The Arctic tern undergoes the longest migration of any bird in the world. This incredible seabird breeds in the Arctic during the summer months, then migrates down to the Antarctic for the winter, with some individuals flying over 90,000 km round trip each year. But just how long does this epic journey take from start to finish?
The Arctic Tern’s Range
The Arctic tern has a circumpolar distribution, meaning it can be found breeding in Arctic and subarctic regions all the way around the northern hemisphere. The main breeding range includes northern parts of Europe, Asia, and North America – areas like Iceland, northern Scandinavia, Russia, Alaska, and Canada. Meanwhile, the wintering grounds are concentrated around the Antarctic coastline and nearby islands.
This means an individual Arctic tern nesting in Alaska could potentially fly all the way to the Weddell Sea on the eastern side of the Antarctic Peninsula – a staggering 19,000 km one way! Of course most birds won’t travel quite that far, but marathon migrations of over 90,000 km round trip are still common.
Length of Migration
So just how long does it take the Arctic tern to complete these amazingly long migrations? Research shows that most birds travel between their Arctic breeding grounds and Antarctic wintering areas in around 6 months each way.
Studies using geolocators attached to the birds have found autumn southward migrations last an average of around 2.5 months. Meanwhile, the return northward journey in spring takes approximately 3 months. This adds up to a total migration time of around 6 months in each direction.
Autumn Migration
After the breeding season ends in late summer, Arctic terns gather in large flocks and begin migrating south. The first leg of the journey involves flying over land across northern Eurasia or North America to reach coastal areas.
From there, the terns fly south over the Atlantic Ocean to reach Antarctica and nearby islands. Most birds reach their wintering grounds sometime between late September and early December. Peak arrival times are usually in October and November.
Satellite tracking studies have shown the autumn migration can cover 200-300 km per day on average. But speeds vary depending on weather conditions and other factors. Some terns may fly up to 500 km in a single day with favorable tailwinds.
| Month | Migration Details |
|---|---|
| Late August – September | Terns depart Arctic breeding grounds and migrate south over land |
| September – November | Main migration over Atlantic Ocean to Antarctica |
| October – November | Peak arrival at Antarctic wintering areas |
Spring Migration
The northward migration to the Arcticbreeding grounds begins in late February and March. The terns follow a similar route in reverse – first flying north over the Atlantic from Antarctica, then later over land to reach the Arctic coast.
Spring migration is faster overall compared to autumn. The terns are traveling with the prevailing northerly winds, and are in a hurry to reach the breeding grounds to establish territories and find mates.
Satellite tracking has recorded migration speeds over 500 km per day during spring, especially over ocean areas. Most birds reach the Arctic by late May or early June in time for the brief summer breeding season.
| Month | Migration Details |
|---|---|
| February – March | Depart Antarctic wintering grounds and begin migration north |
| March – May | Main spring migration over Atlantic Ocean |
| May – June | Arrival at Arctic breeding areas |
Total Migration Time
By combining the autumn and spring migration periods, we can estimate that the total time for the Arctic tern’s complete round trip migration is around 6 months in each direction, or roughly 12 months (1 year) total. Some key points:
- Autumn migration lasts around 2.5 months on average
- Spring migration lasts around 3 months on average
- Total migration time is around 6 months each way, or 12 months round trip
- Actual travel times for individual birds depend on weather, route, breeding status, etc.
- The longest migrations can be up to 90,000 km round trip!
So in summary, most Arctic terns take around 6 months to complete their phenomenal pole-to-pole migration, but can spend up to a full year on the journey when accounting for the complete round trip. This epic feat makes the Arctic tern a true champion of the animal kingdom when it comes to endurance long-distance migration!
Incredible Navigation
The ability of the Arctic tern to navigate tens of thousands of kilometers during its migration is incredible. Here are some of the ways the Arctic tern navigates during its migration:
Using the Sun’s Position
Arctic terns use the sun as a guide to maintain their direction of travel. By understanding the sun’s position in the sky relative to the time of day and year, the terns can orient themselves on a north-south axis.
Detecting Earth’s Magnetic Field
The Arctic tern can sense the Earth’s magnetic field through an internal compass-like system. This allows them to determine direction even on cloudy days when celestial cues are unavailable.
Using Landmarks
Landscape features like coastlines, rivers, mountains, and islands can serve as visual landmarks to help Arctic terns confirm their migratory route.
Following Ocean Currents
By detecting gradients in water temperatures, Arctic terns can follow favorable ocean currents on their migration route over water.
Using Sense of Smell
Arctic terns may also use their sense of smell to help navigate towards land after long periods out at sea.
Challenges Along the Route
During their extremely long migrations, Arctic terns face many challenges along the way that can impact their journey time. Some of the main obstacles they must overcome include:
Harsh Weather
High winds, ocean storms, and precipitation can slow the terns’ progress and force them to seek shelter. This has the biggest impact during sea crossings.
Lack of Food
Finding adequate food to refuel during migration can be difficult, especially over long stretches of ocean. Lack of food may limit terns’ energy for migrating quickly.
Predation
Predation danger from birds like jaegers and skuas forces Arctic terns to be vigilant, reducing migration speed.
Exhaustion
The extreme distances covered take a toll physically and the terns need to rest periodically during migration. Their energy reserves may become depleted.
Disorientation
Navigation errors and getting off course can cost time as terns have to correct their directional mistakes.
Unbelievable Physiology
The Arctic tern possesses a number of remarkable physiological adaptations that enable it to complete its marathon migration each year. A few examples include:
Lightweight Body
Weighing in at only 90-120 grams, the Arctic tern’s small size and lightweight body is energy-efficient for flying extraordinary distances.
Long Wings
With a wingspan around 75-85 cm, the Arctic tern’s long, narrow wings allow superb aerodynamics and gliding ability for sustained flight.
High Metabolism
A ramped-up metabolism allows Arctic terns to efficiently burn through fat reserves to fuel endurance activity over thousands of miles.
Water Resistance
Water-repellent feathers help keep the Arctic tern dry and buoyant during periods sitting on the ocean surface.
Salt Excretion
Special glands above the eyes remove excess salt from the body – an adaptation to marine environments.
Complex Life Cycle
The Arctic tern’s migration is connected to its breeding cycle in a complex way that influences how long the birds spend on migration compared to stationary periods.
Short Summer Breeding
Only 2-3 months are spent on Arctic breeding grounds in frantic mating and raising young before migrating south.
Wintering at Sea
Months are spent feeding at sea in Antarctic and southern latitudes before returning north.
Long Absences
Arctic terns may only visit breeding colonies for a few months total over several years in between migrations.
Late Maturation
Arctic terns don’t breed until 4-5 years old, spending years developing and migrating before settling down.
Lifetime Migration
The cycle continues for over 20 years – the Arctic tern’s entire adult lifespan is spent migrating year-round.
Comparison to Other Birds
The Arctic tern makes one of the longest migrations in the animal kingdom, far surpassing most other migratory birds. A comparison:
| Bird | One-way Migration Distance | Total Round Trip |
|---|---|---|
| Arctic Tern | Up to 30,000 km | Up to 90,000 km |
| Pied Flycatcher | 5,000 km | 10,000 km |
| Ruby-throated Hummingbird | 3,500 km | 7,000 km |
| Bar-tailed Godwit | 11,000 km | 22,000 km |
| Hudsonian Godwit | 9,000 km | 18,000 km |
The extreme marathon migrations of the Arctic tern are in a league of their own when compared to even the most well-traveled birds. The Arctic tern is truly the ultimate global wanderer!
Record-Breaking Migrations
Using tracking technology, scientists have been able to document some of the longest Arctic tern migration routes ever recorded:
- One Arctic tern tracked between Wales and Antarctica covered 96,000 km roundtrip in 11 months – the longest recorded migration at the time.
- An Arctic tern tagged in the Netherlands reached Australia, over 22,000 km away within just 3 months.
- A young Arctic tern flew from The Netherlands to Melbourne, Australia – over 22,000km nonstop, likely the longest nonstop flight ever recorded for a bird.
- Another Arctic tern flew from Alaska to New Zealand and back – covering around 91,000 km total roundtrip distance.
These record-breaking tracks demonstrate just how far the incredible Arctic tern is capable of traveling each year. Even the most extreme migrations highlighted here likely only scratch the surface of the Arctic tern’s astounding long-distance flying abilities.
Threats and Conservation
Despite its impressive resilience in undergoing such a strenuous two-part annual migration, the Arctic tern still faces a number of conservation threats to its survival. Some of the main threats include:
Climate Change
Warming temperatures in the Arctic and Antarctic may reduce habitat suitability in breeding and wintering grounds over the long term.
Commercial Fishing
Drowning in fishing nets is a risk, especially for young birds on their first migrations.
Pollution
Ocean plastic pollution and oil spills can contaminate food sources and Arctic tern habitats.
Disturbance
Human disturbance, such as trampling nests on breeding colonies, can reduce reproductive success.
Predation
Predation of eggs and chicks by foxes, gulls, and other animals may be increasing in some regions.
Protecting both Arctic and Antarctic ecosystems will be important for conserving the Arctic tern into the future. Limiting further human impacts in remote polar regions used by these global migrants can help ensure their extraordinary migrations persist.
Conclusion
The Arctic tern’s annual odyssey stretching from pole to pole is one of the most incredible feats of endurance in the natural world. Powered by amazing physiology and navigation abilities, most terns complete their 30,000+ km migrations in around 2.5-3 months each way. Total migration time clocks in at an estimated 6 months in each direction, or 12 months round trip to breed, feed, rest, and reach the limits of the Earth’s latitudes. While facing numerous challenges from weather, predators, finding food, and more, the hardy Arctic tern persists, returning year after year to continue its lifetime pattern of perpetual global wanderlust. This marathon migrant truly earns its title as the ultimate frequent flyer of the bird world!
