Scientists have known for decades that migratory birds use the Earth's magnetic field as a type of GPS system to orient themselves. Researchers, however, have been unsure how they do it.

The study by scientists from Arizona State University and the University of Oxford in Britain focused on a molecule that is sensitive to both the magnitude and the direction of a magnetic field that is one-twenty-thousandth as strong as a refrigerator magnet, ASU said in a news release. The report is published in the journal Nature.

ASU biochemist Devens Gust said the findings "provides the first proof that this mechanism can actually function with magnetic fields as small as those of the Earth." He said research has shown that both broadband radio noise and constant frequency signals disrupted magnetic orientation in European robins.

Gust said research does not prove birds actually use this mechanism, only that they could.