Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird.

Electromagnetic noise is emitted everywhere humans use electronic devices. For decades, it has been hotly debated whether man-made electric and magnetic fields affect biological processes, including human health. So far, no putative effect of anthropogenic electromagnetic noise at intensities below the guidelines adopted by the World Health Organization has withstood the test of independent replication under truly blinded experimental conditions. No effect has therefore been widely accepted as scientifically proven. Here we show that migratory birds are unable to use their magnetic compass in the presence of urban electromagnetic noise. When European robins, Erithacus rubecula, were exposed to the background electromagnetic noise present in unscreened wooden huts at the University of Oldenburg campus, they could not orient using their magnetic compass. Their magnetic orientation capabilities reappeared in electrically grounded, aluminium-screened huts, which attenuated electromagnetic noise in the frequency range from 50 kHz to 5 MHz by approximately two orders of magnitude. When the grounding was removed or when broadband electromagnetic noise was deliberately generated inside the screened and grounded huts, the birds again lost their magnetic orientation capabilities. The disruptive effect of radiofrequency electromagnetic fields is not confined to a narrow frequency band and birds tested far from sources of electromagnetic noise required no screening to orient with their magnetic compass. These fully double-blinded tests document a reproducible effect of anthropogenic electromagnetic noise on the behaviour of an intact vertebrate.

Night-migratory songbirds possess a magnetic compass in both eyes.

Previous studies on European robins, Erithacus rubecula, and Australian silvereyes, Zosterops lateralis, had suggested that magnetic compass information is being processed only in the right eye and left brain hemisphere of migratory birds. However, recently it was demonstrated that both garden warblers, Sylvia borin, and European robins have a magnetic compass in both eyes. These results raise the question if the strong lateralization effect observed in earlier experiments might have arisen from artifacts or from differences in experimental conditions rather than reflecting a true all-or-none lateralization of the magnetic compass in European robins. Here we show that (1) European robins having only their left eye open can orient in their seasonally appropriate direction both during autumn and spring, i.e. there are no strong lateralization differences between the outward journey and the way home, that (2) their directional choices are based on the standard inclination compass as they are turned 180° when the inclination is reversed, and that (3) the capability to use the magnetic compass does not depend on monocular learning or intraocular transfer as it is already present in the first tests of the birds with only one eye open.

Robins have a magnetic compass in both eyes.

Arising from W. Wiltschko et al. 419, 467-470 (2002); Wiltschko et al. replyThe magnetic compass of migratory birds is embedded in the visual system and it has been reported by Wiltschko et al. that European Robins, Erithacus rubecula, cannot show magnetic compass orientation using their left eye only. This has led to the notion that the magnetic compass should be located only in the right eye of birds. However, a complete right lateralization of the magnetic compass would be very surprising, and functional neuroanatomical data have questioned this notion. Here we show that the results of Wiltschko et al. could not be independently confirmed using double-blind protocols. European Robins can perform magnetic compass orientation with both eyes open, with the left eye open only, and with the right eye open only. No clear lateralization is observed.

Night-migratory garden warblers can orient with their magnetic compass using the left, the right or both eyes.

Several studies have suggested that the magnetic compass of birds is located only in the right eye. However, here we show that night-migrating garden warblers (Sylvia borin) are able to perform magnetic compass orientation with both eyes open, with only the left eye open and with only the right eye open. We did not observe any clear lateralization of magnetic compass orientation behaviour in this migratory songbird, and, therefore, it seems that the suggested all-or-none lateralization of magnetic compass orientation towards the right eye only cannot be generalized to all birds, and that the answer to the question of whether magnetic compass orientation in birds is lateralized is probably not as simple as suggested previously.

Multistable perception: when bottom-up and top-down coincide.

During prolonged observation of an ambiguous figure sudden perceptual reversals occur, while the stimulus itself stays unchanged. There is a vivid debate about whether bottom-up or top-down mechanisms underlie this phenomenon. In the present study, we investigated the interrelation of two experimental factors: volitional control and discontinuous stimulus presentation. Both factors strongly modulate the rate of perceptual reversals and each is attributed either as top-down or bottom-up. We found that participants can apply specific strategies to volitionally increase and/or decrease the stability duration of each of the possible percepts according to the experimental instructions. When attempts of volitional control are combined with discontinuous stimulus presentation the effects are fully additive. Our results indicate that perceptual reversals can originate from different neural mechanisms on different time scales.