Every autumn, billions of songbirds begin a grueling flight to their wintering spots, guided by built-in navigational tools on trips that can stretch thousands of miles. Now research shows that our love of electrical gizmos may be interfering with the birds’ epic journey.

Electrical gadgets as basic as AM radios scramble the magnetic compass that birds use to navigate dark, cloudy skies, even when the signals from these gadgets are far weaker than levels set to protect human health, according to new experiments. No one knows the precise impact of this human-made interference on birds. But scientists do know that many species of migratory songbirds are declining, and gumming up their compasses could make matters worse.

Electrical appliances “could be a contributing factor that people overlooked in the past,” said one of the study’s authors, Henrik Mouritsen of the University of Oldenburg in Germany. “I’m pretty sure the birds would be better off if their magnetic compasses were not disturbed.”

Mouritsen stumbled across this effect after a long, frustrating campaign to get his research birds to behave. Scientists studying bird migration capitalize on a well-known phenomenon: During migration season, captive birds hop in the direction they’d fly if they were free. During Mouritsen’s years of research at field sites in Denmark, his birds did as they were supposed to do. But after he moved to Oldenberg, Mouritsen couldn’t get his new flock of European robins to face the right way. He changed their food, their cages, the room, the light. No joy. Finally a colleague suggested shielding the birds’ wooden hut with armor-like aluminum plates.

“I thought it was highly unlikely that was going to help,” said Mouritsen, but “we were desperate, trying everything we could to get the basic experiment to work. ... It wasn’t a good situation.”

Despite Mouritsen’s expectations, after the team installed the shielding, the birds obediently turned to point their beaks in the right direction. The plates didn’t block the Earth’s magnetic field, but they had apparently blocked the fuzzy welter of electrical and magnetic “noise” emanating from the countless electrical devices near the hut. This “electrosmog,” as Mouritsen calls the combined electromagnetic fields emitted by an array of appliances, was somehow throwing off the birds’ own magnetic compass.

Aside from AM radio waves, the scientists don’t know what’s responsible. They rule out cellphone signals and power lines, but possible culprits include printers, computers, refrigerators and lights. But the research, reported in the journal Nature, shows that extremely weak fields – weaker than anything harming humans – can cripple a robin’s magnetic system.

The results were so extraordinary that Mouritsen and his team held off publishing their findings for seven years while they ran more tests. But they couldn’t undercut their original results. When a machine generating a weak magnetic field was introduced into the robins’ shielded huts, they stopped facing the right way. When the birds were moved to huts in the countryside, far from electronic equipment, their orienting ability was restored.

The results are “pretty convincing,” said David Dickman of the Baylor College of Medicine, who studies birds’ magnetic sense. “Many birds die every year during the migratory process, and it could be that (electromagnetic noise) is another effect of our society upon nature.”

Mouritsen’s birds could be an exceptional case, said Roswitha Wiltschko of the Goethe University Frankfurt in Germany, who has studied bird migration for decades. She says her own research birds have never had any trouble orienting properly, though she runs her experiments in downtown Frankfurt.

But Richard Holland of Queen’s University Belfast in Northern Ireland said the results could “have quite significant implication for the behavior of migratory birds,” especially the hundreds or thousands of species that travel at night, when they can’t use cues from the sun.

Electromagnetic noise “is something we hadn’t considered,” he said. “I will openly admit that in my case, I didn’t really think that was an issue. But looking at this paper, birds are having to deal with it.”

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