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First published online December 14, 2005
Journal of Experimental Biology 209, 2-17 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.01960

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Calibration of magnetic and celestial compass cues in migratory birds - a review of cue-conflict experiments

Rachel Muheim^1,2,*, Frank R. Moore³ and John B. Phillips²

¹ Department of Animal Ecology, Lund University, SE-223 62 Lund, Sweden
² Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0406, USA
³ Department of Biological Sciences, University of Mississippi, Hattiesburg, MS 39406-5018, USA

View larger version (33K): [in a new window]   Fig. 1. Deviations from the expected directional shifts of birds that are relying on the magnetic compass in cue conflicts between magnetic and sunset cues during the migratory period (Table 2A, studies not listed in parentheses). The magnetic field shifts are divided into counterclockwise (CCW) and clockwise (CW) shifts and into `against the sun' (AS) and `with the sun' (WS) shifts, since CW and CCW shifts should be interpreted differently by birds living in the northern and southern hemispheres (see text). Filled triangles indicate 90°, open triangles 120° and the rhomboid 115° shifts of the magnetic field. The two half-circles indicate the 0.1% (broken line) and 5% (dotted line) significance level according to the Rayleigh test (Batschelet, 1981). The arrows give the mean direction () and their length is proportional to the mean vector length r with the radius of the circle=1. Outside of the circle the 50% inter-quartile range (IQR) is indicated. Only included are those studies that exposed the birds to sunset cues and where both control and experimental groups exhibited significant unimodal orientation, with a significant shift between treatments, and the control direction did not coincide with the position of the setting sun (Table 2A, studies not listed in parentheses).

View larger version (39K): [in a new window]   Fig. 2. Perception of the magnetic field as a visual pattern of light intensity and/or color (after Ritz et al., 2000). The inclination of the magnetic field in the northern (A) and southern (B) temperate zones will cause this pattern produced by the magnetic field to be `tilted' at a steep angle, with one end of the pattern viewed against the sky and the other viewed against the substrate. Because of positive inclination in the northern and negative in the southern hemisphere, respectively, the upward end of the magnetic axis (where the portion of the pattern is visible against the sky) will be towards geographic South (gS) in the northern hemisphere, and towards gN in the southern hemisphere. Consequently, when the magnetic field is rotated 90° counterclockwise (CCW), the portion of the pattern viewed against the sky will be 90° clockwise (CW) of gN (east) in the northern hemisphere and 90° CCW of gN (west) in the southern hemisphere. Similarly, when the magnetic field is rotated 90° CW, the portion of the pattern viewed against the sky will be 90° CCW of gN (west) in the northern hemisphere and 90° CW of gN (east) in the southern hemisphere. Consequently, lateralization of the light-dependent magnetic compass in the right eye of birds (Wiltschko et al., 2002), or the gradients of light intensity and spectral content associated with the sky at sunrise or sunset, may cause differences in the response to CW and CCW shifts of the magnetic field (see text). In either case, any difference in the birds' response to CW and CCW shifts in experiments carried out in the northern hemisphere, should be reversed in the southern hemisphere (see text).