Sensitivity threshold of avian magnetic compass to oscillating magnetic field is species-specific

One of the most unusual features of the avian magnetic compass is its sensitivity to weak oscillating magnetic fields (OMF) in the radiofrequency range. This effect, observed earlier in numerous experiments in European robins Erithacus rubecula and garden warblers Sylvia borin, is usually associated with the radical-pair magnetoreception in the eye, which is the mainstream biophysical model of the avian magnetic compass. We studied the effect of OMF on the orientation behavior of a long-distance migrant, the pied flycatcher Ficedula hypoleuca. The OMF with an amplitude of 190 nT disoriented pied flycatchers, similarly to the species studied earlier. However, the application of OMP with an amplitude of 17 nT did not lead to disorientation in pied flycatchers when tested in round arenas: the birds showed their correct season-specific migratory direction. This finding is in stark contrast with previous results, obtained in garden warblers at exactly the same place and under the same conditions: garden warblers were disoriented by OMF which was an order of magnitude weaker. Moreover, the threshold of sensitivity to OMF amplitude in pied flycatchers is found to be higher than that in both species previously studied, the European robin and the garden warbler. We discuss the variable sensitivity of avian compass to OMF in the context of migration ecology of two long-distance African migrants, the pied flycatcher and garden warbler, and the short distance migrant, the European robin.