From turtles to albatrosses, many species migrate long distances, normally in a quest for food or mates. But exactly how these animals manage to stay on track while traversing thousands of kilometers across land and sea has managed to evade scientists and remained a mystery. A new study has, however, been able to show that manipulating the magnetic field to which a migrating bird is exposed correspondingly alters its direction of travel.
“If you just change the magnetic field, you can give them information about their position,” Dmitry Kishkinev, who coauthored the study published in Current Biology, explained to IFLScience. “And this is important because people believe that it’s very well-known and that experiments show that birds use magnetic fields, but it’s not. Until now, we had some correlated evidence, but no direct evidence.”
Previous research has shown that migrating song birds transported across entire continents can still manage to readjust and fly in the direction of their end destination. There is also strong evidence to suggest that some birds, such as homing pigeons and seabirds, will use their sense of smell to guide them to the right location. But so far surprisingly little is known about the use of magnetic maps in migrating birds.
In earlier research, Kishkinev and his team showed that when migrating Eurasian reed warblers were captured near the Baltic Sea and flown 1,000 kilometers (620 miles) east to Zvenigorod near Moscow, they were able to compensate for this new position. Rather than continuing to fly northeast as they would on their normal migratory route had they not been moved, they started to fly northwest, toward their original destination. As the birds fly at night, in the absence of visual cues, they suspected that they birds could be using magnetic fields to orient themselves, and decided to try and test this idea.
The "magnetic contraption" built by Kishkinev and his team managed to trick the migrating song birds. Dominik Heyers/University Belfast
“We basically didn’t transport the birds this time, but we kept them here in the [Baltic] region, inside this special equipment to manipulate the magnetic field,” explained Kishkinev. “It’s a magnetic coil system. It’s like a cage basically, and inside this cage you can manipulate the magnetic field. During the week they were in the cage, they were magnetically displaced to the Moscow region, so the behavor was very similar to the ones which were geographically displaced.”
When in the cage, which was open to the elements to allow the birds to see the landscape and stars at night, the researchers found the birds did not align northeast, as would be expected by normal migrating warblers. Instead, they tried to fly northwest, as if they had been moved to Zvenigorod. When released, the birds continued to follow this bearing and flew in the wrong direction, showing how changes exclusively in magnetic information could alter the bird’s movements.
While they weren’t able to show that after release the birds could then get back on the correct migratory route, Kishkinev suspects that the birds are able to readjust their magnetic map every night, to make sure they keep on track while traveling long distances.
What still remains unknown, however, is how exactly the birds are tracking these changes in their brain. Kishkinev’s best guess so far is that magnetic information is passed to the brain via the ophthalmic nerve, as previous research has shown how damage to this nerve can prevent warblers from reorienting themselves when displaced.
Main image credit: Andy Morffew