The noise produced by our everyday devices are disrupting the internal compass of migratory birds. When exposed to weak electromagnetic fields, birds flying at night over urban areas lose their sense of migratory direction. For decades, we’ve debated whether or not electric or magnetic fields affect human health, and this study reveals the stark effect our electronics use have on the function of an entire sensory system in another animal.
Many night-migratory songbirds rely on Earth’s weak magnetic field to orient themselves on their migration paths. But everything we plug in makes electromagnetic noise. "If you could sense this electromagnetic noise, it would probably be like some kind of rock concert going on all the time," Henrik Mouritsen from University of Oldenburg explains in this great video (below).
To see if birds' magnetic compass is affected by human-generated, low-level electromagnetic fields, Mouritsen and colleagues exposed European robins (Erithacus rubecula) to the background electromagnetic noise that’s present in wooden huts at the University of Oldenburg campus. When exposed to weak fields like those produced by AM radio signals and various electronic equipment (like the little tags that stores put on clothing), the bird’s couldn’t orient themselves using their magnetic compass. They become kind of clueless about where they're supposed to go, and they start scratching their enclosures in all directions.
However, they regained their magnetic orientation capabilities when the researchers electrically grounded the huts and covered them with aluminum screens, which passed electromagnetic noise into the land below. This lessened the artificial electromagnetic pollution in frequencies ranging from 50 kilohertz to 5 megahertz. By reducing the noise intensity by about two orders of magnitude, they basically left Earth’s magnetic field unaffected.
But (poor birds), when the team removed the grounding or when they generated broadband electromagnetic noise inside the screened and grounded huts, the birds lost their magnetic orientation capabilities, again. To be extra sure, the researchers repeated these double-blind tests over the course of seven years with successive generations of students.
However, for all that, it’s not from cellphones or power lines. This offending electromagnetic noise can’t be attributed those signals. Additionally, the magnetic component is much weaker than the lower limits of exposure recommended by the World Health Organization.
Fortunately, European robins don’t have to navigate using Earth’s magnetic fields, Science explains: Their manetosense deactivates when it might lead them astray. Their various navigation systems and backup systems include using the sun, other stars, or landmarks. But as Mouritsen says to Nature: “If birds can’t use one of their most significant compasses when they are in towns, what effect will that have on survival?” Perhaps we need to find ways to stop using that part of the electromagnetic spectrum.
The work was published in Nature this week.
Images: Henrik Mouritsen
Video: Nature Video