Sensing Longitude Among Birds

Having the ability to tell direction with little or no obvious clues is a skill that would keep many of us from getting turned around or lost, even in our own towns. If we had the ability to find north no matter where in the world we were, we would spend a lot less time lost in the wrong neighborhood! We rely on GPS, maps, and other tell-tale signs to keep us on the right track- but how do other animals keep themselves in the right place?

Migratory animals have long fascinated scientists and researchers seeking to know how they know where to go. Salmon are able to find their way back to the stream they were born in; whales are able to make journeys of thousands of miles to Hawaii and back; and birds can find their way north and south when the seasons change. Each of these different animals have various ways they are able to determine direction.

Birds are one animal that are able to sense magnetic fields. They are able to distinguish between magnetic north and true north, a distinction that is very important when they are migrating. True north and magnetic north are different because of the shifting of the Earth’s axis as it turns. Birds are able to pinpoint magnetic north and determine their longitude with that information.

When birds migrate, they can use their ability to sense the difference between magnetic and geographic north to know where they are on the east-west spectrum as well.

Eurasian reed warblers have been of special interest to researchers. These birds migrate in the autumn season from Europe to sub-Saharan Africa. The researchers used birds that were used to making this regular migration in their study. In the study, researchers changed the magnetic field of the birds’ enclosures to mimic that of the magnetic field that exists in Scotland. The birds changed their position from their original direction, facing southwest, to the southeast, which would be the direction they would have to fly in that changed magnetic field.

Figure from Migratory Eurasian Reed Warblers Can Use Magnetic Declination to Solve the Longitude Problem, Chernetsov et. Al, 2017.

Figure from Migratory Eurasian Reed Warblers Can Use Magnetic Declination to Solve the Longitude Problem, Chernetsov et. Al, 2017.

Rather than using directional tools like stars to choose their path, this study showed that the Eurasian reed warbler is able to sense magnetic declination and use that information to determine their migratory flight path. As the stars in the sky remain in a fixed position pointing to geographic north, birds would have to be able to sense magnetic north in order to find their position longitudinally.

This ability to sense magnetic declination, or the difference between geographic (‘true’) north and magnetic north, is essential for the migration of many species of birds. Without this ability, they would not be able to find their way to their southern migration environment or back home to the north when it was time to move again.

By studying the migration habits of birds, researchers can work on understanding how these unique creatures are able to find their way through the air across thousands of miles and back again, all based on the time of year.

The study:


Chernetsov, N., Pakhomov, A., Kobylkov, D., Kishkinev, D., Holland, R. A., & Mouritsen, H. (2017). Migratory Eurasian reed warblers can use magnetic declination to solve the longitude problem. Current Biology, 27(17), 2647-2651.

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