A nocturnal mammal, the greater mouse-eared bat, calibrates a magnetic compass by the sun

Abstract

Recent evidence suggests that bats can detect the geomagnetic field, but the way in which this is used by them for navigation to a home roost remains unresolved. The geomagnetic field may be used by animals both to indicate direction and to locate position. In birds, directional information appears to be derived from an interaction of the magnetic field with either the sun or the stars, with some evidence suggesting that sunset/sunrise provides the primary directional reference by which a magnetic compass is calibrated daily. We demonstrate that homing greater mouseeared bats (Myotis myotis) calibrate a magnetic compass with sunset cues by testing their homing response after exposure to an altered magnetic field at and after sunset. Magnetic manipulation at sunset resulted in a counterclockwise shift in orientation compared with controls, consistent with sunset calibration of the magnetic field, whereas magnetic manipulation after sunset resulted in no change in orientation. Unlike in birds, however, the pattern of polarization was not necessary for the calibration. For animals that occupy ecological niches where the sunset is rarely observed, this is a surprising finding. Yet it may indicate the primacy of the sun as an absolute geographical reference not only for birds but also within other vertebrate taxa.navigation | orientation | sun compass | Chiroptera | sensory ecology S ince the discovery that migrating birds can use the geomagnetic field to designate direction, research on the manner in which different animals use this cue for orientation and navigation has flourished (1-4). As a general notion, animals could potentially use the geomagnetic field for obtaining directional information, the "compass sense" (5), and/or to locate position, the "map sense" (6). In birds, a number of seemingly contradictory findings suggested that the geomagnetic field interacts with either the sun or the stars to provide directional information (7). Calibration by such celestial cues may be important in migrating animals to correct for declination error [the difference between geographical and magnetic north (8)] or to avoid increased paths through inaccuracies (9). Recent evidence suggests that polarized light cues at sunset and sunrise may provide the primary directional reference that calibrates a magnetic compass in migrating birds (8)(9)(10)(11).Surprisingly, only recently has it been shown that bats are able to detect the geomagnetic field (12-14), although so far evidence exists only for two species, one in the United States (12, 13) and one in Asia (14). Using the technique of Cochran et al. (8), in which the animal is exposed to an altered magnetic field at sunset and then released into the natural magnetic field, the results of ref. 12 suggested that, like birds, bats used the geomagnetic field to determine direction following calibration by sunset cues. However, this interpretation remains uncertain on two counts. First, the experimental design in ref. 12 involved transport in a variable magnetic field, making it...

Orientation behaviour of leatherback sea turtles within the North Atlantic subtropical gyre

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Magnetic compass orientation in two strictly subterranean rodents: learned or species-specific innate directional preference?

“…Despite the remarkable progress that has been accomplished during the past decade, evidence for magnetoreception in mammals remains fairly limited. Magnetic compass orientation has been convincingly demonstrated in only two species of distantly related subterranean rodents (Burda et al, 1990;Kimchi and Terkel, 2001), two epigeic rodent species (Deutschlander et al, 2003;Muheim et al, 2006) and three bat species (Holland et al, 2006;Holland et al, 2010;Wang et al, 2007). More recently, magnetic alignment has been demonstrated in larger mammals, namely cattle and deer (Begall et al, 2008;Begall et al, 2011;Burda et al, 2009), and in hunting foxes .…”

Polarized skylight does not calibrate the compass system of a migratory bat

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