The most migratory bird is the Arctic tern. The Arctic tern travels farther than any other bird species in its annual migration from its Arctic breeding grounds to Antarctica and back again. This incredible round-trip journey covers over 70,000 km (44,000 miles) each year!
Why does the Arctic tern migrate so far?
The Arctic tern migrates such extreme distances because of its specialized breeding habitat needs and the extreme seasonal conditions of its breeding and wintering grounds. The Arctic tern nests in the high Arctic during the northern summer, when conditions allow for abundant food and 24 hours of daylight for successful breeding. However, the winter darkness and freezing conditions make the Arctic uninhabitable. The birds must migrate south to find food and more favorable conditions. Their winter home in Antarctica provides round-the-clock sunlight and plentiful ocean food sources. However, Antarctica lacks the bare ground and insect food sources needed for breeding in summer. So the long migration allows the Arctic tern to take advantage of the best of both polar regions.
Arctic Tern Migration Route
The Arctic tern’s migration route spans multiple continents. From their Arctic breeding grounds, the birds fan out across Canada and the northern Atlantic Ocean to staging areas in western Europe and the west coast of Africa. Then they proceed south along the coast of Africa to Antarctica for the southern summer and winter. In spring, they return north, following a similar but slightly more eastern route. Their circuitous path takes advantage of global wind patterns that provide beneficial tailwinds during both legs of the journey.
Fall Migration
The Arctic tern’s southbound migration in the northern fall follows this general route:
- Depart Arctic nesting grounds in northeast Canada, Alaska, Russia and Scandinavia
- Stage in the waters off Greenland, Iceland, and Western Europe
- Fly down the west coast of Africa
- Arrive in Antarctica by December
Spring Migration
The northbound return trip in spring follows a slightly more eastern route:
- Depart Antarctica by mid-March
- Stage along the northwestern and western coasts of Africa
- Fly up the east coast of North America
- Arrive in the Arctic by mid-May to breed
This elliptical path takes advantage of circular global wind patterns and provides the most efficient routing with beneficial tailwinds.
Incredible Duration and Distance
The Arctic tern’s annual round-trip spans over 70,000 km (44,000 miles) from pole to pole. That is the longest migration of any bird species. For comparison, the marathon migratory journeys completed by birds like the frigatebird, sooty shearwater, and bar-tailed godwit clock in between 20,000-30,000 km.
The Arctic tern’s migration is so long, a bird hatched this year will not return to the place where it was born until its 4th year of life! Over a lifetime of 30 years, a single Arctic tern may fly over 2.4 million km (1.5 million miles). That is equivalent to 3 round trips to the Moon!
This extreme odyssey requires high flight efficiency. Arctic terns fly smoothly to conserve energy, angling their slender wings to catch beneficial winds. Their long, forked tail streamlines the body and provides control and stability in flight. With no wasted wingbeats, these champion fliers achieve airspeeds over 110 km/h (70 mph).
Breeding in the Arctic Summer
Arctic terns arrive back in the high Arctic by mid-May, ready for the brief but busy summer breeding season. The nonstop daylight, abundant insect food, and snow-free ground provide ideal conditions for raising chicks.
Both the male and female Arctic tern defend nesting territories. The birds nest in scrape nests on the bare ground of coasts, islands, and wetlands. Nesting in colonies provides some safety in numbers from predators like foxes, gulls, ravens, bears, and polar bears.
The female lays 1 – 3speckled olive or brown eggs, and both parents share incubation duties. The eggs hatch in about 3 weeks. The chicks are fed regurgitated fish by both parents and fledge in 3 – 4 weeks, one of the shortest fledging times of any bird. This rapid chick development makes the most of the brief Arctic summer season. The young Arctic terns depart on their first southern migration in late August or early September.
Wintering in Antarctica
By November, the entire Arctic tern population has traveled to Antarctica and the surrounding Southern Ocean waters. Here they find plentiful marine food as well as the endless daylight needed for foraging in the austral summer.
The birds feed primarily on fish, squid, krill and other small marine animals. Skimming low over the water, their sharp eyes spot prey silhouetted against the bright polar waters. Plunging headfirst into the sea, they snap up food in their thin pointed bill before any prey can react and escape.
The Antarctic waters stay free of pack ice even through the winter months, providing vital open areas for the terns to remain at their wintering grounds year round. Here they undergone their annual molt, replace all their feathers in preparation for another long migration and breeding season. Come mid-March, the urge to migrate northwards returns, driven by the season’s shift in daylight length.
Navigational Abilities
The Arctic tern’s extreme pole-to-pole odyssey demonstrates an incredible ability to navigate across thousands of miles over featureless oceans. Scientists are still studying how they accomplish these marathon intercontinental migrations.
Several theories exist on how the birds find their way:
- Using the sun’s position as a compass reference during the day.
- Navigating by the stars’ positions on clear nights.
- Detecting the earth’s magnetic field through an internal compass sense.
- Using their keen sense of smell to follow a succession of odor cues along the migration route.
In reality, Arctic terns likely use a combination of these navigational tools, along with following coastlines and continental shelves when possible. Their ability to return to the exact same breeding and wintering sites year after year remains one of the great wonders and mysteries of the natural world. This navigational programming is so precise, a young bird completing its first unassisted migration can find its way alone to the traditional winter quarters it has never seen before.
Threats and Conservation
The global population of Arctic terns is estimated at around 2 – 3 million pairs. Overall numbers are believed stable, though some regional declines have been noted in areas like the Netherlands.
Threats to Arctic terns include:
- Disturbance, predation and habitat loss at breeding colonies
- Overfishing of food sources at migratory stopovers
- Oil spills and marine pollution throughout migration route and in Antarctica
- Climate change impacts on nesting and feeding habitats
Tracking studies by geolocator have greatly increased knowledge of the Arctic tern’s migratory habits and key sites. This allows better targeted conservation efforts along their flyway.
In the Arctic breeding grounds, managing predators, limiting human disturbance near colonies, and protecting crucial coastal nesting habitats can benefit Arctic terns. International cooperation is needed to monitor and reduce threats in Antarctica and along the migration pathway. Given suitable conditions, this incredible global traveler will continue its pole-to-pole marathon into the future.
Conclusion
The Arctic tern is a true champion of the animal kingdom, completing the longest yearly migration of any bird species. Its extreme journey spans over 70,000 km round-trip from the high Arctic to Antarctica and back. This pole-to-pole odyssey demonstrates the Arctic tern’s amazing adaptations for extreme long-distance flight and its incredible navigational abilities guiding it across oceans and continents. While threats exist, focused conservation efforts centered on protecting key breeding habitats and migration sites can help ensure the survival of this marathon migratory bird into the future. The Arctic tern’s epic global journey remains one of the great natural wonders of the world.