'Nonsense' orientation in Mallard; a resum and an investigation of the mechanism of a sun-compass
The state of knowledge on fixed direction 'nonsense' orientations is reviewed, with particular emphasis on those shown by the Mallard Anas platyrhynchos. A detailed report is given of 12-hour time-shifting tests whereby Mallard were released by day in their physiological night, to determine how the angle-correcting mechanism of a sun-compass operates between sunset and sunrise. The results support the hypothesis that the angle-correction, having been closed up during the day to take account of the sun's apparent movement across the southern sky, is opened out again throughout the night, as if the sun ran back through the south rather than on through the north. A parallel with Ancient Egyptian mythology is mentioned. Tests on the scale reviewed are unlikely to be possible hereafter because of the decline in catching ability of duck decoys. Ironically this is due to the success of conservation measures.
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