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The use of radar in migration studies has been invaluable in determining direction of mass movement, dates and times of departure, height of travel, and general volume, especially at night. One interesting fact to come out of current radar work is the discovery of relatively large movements of warblers and other land birds migrating over the seas rather than along the coastlines and in directions observers were completely unaware of a few years ago.

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Orientation and Navigation

Studies on how migrating birds orient (travel in one compass direction) or navigate (travel toward a specific goal) have received increasing emphasis in the past 20 years. These studies have focused on the ability of birds to orient themselves by the position of the sun and stars. Outstanding in this facet of research have been the works of Matthews (1951, 1955), Kramer (1952, 1959, and 1961), Sauer and Sauer (1960), Mewaldt and Rose (1960), Sauer (1961), Hamilton (1962a, b), Schmidt-Koenig (1963, 1964), and Emlen (1969). The basic method used in the experiments is to observe the direction in which confined birds attempt to move during the period of migratory restlessness. The birds are not permitted to have any view of the landscape but only the sky above them. In some cases the positions of the celestial bodies are changed by the use of mirrors to see the effect on the orientation of the experimental birds. In other cases the experiments are performed in planetariums so positions of the stars in the artificial heavens can be manipulated and the effect observed.