Migrating swans profit from favourable changes in wind conditions at low altitude |
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Authors: | Marcel Klaassen Jan H Beekman Jari Kontiokorpi Roef J W Mulder and Bart A Nolet |
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Institution: | (1) Centre for Limnology, Netherlands Institute of Ecology, P.O. Box 1299, 3600 BG Maarssen, The Netherlands;(2) Zoological Laboratory, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands;(3) Reinikaisenkatu 5 E 21, 56800 Simpele, Finland |
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Abstract: | Because energy reserves limit flight range, wind assistance may be of crucial importance for migratory birds. We tracked eight Bewick s swans Cygnus columbianus bewickii, using 95-g satellite transmitters with altimeters and activity sensors, during their spring migration from Denmark to northern Russia in 1996. During the 82 occasions where a swan s location was recorded in flight, average flight altitude was 165 m a.s.l. with a maximum of 759 m a.s.l., despite winds often being more favourable at higher altitudes. We also counted Bewick s swans departing from the Gulf of Finland and subsequently passing an observatory in the next major stop-over area 800 km further north in the White Sea, northern Russia, during the springs of 1994, 1995 and 1996. A comparison of these counts with wind data provided evidence for Bewick s swans using favourable changes in wind conditions to embark on migration. Changes in the numbers of birds arriving in the White Sea correlated best with favourable changes in winds in the Gulf of Finland 1 day earlier. Again, migratory volume showed a correlation with winds at low altitudes only, despite wind conditions for the swans being more favourable at high altitudes. We conclude that the relatively large Bewick s swan tends to gear its migration to wind conditions at low altitude only. We argue that Bewick s swans do not climb to high altitudes because of mechanical and physiological limitations with respect to the generation of power for flight and to avoid rapid dehydration.Communicated by F. Bairlein |
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Keywords: | Bewick s swan" target="_blank">gif" alt="rsquo" align="BASELINE" BORDER="0">s swan Cygnus columbianus bewickii Migration Flight altitude Tailwind vector Satellite transmitters |
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