The Arctic Tern, the Bird that Migrates the Farthest

Oct 11, 2010
Bob Bowers

The Arctic Tern, Sterna paradisaea - Bob Bowers

Many animals, from Monarch butterflies to Gray whales migrate thousands of miles twice annually. The most impressive feat of all is that of the Arctic Tern.

Although animal migration has been studied extensively, much remains to be understood. For birds, migration in some cases is just a short day trip, while for others it means a perilous long-distance adventure. Of all migrating animals, none can match the semi-annual 11,000 mile journey of the Arctic Tern.

Migration of Animals and Birds

There is no shortage of amazing migration stories about birds and animals. Gray whales leave their arctic feeding grounds each fall, and swim some 5,000 miles to the shallow nursery lagoons on the west coast of Baja California, the longest migration of any mammal. Considering their lightweight fragility, Monarch butterflies accomplish an even more daunting task, flying up to 2,000 miles from North America to their wintering grounds in the high Oyamel firs of central Mexico. The Monarch migration is all the more impressive, since it only takes place every fifth generation.

While many bird species are year-round residents, not migrating at all, others migrate twice annually, between their winter homes and their summer breeding grounds. For some birds, this involves nothing more than a short trip, such as moving to a lower elevation. Many birds, on the other hand, take on monumental and life-threatening trips, far across open ocean or over great distances. Many of these migrations are near-miraculous, such as that of the Red Knot, where the adults depart their arctic breeding grounds two weeks before the young, yet the fledglings somehow find their way 9,000 miles to rejoin their parents in Tierra del Fuego.

It is generally believed that migrating birds more likely evolved as tropical birds seeking more productive breeding grounds, rather than temperate birds seeking winter havens. The longer summer days of the temperate latitudes, coupled with exploding insect populations and more nesting opportunities, provide strong motivation for birds to undertake the risk of migration. In any case, the rewards must be significant, because they come at an enormous cost. Long-distance migration subjects birds to exposure, fatigue and predation, and less than half of southbound birds from the U.S. and Canada return north the following spring.

The Arctic Tern (Sterna paradisaea)

The Arctic Tern (Sterna paradisaea), at 12 inches in length, and with a wingspan of 31 inches, is similar in size to the Forster's Tern and the Common Tern, two other medium-sized terns with which the Arctic shares similar habits, voice and plumage. The Arctic Tern is primarily a pelagic bird, spending its non-nesting time at sea. During its breeding months (March-October), however, it can be seen on shorelines and in marshes from Alaska, across Canada to the northeastern U.S. coast, at places such as Machias Seal Island off the coast of Maine.

Arctic Terns are monogamous, producing one brood annually of 1-3 eggs. Incubation requires about three weeks, and the semi-precocial birds fledge in three to four weeks. Their diet consists primarily of insects, crustaceans and aquatic invertebrates. Courtship is conspicuous and elaborate, both on ground and in the air, and males bring small fish and feed their mates during courtship.

Arctic Terns are colonial, and can be found during the nesting season together with Common and Aleutian Tens, Atlantic Puffins and Razorbills. As is the case with many other pelagic birds, they also are long-lived, with one recorded lifespan of 34 years.

The World Champion Migratory Bird, the Arctic Tern

Arctic Terns nest in the northernmost reaches of the Arctic, as far as latitude 84 degrees, and winter as far south as Antarctica, where they have been recorded at latitude 78 degrees. Typically, their migration route is 11,000-12,000 miles, although for some birds it has been noted at more than 15,000 miles, equalling an annual round trip journey as high as 31,000 miles, roughly equivalent to a flight around the world. Considering the bird's prolonged lifespan, this annual feat translates to a lifetime migratory flight of more than a half-million miles.

Newly-fledged Arctic Terns, however, get a break from this monumental migration. Once they have left their nest and make the long journey south, they skip the first spring return, since they, like other terns, do not breed that first year.

The Arctic Tern's Place Among Animal Migration

It would be subjective and difficult to select the most challenging of all animal migrations. The Gray whale's 10,000-mile round trip swim is an impressive contender, as is the miraculous multi-generational migration of the Monarch butterflies of North America. Amazing bird migrations are numerous, including the open ocean crossing by Ruby-throated Hummingbirds, and the 9,000-mile flight of newly-fledged Red Knots, unaccompanied by their parents. For sheer mileage, though, no bird or other animal can equal the feat of the Arctic Tern, the long-distance champion.

For more information about migrations and other birds seen with the Arctic Tern, see the following:

References:

Elphick, Chris, Dunning, Jr., John B. and Sibley, David Allen (2001), The Sibley Guide to Bird Life & Behavior, Alfred A. Knopf, ISBN 0679451234