Avian magnetic compass can be tuned to anomalously low magnetic intensities

Abstract

The avian magnetic compass works in a fairly narrow functional window around the intensity of the local geomagnetic field, but adjusts to intensities outside this range when birds experience these new intensities for a certain time. In the past, the geomagnetic field has often been much weaker than at present. To find out whether birds can obtain directional information from a weak magnetic field, we studied spontaneous orientation preferences of migratory robins in a 4 mT field (i.e. a field of less than 10 per cent of the local intensity of 47 mT). Birds can adjust to this low intensity: they turned out to be disoriented under 4 mT after a pre-exposure time of 8 h to 4 mT, but were able to orient in this field after a total exposure time of 17 h. This demonstrates a considerable plasticity of the avian magnetic compass. Orientation in the 4 mT field was not affected by local anaesthesia of the upper beak, but was disrupted by a radiofrequency magnetic field of 1.315 MHz, 480 nT, suggesting that a radical-pair mechanism still provides the directional information in the low magnetic field. This is in agreement with the idea that the avian magnetic compass may have developed already in the Mesozoic in the common ancestor of modern birds.

Upper bound on the biological effects of 50/60 Hz magnetic fields mediated by radical pairs

“…We cannot begin to imagine what that aspect might be except to note a possibly related observation. Migratory birds are prevented from using their magnetic compass by extraordinarily weak broadband radiofrequency noise (60,(109)(110)(111)(112)(113)(114)(115) the predicted effects of which are far too small to be consistent with our current understanding of radical pair spin dynamics (116,117). It is possible, therefore, that a deeper understanding of the mechanism of avian magnetoreception will bring new insights into the risks associated with exposure to weak environmental 50/60 Hz magnetic fields.…”

Magnetoreception in birds: the effect of radio-frequency fields

“…An interference with the photo-activation of cryptochrome would become visible in an immuno-histological study exposing birds to radio-frequency fields and then marking the activated Cry1a with immuno-staining [17]. If the compass mechanism is driven outside its functional range, birds would be expected to overcome the disruptive effects if they were exposed to a radio-frequency field prior to testing [16], just as exposure to weaker or stronger static fields allows birds to adjust the functional window of their magnetic compass to these intensities and regain their orientation ability [1,18,19]. We also checked for immediate after-effects of exposure to radio-frequency fields.…”

Magnetically induced behaviour of ferritin corpuscles in avian ears: can cuticulosomes function as magnetosomes?

“…, and also by microtesla long-term exposure [1,2]. Therefore, we may assume the existence of innervated magnetically sensitive sensors for detection of geomagnetic field strength or direction in diverse animal species.…”