Experimental Manipulation of the Orientational Clock in Birds

Numerous experiments with birds displaced during their migration, and a great number of homing experiments with several wild bird species, as well as with homing pigeons, show that birds must possess at least two different orientational mechanisms [1, 2, 3, 4, 5]. Juvenile birds displaced transversely to their normal route, before or during their first trip to wintering quarters, fly on in the original direction after displacement, as recoveries of marked birds show. They take a course parallel to the normal migratory route. What they use for orientation must be a sort of compass to find their direction. Adult birds, however, may head straight to their breeding places or wintering areas if displaced, though they have to fly in directions that differ from their normal migratory course, and have to pass over long stretches of area unknown to them. For this performance they must be gifted with the ability to...