Autumn migratory fuelling: a response to simulated magnetic displacements in juvenile wheatears, Oenanthe oenanthe

Northern magnetic displacements trigger endogenous fuelling responses in a naive bird migrant

“…The lower body masses of the other treatments probably mirror the relatively small fuel loads recorded in wheatears throughout Europe (Delingat et al 2006). The fact that wheatears did not increase their body mass in south-western magnetic fields, even though they were exposed to unexpected magnetic fields, suggests that the higher body mass shown in treatment W (Boström et al 2010) is a specific response to the simulated northern displacement experienced by the birds. Since there was no difference in wing length between years, all the birds could be expected to be able to fly approximately the same distance at any given body mass.…”

“…One group was kept in the ambient magnetic field at the experimental site for comparison ('treatment Swe '). The results were compared to the previous study (performed in 2007;Boström et al 2010). There was no difference in wing length between years (independent samples t test, t 1, 22 0−0.17, p00.87).…”

“…In an earlier study, we reported that wild-caught Swedish juvenile wheatears experiencing a magnetic, but not geographic displacement to the west of their natural migration route (hereafter called 'treatment W ') increased more in body mass than individuals experiencing a simulation of their population-specific migration route through western Europe ('treatment mig ') (Boström et al 2010). The magnetic parameters used for the western displacement, however, also translate into a northern magnetic field relative to the experimental site (i.e., stronger total field intensity and steeper inclination angle; Fig.…”

“…Treatment Swe birds were kept in the ambient magnetic field at Tovetorp and treatment SW birds were displaced to Atlantic 2 and 3. In our previous experiment, the displaced wheatears were displaced to Atlantic 1 and 2 (Boström et al 2010). The hatched lines show the total field intensity (micro Tesla) and the solid lines show the inclination (in degrees).…”

“…The birds were brought to Stensoffa Ecological Field Station (55°42′ N, 13°25′ E) where they were kept individually in outdoor aviaries for 30 days before transportation to the experimental site. We used the same method and experimental setup as in Boström et al (2010), but excluded the northernmost position in the treatment (Atlantic 1 in Boström et al 2010) and only used magnetic parameters corresponding to south-western displacements ('treatment SW '; Fig. 1 and Table 1).…”