Arctic Tern: The World Record Holder of Long-Distance Migration
The Arctic tern (Sterna paradisaea) is a medium-sized seabird belonging to the family Laridae. Renowned for its extraordinary endurance, this species undertakes the longest migration of any known animal in the kingdom. By traveling between the Arctic and Antarctic regions, the Arctic tern effectively experiences two summers every year, granting it more daylight than any other creature on Earth.
Key Facts
- Migration Record: Some individuals have been tracked covering up to 96,000 km in a single ten-month period.
- Lifespan: Long-lived birds that typically reach 15 to 30 years, with a record of 31 years.
- Diet: Primarily carnivorous, feeding on small fish and marine invertebrates.
- Conservation Status: Listed as Least Concern by the IUCN, though some regional populations are vulnerable.
- Global Population: Estimated at over two million individuals.
Physical Characteristics and Identification
The Arctic tern is a sleek, medium-sized bird with a length of 33–36 cm and a wingspan ranging from 76–85 cm. Weighing approximately 100 g, it is built for efficiency with high aspect ratio wings and a deeply forked tail.
During the breeding season, the bird is characterized by a grey and white plumage, a black crown and nape, and a striking blood-red beak and feet. In winter, its appearance shifts slightly; the forehead becomes partly white, and the bill and legs turn black. Juveniles are distinguished by a partly white forehead and pale orangey-brown fringes on their grey mantle feathers.
Distinction from Similar Species
While it resembles the common and roseate terns, the Arctic tern can be identified by its longer tail and uniformly colored bill compared to the common tern. It also possesses longer wings and a darker hue than the roseate tern. Furthermore, its call is notably more nasal and rasping.
The Epic Journey: Distribution and Migration
The Arctic tern maintains a circumpolar breeding distribution, meaning it breeds across the Arctic and subarctic regions of North America, Europe (as far south as Brittany), and Asia (as far south as Massachusetts). When the northern summer ends, these birds migrate to the Antarctic coast to coincide with the southern summer.
While the shortest distance between these poles is roughly 19,000 km, Arctic terns do not fly in a straight line. They follow convoluted, meandering routes to take advantage of prevailing winds.
Recent tracking data has revealed the staggering scale of these journeys. Birds nesting in Iceland and Greenland average annual round trips of 70,900 km. A specific individual from the Farne Islands in Northumberland, tagged with a light level geolocator, set a global record by covering 96,000 km in just ten months. Over a typical 30-year lifespan, an Arctic tern may travel approximately 2.4 million km—the equivalent of three round trips from Earth to the Moon.
Ecology, Diet, and Reproduction
The Arctic tern is primarily a carnivore. Its diet consists mainly of small shoaling fish such as herring, cod, sandlances, and capelin. It also consumes marine crustaceans like krill, amphipods, and crabs, and occasionally eats molluscs, marine worms, berries, or insects.
To secure food, the tern dips to the water's surface or chases insects in the air. Interestingly, they may engage in kleptoparasitism—the act of stealing food from other birds—by startling conspecifics or other species like auks and grebes into releasing their catch.
Breeding and Life Cycle
Nests are typically simple depressions in the ground, sometimes lined with grass. Both parents share the responsibility of incubating the mottled, camouflaged eggs. The hatching process takes 22–27 days, and chicks fledge after 21–24 days. Because they invest significant time and energy into raising only a few offspring, they are classified as K-selected species.
Conservation and Cultural Impact
Currently, the Arctic tern is categorized as a species of Least Concern by the IUCN. However, they face regional challenges. In New England, populations were historically reduced by the millinery trade (hunting for hats), and in western Greenland, exploitation has reduced numbers since 1950. In Iceland, the species was uplisted to vulnerable in 2018 due to a crash in sand eel stocks.
The bird's legacy extends into culture and science. It has appeared on postage stamps in countries like Canada, Finland, and Iceland. Additionally, the European constellation of polar-orbiting weather satellites, EPS-Sterna, is named in honor of the bird's legendary migrations.
| Feature | Detail |
|---|---|
| Scientific Name | Sterna paradisaea |
| Average Annual Migration | 48,700 km to 70,900 km |
| Maximum Recorded Migration | 96,000 km (10 months) |
| Weight | 86–127 g |
| Primary Diet | Small fish and marine crustaceans |
| IUCN Status | Least Concern |
Frequently Asked Questions
How far does an Arctic tern travel in its lifetime?
Based on research, an average Arctic tern living 30 years will travel approximately 2.4 million km, which is more than three times the distance of a round trip from Earth to the Moon.
Why do Arctic terns take meandering routes during migration?
They follow convoluted paths rather than straight lines to take advantage of prevailing wind patterns, which helps them conserve energy during their long journey.
What is the difference between an Arctic tern and a common tern?
The Arctic tern generally has a longer tail, a uniformly colored bill, and a more nasal, rasping call compared to the common tern.
What are the main threats to the Arctic tern?
While the global population is stable, regional threats include historical hunting for the millinery trade and the depletion of primary food sources, such as the crash of sand eel stocks in Iceland.
What does it mean that Arctic terns are K-selected?
Being K-selected means they are long-lived birds that invest a significant amount of time and energy into raising a small number of offspring, rather than producing many offspring with low survival rates.