How a Tern Broke the Record for the Longest Known Migration

Researchers call the bird’s journey of 60,000 miles an “underestimate” of how far it actually flew.

This month in Britain, an unassuming little bird broke a huge record. An Arctic Tern clocked a whopping 59,650 miles over the course of its yearly migration from its breeding area on an island off the coast of England to Antarctica, and then back again. The tern’s trip marks the longest migration ever recorded—the equivalent of flying around the circumference of the Earth twice, plus 10,000 miles.

Leaving the Farnes Islands last July, the tern reached the tip of South Africa in just one month. From there it flew to the Indian Ocean, where it stayed throughout October until departing for Antarctica. The tern then angled along the edge of the continent and, in early March, arrived in the Weddell Sea, which became its home until April, when it flew back to the Farnes along the west coast of Africa. The epic round-trip journey is nothing short of inspirational.

“We know that terns are moving and flying constantly, even at night. And we know that flying is the most energetic activity that any animal can undertake,” said Richard Bevan, a biologist at Newcastle University and one of the study’s lead scientists. “How do they do it? We don’t yet know, but it is extraordinary.” With a record like this already underway, this particular tern may fly more than 1,800,000 miles over the course of a lifetime that could span up to 30 years—the equivalent of traveling to the moon and back four times.

Racking Up the Miles

The study has illuminated the monumental scope of one of the best-traveled creatures in the world. Bevan and Newcastle’s Chris Redfern have been studying the birds of Farnes Island for almost 20 years. Approximately 3,200 Arctic Terns breed there, a population that blooms when eggs hatch in June. Then the tern chicks must share cramped island real estate with thousands of hatchlings from some of the island’s 87,000 pairs of seabirds, including the Arctic Terns, Atlantic Puffins, Common Eiders, and Sandwich Terns.

Last year the researchers fitted 29 of the Arctic Terns with geolocators, tiny gadgets weighing 0.7 grams that monitor light levels from bands on the birds’ legs. The geolocators record the maximum light level every five minutes, from which researchers can determine the times of sunrise and sunset, the day length, and ultimately the bird’s precise location.

The record-breaking bird—which the researchers believe to be female due to its wingspan and the length of its body and tail—is only seven years old. Bevan remembers tagging it as a chick in almost the exact spot where the bird now nests.

The Arctic Tern’s extreme flying is rivaled only by the Bar-Tailed Godwit, a truffle-feathered shorebird that has set the record for the longest nonstop flight (not even a brief rest for a drink or food): 7,145 miles in the air. But nothing in the entire animal kingdom beats the Arctic Tern’s track record for distance. This bird’s near 60,000 miles tops the previous record of 56,544 miles. But Bevan says he won’t be surprised if it’s soon surpassed by another bird’s flight because tracking technology is constantly expanding scientists’ understanding of the animals’ miraculous feats. So far this year the researchers have recovered 17 of the geolocators from tracked birds, and have sighted another four or five that they hope to catch in the coming weeks, so that new record could come rather soon.

Because they only record the daily positions of the birds, geolocators will always underestimate the total distance the birds fly, Bevan says. GPS satellite transmitters would expand tracking capabilities tenfold, but the technology is currently too heavy for the small birds. “If we can get GPS devices small enough, I think we would see these birds have gone truly phenomenal distances.”

A Harrowing Lifestyle

The Arctic Terns’ circumpolar migration takes them to every ocean and near every continent. They travel in a seemingly inefficient zigzag of long loops and s-curves. But there is a method to this madness. Scientists recently discovered the birds make several thousand-mile detours to capitalize on global wind patterns and preserve energy. The sprawling migration represents a necessary hunt for resources, Bevan hypothesizes. After all, the terns rely on the Farne Island to breed and the Antarctic to eat. “Finding out where they’ve been going, looking at what resources are there is very important,” he says.  “The extent of the area that these birds are actually using down south is quite an eye-opener to us.”

These are the real implications of the study: zeroing in on the terns’ migration hotspots and what threatens them will immeasurably aid their conservation. “Identifying such areas that are going to be important not just for this one bird, but for a lot of the birds,” Bevan added. When it comes to conservation, the Arctic Tern’s migratory claim to fame also marks its biggest blind spot. With such an extensive range, populations are much more difficult to monitor. “We think of them as our birds, but they’re not,” Bevan says. “They spend most of their time elsewhere, going into five different oceans and sampling all sorts of environments.”

Though the global population of Arctic Terns is not yet threatened, researchers believe they are slipping into a soft decline. The bird’s numbers on the Farnes have also slumped, especially after a bout of harsh summer storms last year, events that are predicted to intensify with climate change.

Other colonies in Iceland and Scotland fare even worse, Bevan says. These northern flocks have resorted to traveling farther in pursuit of sand eels—the chosen cuisine of terns, puffins, and auks—which in turn have been drifting to the north to escape rising sea temperatures. It’s also possible that sand eels have drifted down into deeper and therefore colder waters, jeopardizing non-diving birds like the tern that can’t access prey below the surface.

Arctic Terns feed by plunge-diving, an exhausting method that involves flying 30 meters vertically up and down to catch fish at the surface of the water. The geolocators revealed that downtime means nothing to the terns, who are moving and flying constantly day and night. It’s an exhausting life, and researchers still aren’t sure how they find the energy to do it.

So the Arctic Tern’s sensitivity to such environmental shifts has earned it the moniker of “canary of the sea,” Bevan says. “If anything goes wrong, these birds are the first to be affected.” But this means the location data of the Terns could double as a marker of fish stocks and where they move in response to climate change.

Though Bevan and Redfern will not track their birds this coming year, they hope to secure enough funding to continue the project in the future. For now, they will thoroughly analyze the migration path of each bird and see where they overlap, hoping to identify conservation hotspots. “We’re at an early state of understanding, but this is an extraordinarily valuable data set that will tell us a lot about how these terns use our planet,” Redfern says. “And I think that’s remarkable.”

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