Magnetobiology & Magnetoreception [Resources]

Extremely weak simple oscillating magnetic fields (MF), when added to the local geomagnetic field have been observed to disrupt the European Robin's orientation (Ritz et. al. 2009), this disruption has been shown to operate at MF intensities as low 15 nanotesla. To put that intensity in perspective, that's 3000 times weaker than the Earth's local geomagnetic field of 46 microtelsa.

Trying to reproduce biological effects of these hyperweak MF is proving very very difficult. In this study, only very specific MF oscillating frequencies and intensities, when combined with very specific static MF intensity, and specific frequencies of light could produce the effect. Even then, the addition of these hyperweak oscillating MF's could do nothing more than produce a blunt 'disruption' of some unknown mechanism which is used by the Robin to orientate itself.

It's a great example of simple patterned hyperweak external MF's affecting a biological organisms behavior, whilst in the presence of other stronger MF's.

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Kavokin et al 2014 has now replicated Ritz's work (above), but with garden warblers, at a different time of year, and using different equipment.

Their results indicate that garden warblers can select and maintain broadly correct migratory orientation on the basis of magnetic cues alone, and that this ability can be transiently damaged by weak 190 nanoTesla oscillating (1.4MHz) magnetic fields (MF) - these are hundreds of times weaker than the earths local geomagnetic field.

It now seems certain that organics can detect hyperweak MF's despite the presence of stronger MF's, and that nature has evolved some way of doing so, that we as yet do not understand.

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Engals et al 2014 has now shown hyper-weak magnetic field (MF) effects on the European Robin's navigation at a broader range of frequencies, and at an even lower MF intensity of 1 nanoTesla. To put that intensity in perspective that's 40,000 times lower than the earth's local geomagnetic field, and is at least an order of magnitude lower than previous studies.

Although this intensity is still approximately two orders of magnitude above the average MF of the brain, it's really quite close now.

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A very exciting study on the spontaneous alignment of snapping turtles exposed to hyper-weak magnetic fields (MF) between about 30 - 50 nanoTesla. I think its incredibly exciting...

Quote: "...What is arguably the most important finding from these experiments, however, is that in addition to the well-studied use in goal-directed orientation, the magnetic field appears to play an important, and as yet poorly understood role, in encoding spatial information in the animal’s immediate surroundings..."

Landler et al 2015 "Spontaneous Magnetic Alignment by Yearling Snapping Turtles: Rapid Association of Radio Frequency Dependent Pattern of Magnetic Input with Novel Surroundings"

Abstract
We investigated spontaneous magnetic alignment (SMA) by juvenile snapping turtles using exposure to low-level radio frequency (RF) fields at the Larmor frequency to help characterize the underlying sensory mechanism.

Turtles, first introduced to the testing environment without the presence of RF aligned consistently towards magnetic north when subsequent magnetic testing conditions were also free of RF ( ‘ RF off ! RF off ’ ), but were disoriented when subsequently exposed to RF ( ‘ RF off ! RF on ’ ). In contrast, animals initially introduced to the testing environment with RF present were disoriented when tested without RF ( ‘ RF on ! RF off ’ ), but aligned towards magnetic south when tested with RF (‘ RF on ! RF on ’).

Sensitivity of the SMA response of yearling turtles to RF is consistent with the involvement of a radical pair mechanism. Furthermore, the effect of RF appears to result from a change in the pattern of magnetic input, rather than elimination of magnetic input altogether, as proposed to explain similar effects in other systems/organisms. The findings show that turtles first exposed to a novel environment form a lasting association between the pattern of magnetic input and their surroundings. However, under natural conditions turtles would never experience a change in the pattern of magnetic input. Therefore, if turtles form a similar association of magnetic cues with the surroundings each time they encounter unfamiliar habitat, as seems likely, the same pattern of magnetic input would be associated with multiple sites/localities. This would be expected from a sensory input that functions as a global reference frame, helping to place multiple locales (i.e., multiple local landmark arrays) into register to form a global map of familiar space.