Polarization Sensitivity in Birds

Abstract

Birds can use several environmental cues — sun, stars, geomagnetic field, wind direction, odours, landmarks, sound sources, patterns of the intensity, colour and polarization of skylight — for orientation and navigation (Schmidt-Koenig 1979). Until now, only the homing pigeon (Columba livia) has been shown convincingly to possess a sun compass. The magnetic compass seems increasingly to be central to most avian orientation behaviour. Young migratory birds enter the world with two innate representations of the migration direction, one coded with respect to the geomagnetic field, the other to the celestial rotation ( Wiltschko and Wiltschko 1991). A functional magnetic orientation capability develops in birds that have never seen the sky (e.g. Wiltschko et al. 1998). The preferred migration direction based on magnetic information develops early in life and it may be modified and calibrated by celestial rotation, observed either in clear daytime or at night at least during the first few months of the life of naive migratory birds. This calibration phenomenon was discovered by Bingman (1983) in Savannah sparrows (Passerculus sandwichensis) 1 . Celestial rotation provides information about geographic directions during both day and night. At night, a rotating pattern of artificial stars in laboratory experiments provided a sufficient stimulus to calibrate magnetic orientation in young Savannah sparrows (Able and Able 1990a).