For years now, scientists have said certain animals have the ability to sense the Earth's magnetic lines of force and use them to navigate during migration.
Until now, though, there was little proof of what it took to pull this feat off.
Researchers at Sweden's Lund University have identified a single protein that birds use to orient themselves to the Earth's magnetic field.
The scientists believe the proteins are located in the birds' eyes. Using zebra finches, they discovered a protein called Cry4 in their eyes that maintains a constant volume throughout the day and even in varying light conditions.
The abbreviation for the name of the protein comes from the class of proteins it belongs to, known as cryptochromes, a class of flavoproteins. Cryptochromes are sensitive to blue light and, interestingly, are found in plants and animals where they are known to be involved with circadian rhythms - or the cycles of light and dark. In plants, they are thought to trigger parts of the organism's development.
It makes sense, then, that small genetic mutations throughout time might result in a cryptochrome that is sensitive to magnetic fields and thus provide an advantage to those individuals who inherited it.
"Cry4 is an ideal magnetoreceptor, as the level of the protein in the eyes is constant. This is something we expect from a receptor that is used regardless of the time of day," explained Atticus Pinzón-Rodríguez, one of the researchers behind the study. His interview appeared in Science Daily this week.
So, do these birds actually "see" magnetic fields? The answer right now is perhaps. Similar magnetoreceptive compounds are speculated to exist in other animals as well.
It's one thing to have a compass. But it's another to be able to navigate with amazing accuracy as many animals do following the same flight paths and finding the exact same square meter of ground or water months later.
Visually, landscapes change, too. A fallow field a square mile in size looks far different after a farmer plants the next season. And a river is different once man diverts flows and constructs massive dams.
Anyone who has studied navigation knows, too, that magnetic compasses can be remarkably inaccurate. This is due in part to the fact that the Earth's magnetic fields are not as uniform as many imagine.
Last year, a very large weak spot known as the South Atlantic Anomaly was discovered, covering much of South America, the south Atlantic and the southern tip of Africa. This weakness allows things like cosmic rays and charged particles to reach far lower in our atmosphere than in places where the field is stronger.
Local magnetic fields cause compasses to deviate, too. Every compass is supposed to point to true north, but they point to magnetic north and must be corrected. Magnetic declination is the difference between magnetic north and true north. Magnetic deviation is the difference between true north and local sources of magnetic interference, such as the iron in a massive ship sporting a compass at the helm. These have to be accounted for.
"How do animals do this?" asked the column writer as he shrugged his shoulders.
The reason to bring all this up is not to make magnetic navigators out of readers, but to impress upon us the concept that we still have a lot to learn about animal navigation.
Imagine, however, if one could visualize, even faintly, the magnetic lines of force surrounding us. Might it be valuable, or might it be like so many scribbles in our vision thanks to all our electronics?
Animals make it seem easy.
Charlie Powell is the public information officer for the Washington State University College of Veterinary Medicine, which provides this column as a community service. For questions or concerns about animals you'd like to read about, email cpowell@vetmed.wsu.edu.
