The arctic tern is a water-loving bird that hatches during summer in the Arctic Circle, the northernmost part of the Northern Hemisphere. During the unbearably cold, dark arctic winter, the arctic tern flies south, following the summer season all the way to the Antarctic Circle on the other side of the Earth.
Because arctic terns do not fly in a straight line, the distance they fly every year is even longer than the approximately 30,000-kilometer (18,641-mile) from Arctic Circle to Antarctic Circle. This makes the arctic tern’s migration one of the longest of any animal on Earth.
Like a lot of other birds, arctic terns eat fish. They catch fish by gliding over the ocean, then plunging their feet or beaks in the water to skim fish near the surface. Unlike pelicans or ducks, arctic terns are not good swimmers and don’t spend a lot of time in the water. Rarely, arctic terns will snatch flies or other insects out of the air, but they prefer fish and other marine creatures, such as shrimp.
Arctic terns have beaks that are almost the same shade of tomato-red as their webbed feet. They have gray-white bodies and a head of jet-black feathers, which looks almost like a baseball cap.
Arctic terns, which mate for life, can live to be more than 30 years old. This is a very long lifespan for such a small bird with such an extreme lifestyle.
A group of arctic terns is called a colony. A tern colony migrates together. Just as migration is about to take place, the normally noisy colony will fall silent. This behavior is called dread. After dread, the colony will take to the air and leave their home nests all at once.
It might be easy to scoff at how normal the arctic tern might seem. Their diet, appearance, and behavior are similar to other marine birds. But their extraordinary yearly wandering puts them in their own category in the bird world.
Arctic terns migrate to follow the summer sun. Seasons happen because Earth is tilted on its axis while it revolves around the sun. During winter, the Northern Hemisphere is tilted away from the sun’s warming rays. This is why it’s colder during the winter in places north of the Equator, like the United States.
When it’s winter in the Northern Hemisphere, the Southern Hemisphere is tilted toward the sun, experiencing summer. In December, when people in the United States are putting on sweaters and jackets, people in Argentina are getting out their sunscreen.
Polar regions experience less noticeable temperature changes than other parts of the globe. However, these regions experience a great difference in the amount of daylight hours. During summer, the Arctic and the Antarctic get almost 24 hours of sunlight. During winter, it is almost entirely dark.
The arctic tern, going from Arctic summer to Antarctic summer, may experience more daylight than any other animal. Terns migrate in search of summer sunlight. Sunlight illuminates the ground and the ocean surface, so the birds can see fish or insects more clearly. Summer weather is also usually calmer at sea, allowing the birds to fly more easily.
“It’s really difficult to migrate this far, for this long. But it’s even tougher to find food in the Arctic winter,” says Doug Inkley, senior scientist with the National Wildlife Federation.
"It’s a strategy for survival," said Inkley.
Of constantly pursuing summer, Greg Butcher of the National Audubon Society says, "If it weren’t so hard to do, everyone would do it.”
Evolving to Migrate
Over millions of years, arctic terns evolved to undertake their unique migration.
"They didn’t just get up one day and say, ‘Gee, I think I’ll fly to Antarctica,’" says Inkley.
Arctic terns are made for migration. They prefer to glide in the air for most of the year. They are so lightweight, they let ocean breezes carry them great distances without having to use a lot of energy flapping their wings. Arctic terns can sleep and eat, all while gliding. In fact, arctic terns are one of the few birds, besides hummingbirds, that can hover in midair.
"They could fly 1,000 miles a day if they didn't need to fuel up in between," Butcher said.
After fitting the birds with trackers, scientists learned that arctic terns fly thousands of miles out of their way to take advantage of the best weather and get the best food. They can bounce around every continent instead of flying in a straight line back home. Although most arctic terns return to their home nesting grounds, some birds veer off course. Arctic terns from Siberia have shown up in South Africa, while terns that hatched in Greenland have been sighted in Australia.
The whole journey only takes the terns a couple of months.
Other birds have pretty long migrations, including the barn swallow and the sooty shearwater. The sooty shearwater, in fact, goes almost as far as the arctic tern. Still, no other animal makes a commute like this.
You might think that such a small bird would get snapped up by predators, but that’s not the case. Arctic terns are not endangered, Butcher said. Their breeding grounds are in the high Arctic: the coldest, most remote part of the region. This makes their nests hard to find. Even arctic foxes, the birds’ main predator, have trouble finding them, Butcher said.
For the Birds
Join a birding association near you. The American Birding Association provides links to clubs in all American states and Canadian provinces.
Sometimes people migrate, too. The 1966 film The Endless Summer documents two surfers travelling around the world, following the summer season in search of the perfect wave.
During the nineteenth century, millions of arctic terns were hunted in North America and Europe. Their black and grey feathers were used to decorate women's hats.
favor or benefit.
American Birding Association
nonprofit organization focused on bird-watching (birding).
region at Earth's extreme south, encompassed by the Antarctic Circle.
line of latitude at 66.5 degrees south that encircles the continent of Antarctica.
the way something looks.
paralell of latitude that runs 66.5 degrees north of the Equator.
mammal native to the tundra and other Arctic climates.
small bird that migrates from the Arctic to the Antarctic.
alliance of countries that opposed the Allies during World War II. The Axis was led by Germany, Italy, and Japan.
small bird that often nests in barns and caves.
hard, protruding jaws of a bird.
anything an organism does involving action or response to stimulation.
to move from one place to another in a seemingly haphazard manner.
place where animals mate, give birth, and sometimes raise young.
light wind or air current.
grouping or classification.
group of one species of organism living close together.
to travel to and from specific places on a regular basis, usually for a specific purpose, such as employment.
management of a natural resource to prevent exploitation, destruction, or neglect.
one of the seven main land masses on Earth.
foods eaten by a specific group of people or other organisms.
bird behavior where a colony becomes silent and takes flight all at once. Also called a panic.
to put at risk.
to develop new characteristics based on adaptation and natural selection.
one of the light structures that cover the body of birds, often helping them to fly or keep warm.
small winged insect.
to take on energy that will be used later, usually over a long period of time.
to move smoothly and seemingly without effort.
to emerge from an egg.
northern, most isolated part of the North Pole region.
to stay still in the air while flying.
type of very small bird.
to shine light on.
type of animal that breathes air and has a body divided into three segments, with six legs and usually wings.
type of coal, often polished and used in jewelry. Also called lignite.
voyage or trip.
having to do with the ocean.
to reproduce or breed.
to move from one place or activity to another.
movement of a group of people or animals from one place to another.
National Audubon Society
conservation organization with a special focus on birds.
National Wildlife Federation
organization focusing on conservation education.
protected area built by birds to hatch their eggs and raise their young.
half of the Earth between the North Pole and the Equator.
able to be seen or attract attention.
large marine bird with a big bill.
to enter suddenly, especially into water.
animal that hunts other animals for food.
to orbit or spin around something.
person who studies a specific type of knowledge using the scientific method.
to laugh at or mock.
large part of the ocean enclosed or partly enclosed by land.
period of the year distinguished by special climatic conditions.
animal that lives near the bottom of oceans and lakes.
region of land stretching across Russia from the Ural Mountains to the Pacific Ocean.
alike or resembling.
to lightly touch or contact the surface of a substance.
to take or grab quickly.
precipitation made of ice crystals.
marine bird with a dark body and silvery underwing.
half of the Earth between the South Pole and the Equator.
time of year when part of the Earth receives the most daylight: The months of June, July, and August in the Northern Hemisphere and the months of December, January, and February in the Southern Hemisphere.
degree of hotness or coldness measured by a thermometer with a numerical scale.
device, usually attached to an animal, that follows its movements.
to lean or change direction.
to roam or travel without a specific destination.
state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.
connected by a thin layer of skin or membrane.
feathered limbs on birds, usually specialized for flight.
time of year when part of the Earth receives the least daylight: December, January, and February in the Northern Hemisphere and June, July, and August in the Southern Hemisphere.