Next time you're listening to the radio, give a thought to migrating birds. New research has shown that radio signals might be confusing their built-in natural compass.

A study in Germany has proven that electronic "noise" generated by humans with their ubiquitous devices can affect birds' navigation system, which depends on their ability to accurately sense the Earth's magnetic field.

Birds could have problems attempting to fly through a busy human-created electromagnetic environment with potential disruptions at multiple wavelengths, says neuroscience Professor Henrik Mouritsen of the University of Oldenberg.

"Basically, anything you plug into a plug will send out electromagnetic noise at some frequency," he says.

While birds can also navigate using the stars and the sun, when flying in overcast weather in an urban area pumping out electromagnet noise, a bird could have a difficult time, he says.

"If it doesn't have any compass available, it might not migrate at all... or it might fly in a random direction," he says. "We don't really know."

A worrying decline in populations of migratory songbirds, long noticed by scientists, could be at least partly explained by the effect of human-generated electromagnetic fields is having on the biological processes by which birds successfully navigate to their ultimate migratory destination, the researchers say.

The exact sources of the interfering fields aren't known, they say, although they've ruled out power lines and cell phones because their frequencies are too high or too low. Still, devices from AM radios to computers, refrigerators, microwave ovens or even lights can create electromagnetic fields.

Mouritsen has dubbed the many electromagnetic fields such devices can emit "electrosmog."

And it doesn't take much, the researchers report in the journal Nature. Fields weaker than anything that could possible harm humans -- a thousand times weaker than health limits the World Health Organization has set -- can seriously cripple a bird's magnetic navigation system, they said.

Mouritsen acknowledges it would be unrealistic to expect humans to just "unplug" from technology for the birds' sake, but suggests small steps -- like keeping strong AM radio transmitters away from known bird migratory routes -- could help.

"I'm pretty sure the birds would be better off if their magnetic compasses were not disturbed," he says.

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