Orientation Strategies Used by Free-Flying Bird Migrants:
A Radar Tracking Study

Emlen, S.T. & Demong, N.J. (1978). In: Animal Migration, Navigation and Homing. K. Schmidt-Koenig and W.T. Keeton, eds. Springer-Verlag, pp. 283-294.

A new technique for studying the orientation of free-flying migrants following experimental manipulation is described. Birds are taken aloft, rereleased at migratory altitudes, and their flight departures accurately plotted by tracking radar.

Experiments on the relative importance of different cue systems in the spring migratory orientation of White-throated Sparrows suggested: (1) Sparrows rapidly selected appropriate, straight, migratory tracks when released under clear night skies or during periods of sunset glow. (2) Under total overcast sparrows still able to select meaningful headings although with much less accuracy. They frequently adopted a sinusoidal, "zigzag" flight strategy under these conditions. (3) Landmark cues of the Atlantic coastline were used minimally if at all by the migrating sparrows.