Polarized Light Cues Underlie Compass Calibration in Migratory Songbirds
Rachel Muheim,1,2*
John B. Phillips,2
Susanne Åkesson1
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.
1 Department of Animal Ecology, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
2 Department of Biological Sciences, Virginia Polytechnic Institute and State University, Derring Hall, Blacksburg, VA 24061, USA.
* To whom correspondence should be addressed. E-mail: rmuheim{at}vt.edu
