No apparent effect of anthropogenic electromagnetic radiation on the migratory behaviour of wild songbirds

Abstract

Low anthropogenic electromagnetic radiation, also known as “electromagnetic noise” or “electrosmog”, disturbs magnetic compass orientation in migrant songbirds under laboratory conditions. Since electric devices continuously emit equally low electromagnetic noise wherever humans live, it is a biologically highly relevant debated, yet still unsolved question of worldwide importance, whether electromagnetic noise affects the migratory behaviour of free-flying migrant birds in the wild. If so, ecological consequences were global and had wide-ranging implications from animal conservation to human health issues. Therefore, we conducted field experiments to assess the potential after-effects of electromagnetic noise on wild night-migratory songbirds. Similar to the laboratory experiments, we exposed European Robins (Erithacus rubecula) and Northern Wheatears (Oenanthe oenanthe) to electromagnetic radiation, but released the birds afterwards to observe a potential after-effect in their migratory behaviour via radio-tracking. Additionally, we measured birds’ migratory motivation in another experiment. We found no biological relevant effects of electromagnetic radiation on the migratory motivation, and no after-effects on the probability to resume migration, the departure timing within the night, their initial and continued (~50 km) flight direction. However, Wheatears in the electromagnetic noise-exposed group departed significantly later than the controls. As the difference in timing was only 30 seconds in median, in comparison to several hours of nocturnal migration time, we consider this effect as biologically irrelevant. Nevertheless, it shows that these birds put more weight on accuracy in their migratory decision than on speed, when sensing is disturbed or no information form the Earth’s magnetic field available, which is in line with evidence-accumulation-theory. Birds were either able to detect the magnetic field directly after electromagnetic noise exposure or switched to alternative compass systems. We want to highlight that finding no after-effect in our study design does not mean that this man-made factor might not affect migrating birds in other circumstances.