Fig. 6. Orientation of albatrosses returning from the Peruvian upwelling zone with magnets or shams still attached to their head. Each filled circle indicates the orientation of one section of the return journey, between two satellite fixes at least 100 km apart, for magnet and sham birds, respectively. The broken line indicates the correct homeward direction to Galápagos, and the broken circle indicates the length of the mean vector (solid arrow) required for significance at the 0.001 level according to the Rayleigh test.