Orientation in birds. The sun compass.

The sun compass was discovered by G. Kramer in caged birds showing migratory restlessness. Subsequent experiments with caged birds employing directional training and clock shifts, carried out by Hoffman and Schmidt-Koenig, showed that the sun azimuth is used, and the sun altitude ignored. In the laboratory, McDonald found the accuracy to be +/- 3 degrees(-)+/- 5 degrees. According to Hoffmann and Schmidt-Koenig, caged birds trained at medium northern latitudes were able to allow for the sun's apparent movement north of the arctic circle, but not in equatorial and trans-equatorial latitudes. In homing experiments, and employing clock shifts, Schmidt-Koenig demonstrated that the sun compass is used by homing pigeons during initial orientation. This finding is the principal evidence for the existence of a map-and-compass navigational system. Pigeons living in equatorial latitudes utilize the sun compass even under the extreme solar conditions of equinox, achieving angular resolution of about 3 degrees in homing experiments. According to preliminary analyses, the homing pigeons' ephemerides are retarded by several weeks (Ranvaud, Schmidt-Koenig, Ganzhorn et al.).