. This information derives from
electrical currents evoked by the Earth’s core and mantle rotating against each other and
creating a magnetic field (cf., Press & Siever 2003). These currents provide relatively constant
and reliable information for orientation because they are always available and uninfluenced by
external factors such as a swiftly shifting cloud cover. In contrast to other compass
mechanisms, such as the star and sun compass, orientation using the magnetic compass is an
innate mechanism (shown for warblers in Wiltschko & Gwinner 1974), corresponding to the
reliability of the Earth’s magnetic field’s information, whose use does not require circadian or
seasonal movements of an external reference. It seems thus clear to view the magnetic
compass as a particularly useful system for the immediate realization of innate nominal
directions and for the calibration of other innate systems.
Animals from a number of groups have been described as possessing and orienting
with a magnetic compass during navigation (cf., Kirschvink et al. 1985, Wiltschko &
Wiltschko 1995). At least in the diverse vertebrate groups, the magnetic compass does not,
however, present a uniform system. While birds (Wiltschko & Wiltschko 1972, 1995) and sea
turtles (Lohmann & Lohmann 1992; Light et al. 1993) magnetically orient via a so-called
inclination compass, fish (Quinn et al. 1981) and subterranean rodents (Marhold et al. 1997a)
use a polarity compass (for further information on the compass types, see B1.5). Amphibians
seem to use both systems in parallel (Phillips 1986).
Despite Aristotle’s observations of regular pre-winterly bird migrations, and despite
the strong evidence from the 19 th century that migratory birds use components of the
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