The Phenomenal 23,000-Mile Journey of Arctic Terns

The Arctic tern migration is a phenomenal 23,000-mile odyssey stretching from the Arctic to the Antarctic and back again. They literally travel from the top of the world to the bottom and back. This bird holds the title for the longest migration in the animal kingdom.

The Arctic tern’s big migration is more than just a regular trip they take every year. It’s a huge deal for the whole world’s ecosystem and illustrates how everything in nature is linked together. Research into their travel habits, behaviors, and challenges shows us we must start protecting them.

The Arctic Tern’s Extraordinary Voyage

The Arctic Tern, known scientifically as Sterna paradisaea, goes on one of the most awe-inspiring journeys in the animal kingdom. This small, slender bird with angular wings begins its migration from the Arctic Circle in late summer. The Arctic Circle is the northernmost part of the Northern Hemisphere. As the Arctic plunges into the cold, dark winter, these birds follow the summer southward to the Antarctic Circle. In this leg of the trip, they travel a staggering distance.

This distance is actually far more than the roughly 18,640 direct miles (30,000 kilometers) between these two extremes. This is because it is impossible for them to fly in an absolute straight line from north to south. In addition to flying the actual distance miles, they add on more miles to find suitable stopping points and avoid problematic areas.

The migration to warmer weather starts around September and they reach their destination in December. The Arctic terns spend 5-6 months enjoying the summer weather in the Southern Ocean (aka Antarctic Ocean). In April, the birds start the return journey to the Arctic Circle and arrive in May. The long, carefully planned, migration means Arctic terns are almost always in the sun. The migration from the Arctic to Antarctica has them living in constant summer. 

Arctic terns are uniquely adapted for long-distance flight. They prefer to glide on air currents to conserve energy. This adaptation allows them to cover great distances with minimal effort. They are so lightweight that ocean breezes can carry them vast distances without the need for frequent flapping. Arctic terns can even sleep and eat while gliding. Only a few other species share this rare ability (Hummingbirds can also hover in midair while they’re eating). It is thought this might be because they are practicing unihemispheric sleep, but this is proven yet.

Their migration is not a direct southward journey. These birds often fly thousands of miles off their intended path. They do this to take advantage of the best weather conditions. They also travel off-course seeking abundant food resources. This detour can lead them across every continent and significantly increase the total distance traveled. Their route is flexible to allow the best opportunities for food and good weather. Some Arctic terns originally from Siberia have been spotted as far away as South Africa. Others from Greenland have made appearances in Australia.

Comparative Flight Records

The Arctic Tern’s migration is monumental, not just in terms of distance but also in comparison to other migratory birds. The barn swallow (Hirundo rustica) and the sooty shearwater (Ardenna grisea) also undertake lengthy migrations. The sooty shearwater travels almost as far, but the Arctic tern holds the record for the longest migration.

In a recent study, an Arctic Tern was documented to have traveled approximately 59,650 miles in a year. This bird started from the Farnes Islands in Britain. It flew down to the tip of South Africa, then to the Indian Ocean, and finally arrived in Antarctica. It stayed in Antarctica for a bit, then repeated the whole trip in reverse. This record-breaking journey is equivalent to flying around the circumference of the Earth twice, plus an additional 10,000 miles.

Our knowledge of these extraordinary feats is made possible through the use of geolocators. These tiny devices track light levels and provide data on the bird’s location. They do this based on the timing of sunrise and sunset. This technology has revolutionized our understanding of the lengths to which these birds will go to follow their migratory instincts.

Tracking the Tern

Researchers have equipped Arctic terns with miniature archival light loggers. These are known as Mk14 geolocators and weigh 1.4 grams. These devices are attached to the birds’ legs using plastic rings. They add an overall weight of about 2.0 grams to the bird, which is approximately 1.9% of an adult tern’s body mass.

Geolocators were attached to 50 breeding terns in Northeast Greenland and an additional 20 in Iceland. The data retrieved from these geolocators has provided invaluable insights into the terns’ migration patterns. Notably, the researchers have successfully recorded a full year of migration data from 10 out of 11 devices. They tracked the birds’ locations for an average of 207.2 days per year.

The geolocators are particularly useful for tracking the terns’ movements across vast distances. However, they have limitations. They don’t work well during periods of continuous daylight at high latitudes. This is true around equinoxes when only longitude data can be collected. Despite these challenges, the devices have uncovered previously unknown stopover areas. They have also detailed the birds’ extensive use of global wind systems to optimize their flight paths.

The potential for using GPS satellite transmitters to track Arctic terns offers a promising expansion of current capabilities. The current geolocators provide valuable data on light levels. However, they underestimate the total distance flown by the birds due to their method of recording only daily positions. Researchers anticipate that smaller GPS devices could reveal even more extraordinary distances traveled by these birds.

A GPS device would allow for continuous tracking of their precise locations. However, developing GPS technology light enough for small birds is a challenge. It has to be small and light enough to not impact their normal behaviors and migration efficiency.

Factors Influencing Migration

Climate change significantly impacts Arctic tern migration. This is mainly due to its effect on polar regions where these birds live. The terns rely on productive marine areas for foraging. They use sea ice for rest and foraging. And, good prevailing winds support them during their extensive flights.

Changes in the productivity of oceans occur because of the rate of organic matter produced by phytoplankton. These changes influence the availability of key prey species like krill. During their southbound migration, Arctic terns adjust their flight speeds in regions with high food availability. They have to be opportunistic feeders on these long journeys.

Sea ice plays a crucial role in the Arctic terns’ lifecycle, especially during the non-breeding season. They often reside within fragmented sea ice zones. These zones are rich in Antarctic krill and provide essential feeding grounds. However, projections suggest a significant decline in krill spawning is coming soon due to sea ice loss. The decline in krill could severely impact the tern population.

Additionally, wind conditions are subject to changes due to climate shifts. Wind conditions influence flight efficiency by providing favorable air currents. If they change significantly, it could potentially alter migration patterns and routes.

The energy demands of migration are incredible. The physical exertion required for such journeys is immense. Terns need to eat a lot to sustain energy levels and keep flying. Food availability is affected by environmental changes and may require them to use more energy to find food. This impact on food availability can directly affect migration routes. For example, declines in North Atlantic food resources will likely challenge the terns’ foraging during their migration. And, this may lead to increased energy expenditure to locate sufficient food.

Minor changes in wind speeds may seem insignificant. However, even small shifts can influence the terns’ ability to maintain efficient flight paths. Enhanced westerlies in the Southern Ocean could force terns to adjust their routes or flight strategies. This, in turn, potentially increases the energy costs of migration.

Arctic Tern Conservation

Historically, Arctic terns faced severe threats from human activities. This was particularly apparent during the nineteenth century when millions were hunted for their feathers to adorn women’s hats. Today, they are not considered endangered.

This is mainly because their remote breeding grounds in the high Arctic offer some protection from direct human interference. These areas are so isolated and cold. Even natural predators such as the Arctic fox have difficulty locating their nests. However, human-induced climate change is a significant, indirect threat to these birds. The changing climate will impact their migration patterns and the availability of their food sources.

Effective conservation efforts are critical to mitigate the impacts of climate change and ensure the survival of Arctic terns. It is imperative to protect their nesting habitats. These nesting areas include the rocky and sandy beaches of the Arctic and subarctic regions.

Other key conservation methods include minimizing human disturbance and preventing habitat degradation. Removing invasive species, such as the American mink, has also proven successful in preserving tern nesting areas. Minks pose a significant risk to tern eggs and chicks. Their control is vital for the terns’ survival.

Conservation actions must also address the broader environmental challenges posed by climate change. For instance, the decline in krill populations due to reduced sea ice is a considerable concern that requires urgent attention.

Interesting Facts About Arctic Terns

1. Arctic terns only nest once every 1-3 years
2. Many Arctic terns reach up to 30 years of age.
3. Arctic terns are monogamous. They choose one mate for a lifetime.
4. Baby terns can fly within 15-25 days.
5. Arctic terns are waterbirds, but they have very small webbed feet. This means they are not great swimmers. Their time in the water is limited to as long as it takes to get a bite of food.

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Cover Photo: ID 31706928 | Arctic Terns © David Head | Dreamstime.com