Wavelength interference from electronics and AM radio stations disrupt the internal magnetic compasses of European migratory birds, explains a report published yesterday in Nature.
Seven years of double-blind experiments (new researchers replicating old experiments) led the report's co-author, Henrik Mouritsen, of the University of Oldenburg, Germany, to conclude that cities disrupt migratory bird patterns.
The Earth's magnetic field, virtually mapped for the first time earlier this week, clues in European robins to their migratory direction, the report details. But when electromagnetic waves from our devices pollute the atmosphere, the birds don't know which way to fly.
Mouritsen covered wooden huts housing his robins with aluminum plating (the traditional method of blinding birds from magnetic clues such as the sun or stars, Nature writes). When his team grounded the plating—reducing the electromagnetic interference on campus from 50 kilohertz to five megahertz—they found that the birds could orient themselves. Ungrounded, however, the frequencies were so strong that the bird could not find their way.
Until Mouritsen moved his experiment from a rural field site into the college town, there was very little evidence of humans' electromagnetic radiation affecting birds' migratory patterns.
He poses this question 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?"