Arctic Terns Never Fly the Road Less Taken

The Arctic tern is known for its record-breaking long migration. Every year these small birds migrate from the Arctic to the Antarctic—a daunting round-trip of about 50,000 miles (80,000 kilometers).

But terns don’t get bored and mix it up on their routes. New research finds that these slender, far-flying birds use just a few select routes for their travels.

“The Arctic tern’s migration is noteworthy because it holds the world record for the longest migration of any animal, and therefore interacts with a variety of ecosystems along the way,” lead author Joanna Wong, a graduate of the Institute for the Oceans and Fisheries (IOF) master’s program at the University of British Columbia, tells Treehugger.

The small seabird breeds in the Arctic and spreads the rest of its nonbreeding time in the Antarctic.

“I find that particularly impressive because they make this grand journey (and back) every year, and they have been known to live up to 30 years so they are really covering quite a remarkable distance throughout their lives (especially relative to their small size!),” Wong says.  

The population of Arctic terns is decreasing, reports the International Union for Conservation of Nature (IUCN). They’re threatened by predators such as mink, as well as the loss of habitat and key prey due to temperature changes.

“We don’t have a more far-ranging animal. They are an indicator species that can tell us so much about the different ecosystems that they travel through,” Wong says. “If they don’t make it to their destination in one year, then you know there might be an environmental problem somewhere along their route.” 

Because they have such a wide geographic range, however, it’s challenging for researchers to study tern colonies, specifically where they hit bottlenecks on their migratory routes.

“These birds are difficult to study because they are either residing in polar environments, or on the go, which are both difficult for humans to access,” Wong says.

The birds have been tracked in Europe, but no research has been done on Arctic terns in Canada, she points out, even though Canada is a key breeding location for the birds.

Mapping Routes

Most of the year, Arctic terns are away from their breeding colony so in order to track them, researchers need a device that is small, yet large enough to record information year-round.

For their study, Wong and her colleagues attached light-level geolocators to the legs of 53 Arctic terns from five breeding colonies across a wide range throughout North America. These geolocators are miniaturized computers that record ambient light intensities.

“The length of daylight can tell us the latitude, while the time of solar noon can tell us the longitude, so we are able to estimate positions of birds,” Wong says. “Luckily, because the birds return to the same breeding colony and nest each year, we can recapture the birds at the same location tags were deployed to retrieve the information from the tags.” 

Researchers compared the routes taken by the birds they followed in their study and the migration timing to other Arctic terns that had previously been tracked from Greenland, Iceland, the Netherlands, Sweden, Norway, Maine, and Alaska.

The results were published in the journal Marine Ecology Progress Series.

They determined that most Arctic terns that have been tracked globally use common migratory routes. So terns breeding in different areas such as Canada, the United States, Norway, and Greenland, all end up taking similar routes both when they head south and then again when they return north, Wong says. Their chosen paths are likely influenced by wind and the availability of food, she says.

They found that the majority of Arctic terns used one of three routes when journeying southbound—Atlantic West Africa, Atlantic Brazil, or Pacific coastal. Most birds took one of two northbound migration routes: mid-ocean Atlantic or mid-ocean Pacific.

Some other seabirds also use these same paths, which suggests that the routes aren’t specific just to the Arctic terns, Wong says, and that protecting them may be beneficial to other species.

They also found that migration for the birds generally fell within a 1-2-month window.

“These results are important because it suggests that conservation management of Arctic terns could be dynamically adapted to the spaces and times of the year that terns are using certain portions of their route, such as through mobile marine protected areas, which would make the conservation of such a far-ranging animal more feasible,” Wong says.