Food intake and fuel deposition in a migratory bird is affected by multiple as well as single-step changes in the magnetic field
2008
SUMMARY Recent studies have shown that migratory thrush nightingales ( Luscinia
luscinia ) experimentally treated with multiple changes of the magnetic
field simulating a journey to their target stopover area in northern Egypt,
increased fuel deposition as expected in preparation to cross the Sahara
desert. To investigate the significance of food intake on the body mass
changes observed, in the work described here we analysed food intake of the
nightingales under study in those earlier experiments. Furthermore, to study
whether a single change in the magnetic field directly to northern Egypt is
sufficient to provide information for fuelling decisions, we performed a new
experiment, exposing thrush nightingales trapped in Sweden, directly to a
magnetic field of northern Egypt. Our results show that an experimentally
induced magnetic field of northern Egypt, close to the barrier crossing,
triggers the same response in fuel deposition as experiments with multiple
changes of the magnetic field simulating a migratory journey from Sweden to
Egypt, suggesting that migratory birds do not require successive changes in
field parameters to incorporate magnetic information into their migratory
program. Furthermore, irrespective of experimental set up (single or multiple
changes of the magnetic field parameters) increase in food intake seems to be
the major reason for the observed increase in fuelling rate compared with
control birds, suggesting that geomagnetic information might trigger hormonal
changes in migratory birds enabling appropriate fuelling behaviour during
migration.
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