The role of the geomagnetic field in the development of birds' compass sense

Abstract

The compass sense of birds is based on both celestial (Sun, sunset, skylight polarization pattern, stars) and geomagnetic cues1–3. Songbirds, from birth prevented from seeing celestial cues, orient by a magnetic compass4,5, and so do young homing pigeons before the development of their Sun compass6,7. Furthermore, young homing pigeons exposed to aberrant solar conditions, acquire a correspondingly erroneous8 or incomplete9 Sun compass. These findings suggest that the magnetic sense may provide a primary and innate reference frame for the calibration/learning of the birds' celestial compass system8,9. We have investigated the role of the geomagnetic field in the development of birds' compass sense, by shifting the geomagnetic field at pied flycatchers' (Ficedula hypoleuca) nests during the incubation and nestling periods. The magnetic field was shifted by Helmholtz coils mounted at the nest-boxes. A corresponding shift in the migratory orientation was observed 2 months later in the young birds' lives. This supports the magnetic calibration hypothesis, indicating imprinting-like learning at an early age of celestial compass cues used in migratory orientation.