Soaring Migration of the Common Crane Grus grus Observed by Radar and from an Aircraft

Migrating Crane flocks were tracked over southern Sweden with a tracking radar and an aircraft. Air speeds and rates of climb in thermals were recorded, and behaviour was observed. The Cranes flew faster than soaring theory would predict, and also used varying amounts of muscle power on the interthe...

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Bibliographic Details
Published in:Ornis Scandinavica 1979-01, Vol.10 (2), p.241-251
Main Authors: Pennycuick, Colin J., Alerstam, Thomas, Larsson, Bertil
Format: Article
Language:English
Subjects:
Aerial locomotion
Aircraft
Animal migration behavior
Basal metabolism
Birds
Gliding
Radar
Radar tracking
Vehicular flight
Wind velocity
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Summary:Migrating Crane flocks were tracked over southern Sweden with a tracking radar and an aircraft. Air speeds and rates of climb in thermals were recorded, and behaviour was observed. The Cranes flew faster than soaring theory would predict, and also used varying amounts of muscle power on the interthermal glides. We estimate that their use of thermals and "partially powered" glides substantially reduced the energetic cost of flying unit distance, but at the expense of a reduction in average speed. The behaviour required for soaring is elaborate, and the selection pressures for and against it are discussed. Crane flocks were seen to split up and recombine in a way which suggested that they were not stable social units.
ISSN:0030-5693
DOI:10.2307/3676068