The Arctic tern (Sterna paradisaea) is a fascinating seabird known for its incredibly long migration. Here are some of the most unique facts about these extraordinary birds:
The Longest Migration of Any Animal
Arctic terns have the longest migration of any animal on Earth. They breed in the Arctic during the summer months then migrate all the way to the Antarctic for the winter. This journey covers over 25,000 miles round trip each year. That’s like flying from New York to Perth, Australia and back every year!
It’s estimated that over a lifetime, some Arctic terns may travel over 1 million miles during their migrations. That distance is equivalent to flying to the moon and almost halfway back. Their extreme travels are possible because of the abundance of food sources along their migration route and the fact that they stay in constant daylight for most of the year, not having to stop due to nightfall.
They See More Daylight Than Any Other Animal
Thanks to their pole-to-pole migration, Arctic terns experience more annual daylight hours than any other animal on the planet. From early spring through late summer, the regions of the Arctic and Antarctic where the terns breed and feed experience 24 hours of sunlight per day. This allows the birds to hunt and feed their chicks nearly non-stop during the breeding season.
It’s estimated that the Arctic tern sees more daylight over its lifetime than any other living thing on Earth. While humans average about 25,000 days over an 80-year lifetime, the Arctic tern enjoys over 100,000 days of daylight in its 30+ year lifespan.
They Have the Longest Lifespan of Any Seabird
In addition to their migratory feats, Arctic terns also hold the longevity record for seabirds. They can live for over 30 years in the wild, far surpassing the average seabird lifespan of 10-15 years. Their long lives allow them to complete tens of thousands of miles in migration annually.
Scientists have banded Arctic terns and recaptured them as many as 27 years later, still actively nesting and migrating each year. The oldest known Arctic tern was at least 34 years old when it was found in the Netherlands. But researchers suspect they may live even longer than that in some cases.
They Defend Their Nesting Territory Ferociously
While Arctic terns only weigh about 100-125 grams, they are fiercely defensive of their nesting colonies and young. Their aggressive behavior earned them the nickname “sea swallows” because of how they attack any intruders like dive-bombing swifts.
Both males and females participate in aggressive swooping and diving attacks on any animals or humans that get too close during breeding season. They will target heads and eyes and have drawn blood on occasion. Their feisty behavior helps protect eggs and chicks from predators.
They Have Unique Migration Strategies
Scientists have uncovered some fascinating facts about how Arctic terns manage to complete their amazingly long migrations each year:
- They fly huge loops rather than straight routes to take advantage of global wind patterns.
- They gain flight power by locking their wings and gliding 20-30 feet between wing flaps.
- They can navigate by sensing magnetic fields to stay on course.
- They can fly up to 500 miles in a single day at speeds around 30 mph.
Their flight strategies allow them to complete roundtrip migrations using the least amount of energy possible. Some individuals only weigh around 80 grams but still complete the entire journey.
They Sometimes Take Mid-Journey Breaks
Even these champion fliers need to occasionally rest and refuel. Some Arctic terns take breaks that can last several days at certain stopover sites along their migration route. For example, they’ve been observed stopping in the Faroe Islands, Iceland, and off the coast of West Africa to rest and feed before continuing their journey.
These pitstops allow the birds to feed and wait for favorable winds before crossing long stretches of ocean. By taking intermittent breaks, the terns ensure they have enough energy reserves to complete their grueling pole-to-pole migration.
They Forage While Migrating
Another key strategy Arctic terns use to fuel their migration is foraging while on the move. They will dive down to capture fish and other small prey from the ocean surface as they fly over their migratory route.
This allows them to build up fat stores and food energy continuously along the journey. Unlike some birds that don’t eat at all while migrating, the Arctic terns are able to be highly efficient migrant fliers because they can eat on the go.
They Breed in Huge Colonies
Arctic terns nest in very large groups numbering in the thousands or even tens of thousands of breeding pairs. Some of the biggest colonies holding over 20,000 terns are found in the Faroe Islands, Iceland, Greenland, and Russia.
Nesting in huge groups provides more security from predators like foxes and large gulls. And the massed ranks of terns can fight off threats more effectively with their dive-bombing attacks when all the birds join in together.
They Have High Site Fidelity
Arctic terns exhibit a strong attachment to their breeding colonies and will return to nest in the exact same location year after year. Even though they migrate huge distances, they have incredibly accurate homing instincts that allow them to find their way back to their colony of origin.
This high breeding site fidelity means they will loyally return to nest alongside the same mate in the same location for many seasons in a row. Their natural homing abilities are still not fully understood by researchers.
They Sometimes Switch Between Fresh and Saltwater Habitats
Most Arctic terns spend their lives solely in marine environments. But some inland-nesting colonies will forage in freshwater lakes, rivers or ponds near their nesting grounds. This adds dietary flexibility, allowing them to hunt the most readily available fish and insects.
In Greenland, researchers found terns that were nesting near freshwater would switch between marine feeding flights and local freshwater foraging. Their adaptability allows them to raise chicks whatever the local conditions.
They Are Strong, Acrobatic Fliers
Watching Arctic terns fly is a sight to behold. They have very long, slender wings and tails to provide maneuverability and gliding ability. Their flight style is graceful, buoyant and effortless looking.
Terns are also highly aerial acrobats. They can hover, dive, loop upside down, plunge directly into the water after prey, and flip in mid-air with amazing agility. All these aerobatic skills aid their fishing and help them evade predators.
They Sometimes Follow Ships to Find Food
An easy meal ticket for Arctic terns during migration is trailing fishing boats and trawlers. The boats will drive fish toward the surface, making them easy pickings for the terns. Some individuals learn to reliably join certain ships that provide regular feeding opportunities.
Researchers found terns using this strategy increased their fat stores and survival compared to ones only foraging naturally. Their opportunistic feeding gives them extra energy for the long haul migration flights.
They Have Unusual Migration Timing Compared to Other Birds
Most Northern hemisphere bird species migrate north to their breeding grounds in spring, then south to warmer areas for winter. But the Arctic tern’s migration is opposite to this pattern.
After breeding in the Arctic summer, they make their longest migration leg south to Antarctica in the Southern hemisphere fall and winter. Then they head north back to the Arctic as Antarctic winter ends and Arctic summer begins. Their unique timing maximizes time in peak feeding areas.
They Sometimes Breed Among Antarctic Penguins
In Antarctica, Arctic terns will often nest alongside penguin colonies for added protection. The massed penguins help shield the terns from Antarctic aerial predators like skuas and giant petrels looking for an easy meal.
In turn, the aggressive terns help defend the penguin chicks and eggs from these same predators with their dive-bombing. This shows how different polar species can provide each other mutual benefits in the harsh Antarctic climate.
They Have Several Predator Defense Strategies
Arctic terns have evolved various defensive tactics to help their chicks survive against predators:
- Nesting in large groups for security in numbers.
- Aggressively mobbing intruders.
- Distraction displays leading predators away from nests.
- Camouflaged eggs and chicks to avoid detection.
- Frequent changeovers at the nest by parents.
- Nesting on isolated islands away from main predator ranges.
Multiple layers of protection mean tern colonies can withstand attacks and still successfully rear chicks despite losses to predators.
They Sometimes Breed Before Reaching Adult Plumage
Most young Arctic terns spend their first 2-4 years on migration and reaching full adult plumage before first breeding. But when food conditions allow, some 1-year-old terns will try to breed while still in transitional grey/white juvenile plumage.
Though less common recently, Norwegian researchers observed many immature terns attempting to breed back in the 1930s when food was abundant. Their flexibility in adapting breeding age helps maximize reproductive success in highly variable environments.
They Are Highly Sensitive to Disturbance
The ground-nesting habits of Arctic terns make them very vulnerable to disturbance from humans. Even a small amount of disturbance like a single destructive visitor can cause mass colony abandonment.
Conservation efforts now limit access to tern colonies during breeding season. Careful management is required as terns will readily abandon nests full of eggs if feeling overly threatened by encroaching activity.
They Sometimes Change Migration Route Due to Wind Conditions
Arctic terns rely on favorable tailwinds that boost their migration speed and efficiency. When wind conditions along their usual route are unfavorable, they are able to shift their route to find faster steaming winds.
For example, researchers found terns avoiding headwinds on their normal coastal path by taking a detour several hundred miles offshore to catch faster winds. This allows them to complete their migration using the least amount of energy.
They Have Developed Special Salt-Excretion Glands
Arctic terns have adapted a unique gland system to cope with drinking saltwater. Located above their eyes, these specialized glands help eliminate excess salt from the body that the birds ingest while feeding at sea.
The glands filter and excrete concentrated salt solutions, allowing the terns to maintain proper electrolyte balance. This helps them thrive and feed far from land on long migratory journeys over ocean waters.
They Sometimes Blow Hundreds of Miles Off Course
Navigational failures happen to even the most accomplished seabirds like the Arctic tern. Wind conditions or geomagnetic disturbances can knock them seriously off their normal migration route.
There are records of vagrants showing up hundreds or thousands of miles from normal range due to getting lost and blown drastically off track. Most fail to find their way back and will not return to their original colony site if they manage to survive.
They Have Experienced Population Declines in the Past
Threats from human activity caused significant drops in world Arctic tern numbers during the 19th and early 20th centuries. Disturbance of breeding colonies, feather harvesting, and excessive egg collecting led to alarming declines.
Thankfully, conservation efforts have allowed their populations to rebound in many regions. Ongoing monitoring and protection are critical to ensure these epic migrants don’t become endangered again in the future.
Their Conservation Status Varies Greatly by Location
Currently, Arctic tern conservation status ranges from Least Concern to Critically Endangered based on geographic location of different breeding populations:
| Location | Conservation Status |
|---|---|
| Europe and Western Siberia | Least Concern |
| East Siberia | Near Threatened |
| North America | Least Concern |
| Faroe Islands and Iceland | Least Concern |
| Greenland, Svalbard, Norway | Near Threatened |
| Turkmenistan through China | Vulnerable |
| Chatham Islands | Critically Endangered |
Maintaining protections for breeding colonies is vital to prevent any populations from slipping into endangered status.
Conclusion
The Arctic tern is a true champion of the animal kingdom due to its extraordinary migration, remarkable endurance, and unique survival adaptations. This marine acrobat and feisty nest defender continues to fascinate ornithologists and birdwatchers alike. Careful ongoing conservation efforts are needed to protect the tern’s Arctic and Antarctic breeding havens so these epic global wanderers can thrive for centuries to come.
