Titolo Magnetic orientation of garden warblers (Sylvia borin) under 1.4 MHz radiofrequency magnetic field.
Rivista J R Soc Interface.
Numero 2014 Aug 6;11(97):20140451. doi: 10.1098/rsif.2014.0451.
Autori Kavokin K1, Chernetsov N2, Pakhomov A3, Bojarinova J4, Kobylkov D2, Namozov B5.
Enti 1St Petersburg State University, St Petersburg, Russia, A.F. Ioffe Physical Technical Institute, St Petersburg, Russia
2St Petersburg State University, St Petersburg, Russia Biological Station Rybachy, Zoological Institute, Russia.
3Biological Station Rybachy, Zoological Institute, Russia Moscow State University, Moscow, Russia.
4St Petersburg State University, St Petersburg, Russia.
5A.F. Ioffe Physical Technical Institute, St Petersburg, Russia.
Link http://www.ncbi.nlm.nih.gov/pubmed/24942848
Accesso  

Abstract

Descriviamo gli esperimenti sull'orientamento dei passeri migratori, il Beccafico (Sylvia borin), durante il periodo di migrazione autunnale sul Courish Spit, Paesi Baltici orientali. Gli uccelli, dentro gabbie sperimentali, privi di informazioni visive, hanno mostrato di possedere la desiderata direzione di volo stagionalmente appropriata rispetto al meridiano magnetico. Un campo a radiofrequenza debole (190 nT a 1.4 MHz) ha fatto cessare questa capacità di orientamento. Tali risultati possono essere considerati come una replica indipendente di esperimenti precedenti, eseguiti dal gruppo di R. e W. Wiltschko con pettirossi europei (Erithacus rubecula) (ndr: http://www.ncbi.nlm.nih.gov/pubmed/25540238). La confermata eccezionale sensibilità della bussola magnetica degli uccelli a campi in radiofrequenza nelle bande dei MegaHertz richiede una revisione di una delle principali teorie della magnetoricezione, il modello coppia-radicali della bussola magnetica degli uccelli.

 

 

Estratti:

"... birds were shown to have at least three mechanisms of direction finding, namely the sun compass [3,4], stellar compass [5–8] and the magnetic compass [9]. The latter is especially interesting, because the well-documented existence of the magnetic compass in birds remains one of few unambiguous demonstrations of the elusive magnetic sense of animals, the physical and physiological origins of which are still unclear [10]. Based, again, mainly on laboratory experiments with birds, two theoretical models of magnetoreception in terrestrial animals were singled out as the most viable: one involving magnetic nanocrystals of iron oxides [11] and the other based on magneto-sensitive photochemical reactions in the eye [12,13] (the radical-pair model, RPM) ....

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].

Here, we report the results of our experiments which were aimed to independently replicate the claims that small-amplitude RF field disrupts magnetic orientation in migratory songbirds ...

We tested a total of 19 garden warblers in NMF and in OMF. One bird never showed directed and sufficiently concentrated orientation in OMF, in spite of being tested five times. Unfortunately, we managed to test only eight garden warblers in RMF before the end of September when migratory activity and orientation sharply decreased ....

Behaviour of birds in our experiments strongly suggests that in the stationary field, both the natural one and the one rotated 120° in the horizontal plane, garden warblers used the magnetic field for their orientation, because they were denied access to celestial orientation cues and showed a predictable response to the rotation of magnetic North. Our results thus indicate that (i) garden warblers can select and maintain broadly correct migratory orientation on the basis of magnetic cues alone; (ii) this ability is damaged by weak (190 nT) OMFs; (iii) this impairment is transient, i.e. when the same birds are again tested in a stationary magnetic field, they orient successfully. Thus, our results independently replicate reports of the group of R. and W. Wiltschko on the disruptive effect of RF magnetic fields on the magnetic compass of migratory songbirds [21,22,24] ....

As discussed above, the high sensitivity of the birds' magnetic compass to RF fields, found in [21,22,24] and now confirmed by us, is difficult to explain within the existing radical-pair theory ....

It may be argued that we tested our birds only for a resonance effect and made no tests in an off-resonance or broadband RF oscillating field; therefore, we cannot distinguish between a specific Zeeman resonance effect of a relatively weak (190 nT) RF field and a putative effect of an off-resonance or broadband RF field of the same intensity. However, as emphasized in the Introduction, neither the resonance nor off-resonance RF field effect have so far found a satisfactory theoretical explanation. Our main point is that a RF field of roughly the same amplitude as used in the experiments of [22,24] is indeed able to disrupt the magnetic orientation of a migratory songbird, and thus it is very unlikely that the findings of aforementioned studies resulted from some systematic error or a hidden flaw of the experimental procedure. This, in its turn, means that the radical-pair theory of avian magnetoreception in its current form may need revision to account for this RF field effect.

More experimental work is needed to refine the spectral width of the observed Zeeman resonance in the sensitivity of the avian compass to RF fields [22] and to verify the reported sensitivity threshold at the exact resonance (about 15 nT). Only after obtaining these data (which may take several field seasons), one would be able to obtain a reliable experimental estimate of the spin lifetimes in the radical pair or whatever physical system is responsible for the compass magnetoreception of birds. However, already these previous results demand the renewed attention of theoreticians to the physical and chemical models of magnetoreception."