The traffic reports on AM radio might help humans navigate, but the electromagnetic waves they travel on could have the opposite effect on birds. A 7-year investigation has discovered that radio waves disrupt the piloting systems of migratory European robins. The work, experts say, provides convincing evidence that such transmissions can alter animal behavior.
For decades, people have feared that cellphones, power lines, and other sources of electromagnetic radiation might harm both human health and nature. But don’t fret. Your cellphones are still safe to use in the wild. “Modern-day charlatans will try to exploit this study to claim that cellphone radiation causes damage, but it’s not screwing up the robins,” says geobiologist Joseph Kirschvink of the California Institute of Technology in Pasadena, who was not involved in the study. “It's telling them to use a different sense.”
European robins, like many migratory birds, can navigate via Earth’s magnetic fields —but they don’t have to. Scientists have known for 30 years that robins’ magnetosense deactivates when it might lead them astray, for instance if they hit a spot where Earth’s geomagnetic field dramatically changes strength. Low-intensity radio waves now join this group of negative triggers.
Biologists at the University of Oldenburg in Germany stumbled upon the phenomenon by accident in 2004 while they were testing a basic feature of European robin behavior. During the spring and autumn, the birds’ urge to travel is so strong that captured individuals will reflexively start jumping in the direction of their migration, even scratching up the bottom of their cages. But when the robins were held in wooden huts on campus, they were suddenly clueless as to which way they were supposed to be going.
So the researchers started experimenting to see why the birds’ compasses appeared to have shut off. Change their food? No difference. Tweak their sleep cycles with artificial lighting? Nada. Finally, they started wondering if the magnetic fields produced by electronic devices on campus might be the culprit.
To find out, the researchers installed aluminum wallpaper inside the birds’ wooden huts. The metal sidings were linked by means of wires to metal rods buried in the dirt outside. When electromagnetic noise struck the aluminum, it was soaked up and passed into the land. Known as “grounding,” this canceled out the electromagnetic noise coming through the huts’ walls, leaving a signal from only Earth’s magnetic field. After the screens were built, the robins aligned in the right direction , the team reports online today in Nature. But when the shields were switched off, the birds became disoriented again.
Given the skepticism surrounding prior research into electromagnetic noise and animal habits, the project leaders used double-blind experiments to replicate the finding. Undergraduate and graduate volunteers ran the trials. Some worked in wooden huts with the shields turned on, while others had them off—but to eliminate bias, the students didn’t know who was working where.
“We added a number of securities to protect ourselves from wishful thinking,” says neurosensory biologist Henrik Mouritsen of the University of Oldenburg, who led the study. “The conditions were repeated with different generations of students, and experiments were blinded on all levels.”
Artificially reintroducing magnetic fields into a screened hut allowed the researchers to pinpoint possible sources of the misguiding noise. The most disorienting electromagnetic noise had frequencies matching those produced by AM radio stations and small devices like electronic article surveillance—those little magnetic tags for clothing at department stores. This is 1000 times less powerful than the frequencies emitted by cellphones and 400 times higher than those produced by power lines. Moving the birds to a rural location without electronic noise immediately restored their navigation skills.
European migratory bird populations are declining. Though habitat destruction is the main suspect, the findings raise questions as to whether humanmade electromagnetic pollution from radio stations and home electronics is a general problem across Europe, or if this phenomenon is specific to Oldenburg.
“I just wonder where this strong field originates,” says retired zoologist Roswitha Wiltschko, who co-discovered the avian magnetic compass with her husband Wolfgang in the 1970s and who was not involved in the work. “We were doing these experiments in the central district of Frankfurt, a major city, and we never had problems with magnetic fields disrupting the orientation of our birds.” Wiltschko feels the study is “really well done” but thinks more research is needed before claiming that this is a general occurrence.
If it is, the effect should be short-ranged and limited to within 5 to 10 km of AM stations, says Kirschvink, who thinks that birds may have evolved this off switch for their magnetic compass long before Guglielmo Marconi invented the radio in order to combat radiation fluxes created by the sun’s activity.