Migratory birds are known to use the geomagnetic field as a source of compass information. There are two competing hypotheses for the primary process underlying the avian magnetic compass, one involving magnetite, the other a magnetically sensitive chemical reaction. Here we show that oscillating magnetic fields disrupt the magnetic orientation behaviour of migratory birds. Robins were disoriented when exposed to a vertically aligned broadband (0.1-10 MHz) or a single-frequency (7-MHz) field in addition to the geomagnetic field. Moreover, in the 7-MHz oscillating field, this effect depended on the angle between the oscillating and the geomagnetic fields. The birds exhibited seasonally appropriate migratory orientation when the oscillating field was parallel to the geomagnetic field, but were disoriented when it was presented at a 24 degrees or 48 degrees angle. These results are consistent with a resonance effect on singlet-triplet transitions and suggest a magnetic compass based on a radical-pair mechanism.

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Migratory songbirds use the geomagnetic field, stars, the Sun, and polarized light patterns to determine their migratory direction. To prevent navigational errors, it is necessary to calibrate all of these compass systems to a common reference. We show that migratory Savannah sparrows use polarized light cues from the region of sky near the horizon to recalibrate the magnetic compass at both sunrise and sunset. We suggest that skylight polarization patterns are used to derive an absolute (i.e., geographic) directional system that provides the primary calibration reference for all of the compasses of migratory songbirds.

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Laboratory tests were carried out to examine the orientation behavior of adult Eastern red-spotted newts (Notophthalmus viridescens) to earth-strength magnetic fields. Groups of 30 to 40 newts were housed in water-filled, all-glass aquaria with an artificial shoreline at one end. The aquaria were located in a greenhouse or outdoors adjacent to the laboratory building, and aligned on either the magnetic north-south or east-west axis. Tests were carried out in an enclosed indoor arena. Newts were tested in four horizontal alignments of the magnetic field: the ambient magnetic field (magnetic north at North) and three altered fields (magnetic north rotated to East, South or West). Data were analyzed after pooling the magnetic bearings from all four conditions in such a way as to retain the component of the newts' orientation that was a consistent response to the magnetic field. Elevation of training tank water temperature was used to increase the newts' motivation to orient in the direction of shore. Newts exposed to a training tank water temperature of 33-34 degrees C just prior to testing exhibited consistent unimodal magnetic compass orientation. The direction of orientation was altered predictably by changing training tank alignment and location relative to the laboratory building. The results provide the first evidence of a strong, replicable magnetic compass response in a terrestrial vertebrate under controlled laboratory conditions. Further, the present study demonstrates that the Eastern newt is able to learn a directional response relative to the earth's magnetic field.

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues.

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. Calibration of magnetic and celestial compass cues in migratory birds -a review of cue-conflict experiments. J. Exp. Biol. 209, 2-17.The final paragraph before the 'General discussion' (p. 11) was based on a misunderstanding and should be replaced by the following paragraph:It was previously argued that during migration only one exposure to the cue conflict would lead to a dominance of celestial cues, and thus to a recalibration of the magnetic compass, while repeated exposures to the cue conflict would lead to a dominance of magnetic cues and to a recalibration of the celestial compass(es) (e.g. Wiltschko et al., 1997;Wiltschko et al., 1998a;. According to our analysis, the birds did not show a significant reaction to the shifted magnetic field, i.e. they followed celestial rather than magnetic cues in four of 23 experiments in which birds were exposed to a shifted magnetic field with access to celestial cues at sunrise/sunset during migration (Table·2A). These were experiments in which the birds were tested only once and, consequently, had only one exposure to the cue conflict (Table·2Aa,b,o,p). However, all four experiments were also carried out in funnels that restricted the view of the birds to 90°around the zenith. In the remaining nine experiments in which the birds were tested only once, they did show a significant shift when the magnetic field was rotated, and in all of these experiments the birds had a view of the sky that was 160°around the zenith. Consequently, a restricted view of the sky, rather than a single exposure to the cue conflict, appears to account for the absence of a response to the shifted magnetic field in the four experiments (Table·2Aa,b,o,p).The conclusions of the manuscript are unaffected, and the authors apologise for these errors and any inconvenience caused. IntroductionMigrating birds have an inherited migratory program coding the general direction and distance to be travelled (reviewed by Berthold, 1991Berthold, , 1996Gwinner, 1996), and they use several different compass systems to determine the seasonally appropriate migratory direction. They use compass information derived from the geomagnetic field (reviewed by Wiltschko and Wiltschko, 1995), star patterns (Sauer, 1957;Migratory birds use multiple sources of compass information for orientation, including the geomagnetic field, the sun, skylight polarization patterns and star patterns. In this paper we review the results of cue-conflict experiments designed to determine the relative importance of the different compass mechanisms, and how directional information from these compass mechanisms is integrated. We focus on cue-conflict experiments in which the magnetic field was shifted in alignment relative to natural celestial cues. Consistent with the conclusions of earlier authors, our analyses suggest that during the premigratory season, celestial information is given the greatest salience and used to recalibrate the magnetic compass by both juvenile and adult birds. Sunset polarized light patterns from the region of the s...