Autumn migratory fuelling: a response to simulated magnetic displacements in juvenile wheatears, Oenanthe oenanthe |
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Authors: | Jannika E Boström Thord Fransson Ian Henshaw Sven Jakobsson Cecilia Kullberg Susanne Åkesson |
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Institution: | (1) Department of Biology, Lund University, Ecology Building, 223 62 Lund, Sweden;(2) Swedish Museum of Natural History, Bird Ringing Centre, Box 50 007, 104 05 Stockholm, Sweden;(3) Department of Physics and Materials Science, Uppsala University, 751 21 Uppsala, Sweden;(4) Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden |
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Abstract: | Recent experiments exposing migratory birds to altered magnetic fields simulating geographical displacements have shown that
the geomagnetic field acts as an external cue affecting migratory fuelling behaviour. This is the first study investigating
fuel deposition in relation to geomagnetic cues in long-distance migrants using the western passage of the Mediterranean region.
Juvenile wheatears (Oenanthe oenanthe) were exposed to a magnetically simulated autumn migration from southern Sweden to West Africa. Birds displaced parallel
to the west of their natural migration route, simulating an unnatural flight over the Atlantic Ocean, increased their fuel
deposition compared to birds experiencing a simulated migration along the natural route. These birds, on the other hand, showed
relatively low fuel loads in agreement with earlier data on wheatears trapped during stopover. The experimental displacement
to the west, corresponding to novel sites in the Atlantic Ocean, led to a simulated longer distance to the wintering area,
probably explaining the observed larger fuel loads. Our data verify previous results suggesting that migratory birds use geomagnetic
cues for fuelling decisions and, for the first time, show that birds, on their first migration, can use geomagnetic cues to
compensate for a displacement outside their normal migratory route, by adjusting fuel deposition. |
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