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Winklhofer, Michael; Dylda, Evelyn; Thalau, Peter; Wiltschko, Wolfgang; Wiltschko, Roswitha (2013): Avian magnetic compass can be tuned to anomalously low magnetic intensities. In: Proceedings of the Royal Society B - Biological Sciences, Vol. 280, Nr. 1763
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Abstract

The avian magnetic compass works in a fairly narrow functional windowaround the intensity of the local geomagnetic field, but adjusts tointensities outside this range when birds experience these newintensities for a certain time. In the past, the geomagnetic field hasoften been much weaker than at present. To find out whether birds canobtain directional information from a weak magnetic field, we studiedspontaneous orientation preferences of migratory robins in a 4 mu Tfield (i.e. a field of less than 10 per cent of the local intensity of47 mu T). Birds can adjust to this low intensity: they turned out to bedisoriented under 4 mu T after a pre-exposure time of 8 h to 4 mu T, butwere able to orient in this field after a total exposure time of 17 h.This demonstrates a considerable plasticity of the avian magneticcompass. Orientation in the 4 mu T field was not affected by localanaesthesia of the upper beak, but was disrupted by a radiofrequencymagnetic field of 1.315 MHz, 480 nT, suggesting that a radical-pairmechanism still provides the directional information in the low magneticfield. This is in agreement with the idea that the avian magneticcompass may have developed already in the Mesozoic in the commonancestor of modern birds.