Effects of a “permanent” clock-shift on the orientation of young homing pigeons

Abstract

1. Young pigeons kept under a 6-h-slow photoperiod from the time of weaning and allowed to see the sun during the afternoon (=their subjective morning) did not depart from test release sites with the 90° deflection ordinarily seen in 6-h-slow clock-shifted pigeons; their orientation did not differ from that of controls. Later exposure of these birds to normal time had the same effect on them as a 6-h-fast clock-shift has on normal pigeons, i.e. it produced a 90° counterclockwise deflection of their bearings. Thus these “permanently” clock-shifted pigeons had learned to read the sun compass in an unusual manner (“morning” sun azimuth=south, etc.). Hence the birds' coupling of time, sun azimuth, and geographic direction is not inherited, but is established by experience. 2. After one or two homing flights in the natural day, the former permanently clock-shifted pigeons oriented correctly, like the controls. When, after one to three months, they were put back under the 6-h-slow conditions of their early development, they did not show the reaction of normal clock-shifted birds. It appeared that they had downgraded the importance of the sun compass and, though probably still using it to some extent, were orienting primarily via other cues. However, when held under normal conditions for a year and then re-shifted 6 h slow, the birds gave deflected bearings. They had apparently recalibrated their sun compass according to the conditions in the natural day, and had resumed using it as a primary cue. 3. Since these results indicate that the calibration of the sun compass by young pigeons is learned, and moreover that the sun compass can later be recalibrated, the question of the underlying reference system for that calibration is raised. Two possibilities are discussed: calibration of the sun compass relative to the magnetic compass, or relative to the coordinates of the navigational “map”. The results thus far do not provide a basis for choosing between these.