The Arctic tern (Sterna paradisaea) is a medium-sized seabird species that breeds in the Arctic and subarctic regions. The Arctic tern is well known for its incredibly long yearly migration, flying from its Arctic breeding grounds to the Antarctic region each year. This round-trip journey means the Arctic tern sees more daylight than any other animal on Earth! So what makes the Arctic tern so special and enables its record-breaking migrations?
Physical Characteristics
The Arctic tern has several physical adaptations that allow it to fly huge distances:
- Lightweight body – Terns have lightweight, narrow bodies to minimize energy usage in flight. The Arctic tern weighs just 90-120g.
- Long, pointed wings – Long, narrow wings enable terns to glide efficiently for long periods.
- Streamlined shape – Their aerodynamic body profile reduces drag.
- Forked tail – The forked tail provides stability and maneuverability in flight.
- Webbed feet – Webbed feet help terns swim and take off from the sea surface.
These adaptations give the Arctic tern energy-efficient flight and the ability to fly thousands of miles at sea without stopping.
Extreme Endurance
The Arctic tern undertakes the longest yearly migration of any bird species. Each year it flies from its Arctic breeding grounds to the Antarctic region and back again. This round trip can cover over 90,000 km – that’s more than twice the circumference of Earth!
Some key facts about the Arctic tern’s epic journey:
- Total distance – Up to 90,000 km round trip
- Duration – About 3 months in each direction
- Route – Primarily over oceans in S-shaped course
- Speed – Average 22 mph but up to 40 mph with tailwinds
- Non-stop flight – Over ocean with only short stops on land
The Arctic tern’s extreme endurance allows it to experience more daylight than any other animal. By always moving towards summer in the northern and southern hemispheres, the tern enjoys up to 20 hours of daylight per day!
Navigation
One question is how Arctic terns manage to navigate these huge migrations year after year. Researchers believe they use multiple cues:
- Sun compass – Terns use the sun’s position to determine direction.
- Star navigation – On cloudy nights, stars help terns orient themselves.
- Earth’s magnetic field – Terns can sense magnetic fields to judge latitude.
- Landscape memory – Terns remember key migration routes and landmarks.
- Polarized light – Light patterns near the horizon provide orientation clues.
By combining these navigation methods, Arctic terns can successfully migrate from the Arctic to Antarctica and back each year, even to the same breeding sites.
Breeding
Arctic terns nest in huge colonies in the high Arctic during the region’s short summer breeding season.
Key facts about Arctic tern breeding:
- Location – Arctic sites like coastal tundra and islands
- Nest – Small depression on bare ground
- Eggs – Usually 2 eggs per clutch
- Incubation – Around 3 weeks by both parents
- Fledging – 3-4 weeks after hatching
- Defense – Aggressively dive-bomb predators
Raising chicks during the brief Arctic summer requires both parents to work together and strategically time breeding. The chicks must grow quickly to be ready for the long southward migration.
Diet
The Arctic tern is carnivorous, feeding primarily on small fish, shrimp and invertebrates. Its diet includes:
- Small fish – Capelin, sand lance, Arctic cod
- Crustaceans – Krill, amphipods, small shrimp
- Invertebrates – Squid, marine worms, jellyfish
Terns hunt by plunge-diving for prey in oceans or estuaries. They can fish in shallow waters or dive up to 1-3 feet deep to catch prey. Their slender, pointed beak is an effective spear for snatching fish.
Arctic terns defend feeding territories both in breeding grounds and on migration. Agile flight allows them to pursue prey aerially too.
Population and Conservation
The Arctic tern has an extremely large global population estimated between 1-3 million adult birds. Trend data suggests Arctic tern populations are declining in Europe but increasing in North America.
Potential threats to Arctic terns include:
- Predation of eggs/chicks by foxes, gulls, skuas
- Disturbance of breeding colonies
- Oil spills, marine pollution
- Climate change affecting prey populations
However, the Arctic tern’s widespread range and ability to nest in remote polar regions means the overall population is very healthy. They are categorized as “Least Concern” on the IUCN Red List of Threatened Species. Protecting breeding sites and reducing marine pollution can help maintain numbers of this epic migratory bird.
Comparison with Other Birds
The Arctic tern’s migration is unmatched by any other bird species. Some comparisons:
Bird | Total Migration (km) |
---|---|
Arctic Tern | 90,000 |
Pomarine Jaeger | 48,000 |
Great Snipe | 26,000 |
Bar-tailed Godwit | 25,000 |
The Arctic tern flies much farther than any other migratory bird annually. Even other champion migrators like the Bar-tailed Godwit cannot match the Arctic tern’s feats.
The Arctic tern also experiences more daylight hours over the year than any other animal. This results from its pole-to-pole migration strategy that keeps it continually moving towards summer conditions in the north and south. No other vertebrate creature comes close to the 20+ daylight hours that Arctic terns can experience daily.
Records and Discoveries
Some notable records and discoveries about the Arctic tern include:
- Longest migration – Banded Arctic tern recorded flying over 96,000 km roundtrip from Alaska to New Zealand and back.
- Oldest known – Recaptured individuals over 30 years old, one 34 years old.
- Youngest crossing – Chick fledged from Maine colony retrapped weeks later thousands of miles away in Europe mid-migration.
- Fastest documented – Reached ground speeds over 40 mph with favorable winds.
- Furthest southing -tracked to 78 degrees south latitude, further south than any other tern species.
Tracking studies continue to reveal new insights into the Arctic tern’s range, speed and longevity. Recently, geolocator tags have mapped their circumpolar migration routes in more detail.
Significance of Long Migration
The Arctic tern’s extremely long annual migration is significant for several reasons:
- Incredible endurance – Shows physiology adapted for extreme long-distance flight over months.
- Navigation ability – Highlights complex navigational skills and abilities in birds.
- Sees more daylight – Experiences more annual daylight than any animal, up to 20 hours/day.
- Access to resources – Allows exploitation of abundant seasonal food at high latitudes.
- Avoids competition – Makes use of food in polar regions other birds can’t access.
Ultimately, the Arctic tern’s migration allows it to tap into ephemeral resources that support breeding in the high Arctic summer while avoiding competition from other birds. This underlies their strategy to achieve global success.
Conclusion
In summary, the Arctic tern is a consummate long-distance flyer uniquely adapted for lengthy migrations. Its extreme pole-to-pole migration is the longest yearly round-trip of any bird. This enables Arctic terns to experience more annual daylight than any other animal and take advantage of abundant seasonal food resources in both polar regions. While predation and disturbance pose threats to breeding colonies, the Arctic tern’s numerous populations across a circumglobal range ensure it remains a least concern species. Tracking technologies continue to provide new insights on these marathon migratory birds.