Magnetic compass orientation of migratory birds in the presence of a 1.315�MHz oscillating field

Abstract

The radical pair model of magnetoreception predicts that magnetic compass orientation can be disrupted by high frequency magnetic fields in the Megahertz range. European robins, Erithacus rubecula, were tested under monochromatic 565 nm green light in 1.315 MHz fields of 0.48 microT during spring and autumn migration, with 1.315 MHz being the frequency that matches the energetic splitting induced by the local geomagnetic field. The birds' responses depended on the alignment of the oscillating field with respect to the static geomagnetic field: when the 1.315 MHz field was aligned parallel with the field lines, birds significantly preferred northerly directions in spring and southerly directions in autumn. These preferences reflect normal migratory orientation, with the variance slightly increased compared to control tests in the geomagnetic field alone or to tests in a 7.0 MHz field. However, in the 1.315 MHz field aligned at a 24 degrees angle to the field lines, the birds were disoriented in both seasons, indicating that the high frequency field interfered with magnetoreception. These finding are in agreement with theoretical predictions and support the assumption of a radical-pair mechanism underlying the processes mediating magnetic compass information in birds.

Magnetic orientation of garden warblers ( Sylvia borin ) under 1.4 MHz radiofrequency magnetic field

“…15 nT and frequency 1.315 MHz always caused disorientation, while for most cages it was, in fact, off the resonance. 1 The theory of magnetic resonance says that the expected effect of the RF field, in this case, is at least 100 times weaker that one of the strictly resonant RF field; therefore, the required spin relaxation time shifts to utterly unbelievable 0.2 s. A similar estimate (about 1 s) was obtained in reference [25] from the observed effect of a broadband (0.1-10 MHz) RF field with the amplitude of 85 nT [24]. No need to say that any remotely realistic model of the radical pair would give worse sensitivity to the RF field than the 'reference -probe' model considered above.…”

“…It is important to stress that though our experimental protocol was essentially the same as one used in the Wiltschkos' group, there were several notable differences: we worked with a different bird species (garden warblers instead of European robins), in a different season (autumn instead of spring) and used a different type of antenna and electronic equipment. Nevertheless, the basic effect reported in [21,22,24] was reproduced.…”

“…To summarize this long introduction, experimental works [21,22,24] and consequent theoretical studies aimed at their explanation [25,28] have led to a dilemma: either the experiments of the Frankfurt group on the RF field effect upon orientation of European robins were flawed and their results are incorrect, or the RPM in its present form does not correctly reproduce the physics of the bird's magnetic compass. As the RPM is one of the mainstream theories of magnetoreception, and there exists a considerable body of experimental evidence supporting the idea that compass magnetoreception is based on the vision system of birds, independent experimental studies aimed at confirmation or negation of the results of previous studies [21,22,24] are of key importance for the further development of the science of magnetoreception [10].…”

“…As the RPM is one of the mainstream theories of magnetoreception, and there exists a considerable body of experimental evidence supporting the idea that compass magnetoreception is based on the vision system of birds, independent experimental studies aimed at confirmation or negation of the results of previous studies [21,22,24] are of key importance for the further development of the science of magnetoreception [10].…”

Chemical magnetoreception in birds: The radical pair mechanism

“…Such resonances are diagnostic for radical pairs: Magnetite particles of sufficient size to function as a compass are too large to reorient in magnetic fields fluctuating as rapidly as 1 MHz (73,74). Linearly polarized radio frequency fields 100 times weaker than the Earth's field (Ϸ500 nT), with frequencies of 7.0 MHz or 1.315 MHz, are sufficient to disrupt the migratory orientation of caged European robins (75,76). Moreover, disorientation is found when the angle between the Earth's field and the radio frequency field is 24°or 48°, but not when the 2 fields are collinear.…”