Key points are not available for this paper at this time.
Colin J. Pennycuick, Thomas Alerstam, Bertil Larsson, Soaring Migration of the Common Crane Grus grus Observed by Radar and from an Aircraft, Ornis Scandinavica (Scandinavian Journal of Ornithology), Vol. 10, No. 2 (1979), pp. 241-251
Pennycuick et al. (1979) studied this question.
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