Evidence for calibration of magnetic migratory orientation in Savannah sparrows reared in the field

The orientation system of migratory birds consists of a magnetic compass and compasses based upon celestial cues. In many places, magnetic compass directions and true or geographic compass directions differ (referred to as magnetic declination). It has been demonstrated experimentally in several species that the innate preferred direction of magnetic orientation can be calibrated by celestial rotation, an indicator of geographic directions. This calibration process brings the two types of compass into conformity and provides the birds with a mechanism that compensates for the spatial variation in magnetic declination. Calibration of magnetic orientation has heretofore been demonstrated only with hand-raised birds exposed to very large declination (90° or more). Here we show that the magnetic orientation of wild birds from near Albany, New York, USA (declination = 14° W) was N-S, a clockwise shift of 26°from the NNW-SSE direction of birds raised entirely indoors. Hand-raised birds having visual experience with either the daytime sky or both day and night sky orientated N-S, similar to wild-caught birds. These data provide the first confirmation that calibration of magnetic orientation occurs under natural conditions and in response to modest declination values.