Scientists have known for decades that migratory birds orient themselves using the Earth’s magnetic field in order to fly in the right direction. Now, German researchers have documented for the first time that man-made electromagnetic radiation interferes with these birds’ internal compasses.
The phenomenon was discovered by Henrik Mouritsen, a professor of neurosensory sciences at the University of Oldenburg , and his colleagues, who had been studying migratory birds—specifically, the European robin—since the early 2000s to determine which part of the brain is used by a migratory bird when aligning itself to the geomagnetic field.
Typically, scientists studying magnetoreception test birds’ navigation abilities in so-called orientation cages often set up in wooden huts at rural sites far away from urban areas. Thermal paper placed on the walls of these funnel-shaped cages records the scratches the birds’ feet make as they scrabble upward in an attempt to escape. In the absence of other navigational cues such as the sun and stars, the birds will orient to the Earth’s magnetic field and take off towards the north, marking the paper as they do so.
However, in 2002 Mouritsen moved his research to the University of Oldenburg, which is located in a city of around 160,000 people. Once there, the robins’ behavior changed.
“We were surprised when robins kept in wooden huts on the Oldenburg University campus were unable to use their magnetic compass,” Mouritsen recounted. “The birds basically jumped in random directions every spring and autumn for three years.”
The scientists altered a number of factors to no avail, including the robins’ food, their cages, the light and the daylight cycle. Finally, a graduate student, Nils-Lasse Schneider, suggested covering the huts and the cages they contained with sheets of aluminum to form a Faraday cage. This did not affect the Earth’s magnetic field influence, but shielded against weaker electromagnetic interference, which Mouritsen calls “electrosmog.” With this solution, the birds’ orientation ability returned.
“Our measurements of the interferences indicated that we had accidentally discovered a biological system that is sensitive to anthropogenic electromagnetic noise generated by humans in the frequency range up to five megahertz,” Mouritsen said. Surprisingly, he noted, the intensity of the interference was below the limits defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the World Health Organization (WHO).
During an ensuing seven-year investigation, Mouritsen and his team conducted numerous experiments and double-blind studies in order to collect reliable evidence of the observed effect. They discovered that as soon as the grounding of the screens was disconnected or deliberate electromagnetic interference was created inside the Faraday cage, the birds’ magnetic orientation ability was immediately lost again. Furthermore, the researchers found that the disruptive effects were generated by electromagnetic fields that cover a much broader frequency range at a much lower intensity than previous studies had suggested. As expected, the interference is significantly weaker in rural areas and stronger near locations with a high concentration of electronic devices.
“Thus, the effect of anthropogenic electromagnetic noise on bird migration is localized,” Mouritsen said. “However these findings should make us think—both about the survival of migratory birds as well as about the potential effects for human beings, which have yet to be investigated.”
The related study, “Anthropogenic Electromagnetic Noise Disrupts Magnetic Compass Orientation in a Migratory Bird,” is published in the online journal Nature. In addition to Mouritsen and Schneider, contributing authors include Svenja Engels, Nele Lefeldt, Christine Maira Hein, Manuela Zapka, Andreas Michalik, Dana Elbers, Achim Kittel and P.J. Hore.
