Very weak oscillating magnetic field disrupts the magnetic compass of songbird migrants

Abstract

Previously, it has been shown that long-distance migrants, garden warblers (), were disoriented in the presence of narrow-band oscillating magnetic field (1.403 MHz OMF, 190 nT) during autumn migration. This agrees with the data of previous experiments with European robins (). In this study, we report the results of experiments with garden warblers tested under a 1.403 MHz OMF with various amplitudes (∼0.4, 1, ∼2.4, 7 and 20 nT). We found that the ability of garden warblers to orient in round arenas using the magnetic compass could be disrupted by a very weak oscillating field, such as an approximate 2.4, 7 and 20 nT OMF, but not by an OMF with an approximate 0.4 nT amplitude. The results of the present study indicate that the sensitivity threshold of the magnetic compass to the OMF lies around 2-3 nT, while in experiments with European robins the birds were disoriented in a 15 nT OMF but could choose the appropriate migratory direction when a 5 nT OMF was added to the stationary magnetic field. The radical-pair model, one of the mainstream theories of avian magnetoreception, cannot explain the sensitivity to such a low-intensity OMF, and therefore, it needs further refinement.

No evidence for the use of magnetic declination for migratory navigation in two songbird species

“…It was identical for the control and experimental conditions; furthermore, at the rural testing site on the Courish Spit the anthropogenic noise is likely to have been very low, as suggested e.g. by the functional magnetic compass observed in garden warblers when tested under control conditions at the same site [24,25].…”

“…The birds were provided with food (mealworms) and water ad libitum. We did not measure the background electromagnetic noise level, which is important for the functionality of the magnetic compass in European robins and garden warblers [23,24]. It was identical for the control and experimental conditions; furthermore, at the rural testing site on the Courish Spit the anthropogenic noise is likely to have been very low, as suggested e.g.…”

Learned and spontaneous magnetosensitive behaviour in the Roborovski hamster (Phodopus roborovskii)

“…Previously, RF intensities of 48–400 nT were shown to influence animal magnetic orientation behaviour (for review see Hiscock et al., ). Recent studies demonstrated an effect of much weaker (anthropogenic) RF fields in the low MHz range with strengths of about 10 nT (Engels et al., ; Pakhomov et al., ), and even lower intensities of broadband RF noise of 1 nT are discussed to influence magnetosensitive abilities of birds (Engels et al., ). In our study, intensities of 0.3 nT up to 10 nT at the highest peak (0.4 MHz) (control condition) seemed to have no influence on the magnetic orientation of Roborovski hamsters, but additional slight increases of 0.3–2 nT, when the coil system was switched on, seemed to disturb the hamster's orientation abilities.…”

Magnetoreception in birds

“…This applies to migrants during migratory orientation [21–24] as well as to directionally trained non-migrants such as Domestic Chickens [25] and Zebra Finches [26]. The Larmor frequency, that is, the frequency of the electron, proved most effective and disrupts orientation at very low intensities [27]; this has been independently confirmed by [23,28]. Reports of the opposite [24] are inconclusive because of methodological short-comings (use of metallic test cages that not only shield but also reflect and distort radiofrequency fields so that the conditions become undefined).…”