Figure 3.

Compass calibration by PL cues near the horizon at sunrise and sunset, when the band of maximum polarization and the e-vector vertically intersect the horizon. (a) Three-dimensional and (b) two-dimensional illustrations of the band of maximum polarization at sunrise (left) and sunset (right). Black arrows indicate the alignment of the e-vector intersecting the horizon vertically. (c) Averaging sunrise and sunset calibration provides the birds with a true geographical calibration reference, which is independent of season and latitude. gN, gS, gE, gW , geographical north, south, east and west, respectively.