Arctic terns are seabirds that are known for their incredibly long annual migrations. One of the most unique characteristics of Arctic terns is their migratory range, which is the longest of any bird species. Every year, Arctic terns make a round trip journey of around 70,000 km (43,000 miles) between their Arctic breeding grounds and their wintering grounds in the Antarctic. This extreme migration is a unique adaptation that allows Arctic terns to experience endless sunlight during the Arctic summer and avoid the winter darkness.
What Makes Arctic Terns’ Migration Unique?
Arctic terns have the longest migration of any animal on Earth. Here are some key facts about their incredible journey:
- Arctic terns breed in the far north Arctic during the summer months when there is 24 hours of daylight.
- In the fall, they migrate south all the way to the Antarctic coast for the summer and to avoid the dark Arctic winter.
- The total trip is around 70,000 km (43,000 miles) each way.
- No other migratory bird comes close to matching the Arctic tern’s migratory range.
- The total journey would be equal to flying 3 times from the Earth to the Moon and back.
- Arctic terns see more daylight than any other creature on Earth.
- They experience 2 summers and more total daylight than if they stayed in either habitat alone.
This extreme migration allows Arctic terns to take advantage of the most favorable breeding and feeding grounds. By migrating, they are able to avoid harsh winters with no daylight and capitalize on endless summer sunlight in both polar regions.
Breeding in the High Arctic Summer
Arctic terns breed in the far northern reaches of North America, Europe, and Asia. Their breeding grounds extend as far north as there is land before the permanent Arctic ice cap.
Here are some key facts about their Arctic breeding season:
- Nesting occurs between June and August.
- During this time, the high Arctic has 24 hours of daylight.
- Abundant food like fish, shrimp, and invertebrates is available to feed chicks.
- Breeding coincides with peak marine productivity.
- Endless daylight allows maximum time for foraging and feeding chicks.
The 24 hours of Arctic daylight provides ideal conditions for raising chicks. Arctic terns can continuously hunt and bring back food to their nests without being limited by darkness. The nonstop sunlight maximizes their ability to reproduce successfully.
Wintering in the Antarctic Summer
After breeding and raising chicks to fledging, Arctic terns migrate south in the fall to reach their wintering grounds in Antarctica by December. Here are key facts about their time in the Antarctic:
- They arrive in December-January when Antarctica has 24 hours of daylight.
- Abundant krill, fish, and squid provide plentiful food.
- Ice-free coastal waters provide access to food supplies.
- The Antarctic summer has huge phytoplankton blooms that support Antarctic food webs.
- Again, 24 hour daylight allows maximized feeding.
Spending the southern hemisphere summer in Antarctica under endless daylight provides ideal conditions for the terns to rest, molt, feed, and prepare for their impressive northbound migration.
Nonstop Travel
Perhaps most incredibly, Arctic terns make their migration between polar regions in huge nonstop segments. They fly hundreds or even thousands of miles at a stretch without stopping to rest or feed.
- They fly 500-600 miles per day on average.
- Some studies using geolocators found the terns can fly for multiple days and over 2000 miles nonstop over ocean waters.
- Their migration includes the longest nonstop segment of any animal at around 4000-6000 miles over the Atlantic Ocean.
- Their straight-line route means arctic terns pass over nearly every country of the world.
This nonstop travel allows the terns to complete their extreme pole-to-pole migration efficiently. They are designed for sustained long-distance flight powered by their high-calorie fish diet. Their unique biology makes their marathon global migration possible.
Unique Adaptations for Extreme Migration
Arctic terns possess many unique physiological and morphological adaptations that enable their extremely long seasonal migration between the polar regions. Here are some of their key adaptations:
Aerodynamic Body
Arctic terns have a distinctly aerodynamic body optimized for sustained long-distance flight:
- A streamlined, narrow-winged silhouette reduces drag.
- Long, pointed wings provide lift and efficiency in flight.
- A short, forked tail decreases air resistance.
- Lightweight bones and minimal body fat improve flight performance.
High Metabolism
Arctic terns have a boosted metabolic rate to support high energy needs for endurance flight:
- Higher mass-specific metabolic rate than similar-sized seabirds.
- Increased thyroid hormone levels boost their metabolism.
- More red blood cells transport greater oxygen for energy.
- Powerful breast muscles drive sustained wingbeats.
Orientation and Navigation
Specialized abilities guide Arctic terns on their remarkably precise migrations:
- Sensitive vision adapts to extreme day lengths in polar regions.
- Ability to orient using the sun’s position even on cloudy days.
- Possible use of Earth’s magnetic field for orientation cues.
- Large hippocampus region of the brain for spatial memory.
Fuel Storage
Arctic terns can store enough fat reserves to fly huge distances nonstop:
- Build up fat deposits before migratory flights.
- Carry extra fuel loads exceeding 50% of their body weight.
- Burn fat stores slowly and efficiently in flight.
- Digestive system shrinks to reduce weight and free up space for fuel storage.
These specialized adaptations allow Arctic terns to achieve their marathon global migration between the polar regions each year. Their biology is finely tuned to enable some of the longest nonstop endurance flights in the animal kingdom.
Threats and Conservation
Despite their long migrations away from most human activity, Arctic terns still face a number of conservation threats:
Climate Change
Warming oceans and melting sea ice in the Arctic and Antarctic may impact food availability and breeding habitat. Rising sea levels can flood nesting sites.
Disturbance
Tourism activities, research, fishing, and development near breeding colonies can disrupt nesting birds. Restricted access helps minimize disturbance.
Predators
Predatory gulls, foxes, polar bears, and other animals may feed on eggs or chicks. Monitoring and predator control helps protect nesting colonies.
Pollution
Ocean plastic debris and oil spills can contaminate feeding areas. Pesticides and heavy metal pollution may build up in their bodies.
Fisheries Interactions
Arctic terns can get caught on longline hooks or in fishing nets. Using bird-safe fishing methods reduces bycatch mortality.
Protecting breeding habitat, minimizing disturbances, and reducing ocean threats helps support Arctic tern populations. Their extreme global migration makes international cooperation critical for effective conservation.
Conclusion
The Arctic tern’s annual pole-to-pole migration is a remarkable feat of endurance unmatched in the animal world. By traveling up to 70,000 km between Arctic and Antarctic polar habitats, Arctic terns experience more annual daylight than any other creature. Their specialized adaptations for extreme long-distance flight enable this impressive nonstop global journey. As human impacts reach even the most remote regions, continued conservation efforts are needed to ensure the survival of these champion migrants flying ceaselessly between the ends of the Earth.