EXPERIMENTS ON BIRD ORIENTATION *.

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Summary.: The Starling's ability to reproduce constant compass directions has been demonstrated in two ways: (1) by using the migratory activity as an indicator: the bird tends in a constant direction; (2) by training the bird to choose one of several (up to 12) feeders, symmetrically distributed round the experimental cage. If the incidence of light is changed by use of a mirror arrangement, the direction chosen by the Starling changes correspondingly. More particularly, it has been proved that the sun is the governing factor. The orientation faculty (in experimental conditions) vanishes if the sun is hidden.The correct direction is reproduced regardless of the time of day. Care has been taken to confirm this ability to allow for the daily movement of the sun. The bird is shown to respond correctly even to an artificial sun with fixed azimuth‐position. In this case the direction indicated by the bird is not constant in relation to the compass, but changes progressively, following the sun's path in the reverse sense.The explanatory value of the sun orientation is discussed. At the present stage of our knowledge other orientation mechanisms besides that demonstrated here must be considered. Particularly it is thought that orientation by night in terms of the sun‐orientation is not satisfactory.New experiments itre described which show that homing pigeons are able to home straightaway over an unknown stretch of 200 miles. Some sort of astronomical navigation is suggested by the fact that the pigeons seem to be orientated even before starting. Several other hypotheses are clearly ruled out. Sun‐navigation is being taken as a working hypothesis in further experiments.Apart from this orientation method, direction‐learning can be produced by training the pigeons along one homing line. By displacing the birds sideways they are misled, this being the test of direction‐learning.Pigeons, like Starlings, can be trained to choose food from a definite direction under experimental conditions. Here, too, the sun is the physical clue for orientation. In pigeons, too, the ability to compensate for the daily sun‐movement has been demonstrated.

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