Advanced spatial-learning adaptations have been shown for migratory songbirds (1], but it is not well known how the simple genetic program encoding migratory distance and direction in young birds [2-4] translates to a navigation mechanism used by adults [2, 4-6]. A number of convenient cues are available to define latitude on the basis of geomagnetic and celestial information [7-15], but very few are useful to defining longitude [12-15]. To investigate the effects of displacements across longitudes on orientation, we recorded orientation of adult and juvenile migratory white-crowned sparrows, Zonotrichia leucophrys gambelii, after passive longitudinal displacements, by ship, of 266-2862 km across high-arctic North America. After eastward displacement to the magnetic North Pole and then across the 0 degrees declination line, adults and juveniles abruptly shifted their orientation from the migratory direction to a direction that would lead back to the breeding area or to the normal migratory route, suggesting that the birds began compensating for the displacement by using geomagnetic cues alone or together with solar cues. In contrast to predictions by a simple genetic migration program, our experiments suggest that both adults and juveniles possess a navigation system based on a combination of celestial and geomagnetic information, possibly declination, to correct for eastward longitudinal displacements.