The Arctic tern (Sterna paradisaea) is a bird species that has long been held in awe for its incredible migrations between the North and South polar regions. Amazingly, recent studies have shown that these birds travel much further than previously thought.
The Arctic tern undergoes the longest migration of any animal species on Earth. These superlative birds can travel a distance equivalent to the moon and back three times during the course of their lives. Let that sink in for a minute!
Scientists are still working on putting all the pieces of the puzzle together, but much has been uncovered about their migration. This article covers their incredible journey and gives you a glimpse into the lives of one of nature's most amazing bird species.
Read on to learn how, when, and why these birds migrate.
A large flock of Arctic terns in flight
Arctic terns usually migrate over the open ocean, but they have been recorded traveling over land as well. While they often fly low, just over the surface of the water and the crests of waves, they can migrate at altitudes of nearly 10,000 feet.
Arctic terns are built for the air. These graceful birds weigh just 4 ounces or so but have a perfectly streamlined body shape that can be used for both powerful direct flight and effortless long-distance gliding.
They are smart about how they travel, too, often using tailwinds to save energy. On their way south after breeding, they don’t appear to be in too much of a hurry either, often traveling in meandering routes that take them through good feeding grounds and weather conditions.
The return trip seems to be taken with a little more urgency, and the birds take an S-shaped route up over the Atlantic ocean. The shape of the route is explained by the prevailing winds on either side of the equator.
Arctic Tern in flight over the Shetlands, UK
Arctic terns spend about four months of the year in active migration between their summer breeding area and overwintering grounds. Their southward migration typically takes place during the fall months, while their return trip takes place in the spring.
Arctic tern migrations have been studied using tiny instruments known as geolocators that are attached to the birds’ legs. Data collected this way, and by other observations, have helped us put together a picture of the timing of their migrations.
Read on for a look at a typical year in the life of the Arctic tern.
A group of Arctic terns hunting in Iceland
Arctic terns need to migrate each year because the polar winters are too dark for them to hunt. These birds hunt by sight by plunging into the water for small fish, crustaceans, and insects. The clever solution to this seasonal problem is to follow the sun, just like so many other migrants.
The Arctic may provide rich feeding and safe breeding grounds for Arctic terns in the summer, but these conditions change dramatically as the year progresses. At those latitudes, the day length varies greatly, creating summer days when the sun never really sets and perpetually dark winters!
Arctic terns migrate from the Arctic circle in the north to the Antarctic in the south, and back each year. This distance is roughly 25,000 miles (40,000 km) but since these birds do not fly in a straight line, the actual distance they travel is much further. Some individuals have been tracked to travel 56,000 miles (90,000 km) in a single year!
This is the longest migration of any bird. The actual distance of total migration varies a lot between individuals and the location of their breeding sites. These birds are not too rigid about the routes they take either, and they will happily take long detours if it means meeting up with better weather or food sources along the way.
It's thought that it requires around 30,000 kJ or energy of Arctic terns to complete their annual migration trips.
An Arctic tern perched on a rock
One of the fascinating things about Arctic tern migration is the variation in routes these birds take. The southward leg of the Arctic tern migration takes far longer than the northward return trip. It usually takes the birds about 3 months to reach their wintering grounds in the south, but just 40 days or so to return to their breeding grounds.
Arctic Terns usually migrate at heights of between 1,000 and 3,000 meters at a flight speed of up to 55 km/h (15 m/s).
Arctic terns do not complete the whole journey in one go and are known to stop over at staging areas and locations where food resources are abundant. They might stick around for as long as a month before continuing on their way.
Migration uses up so much energy that naturally these birds must feed along the way. Nevertheless, they have been recorded to travel as far as 5,000 miles, all while feeding on the go and not spending much time in any single area.
When on their northward migration journey, Arctic terns can travel at rapid speeds of over 500 km in a single day.
Arctic tern in flight
Arctic terns often migrate in small groups of 6 to 7 birds on average. They have also been recorded migrating singly, however, as well as in groups of as many as 70 birds.
Although their migration routes and breeding sites do vary somewhat, all Arctic terns breed at high latitudes in the Arctic regions of the northern hemisphere and migrate south for the winter.
Arctic terns foraging for food
Arctic terns head south after breeding in the Arctic to avoid the harsh northern hemisphere winter. By the time winter is in full swing, most of these birds are enjoying the long sunny days in the Antarctic region. This is the summer season in the southern hemisphere, a time when the birds have easy access to rich sources of small fish and crustaceans to feed on.
Arctic terns spend the northern summer in the circumpolar Arctic. This large area includes parts of Alaska, Canada, Greenland, Iceland, Scandinavia, and Russia. Amazingly, a very large majority of adult terns return to nest near the exact site where they were born.
Arctic terns travel more distance than any other bird species each year
The Arctic tern is known as the champion of migration because it holds the record for the longest distance traveled each year by any bird. This isn't a once-off migration either. These little birds can live for more than three decades, making their bodies a wonder of endurance.
Thanks to their amazing migrations, Arctic terns are able to live and breed in some of the harshest environments on Earth by perpetually following the warmth of summer.
Arctic terns migrate at all times of the day, including after dark. In the north, they have been recorded flying at high altitudes at night, using tailwinds to save energy. In the Antarctic regions, however, night flight was rarely recorded.
Research suggests that the Arctic tern population stands at about 2 million individuals. They are considered a Least Concern species, although their population trend is decreasing.
Arctic terns are ground-nesting birds. They may be incredible travelers, but they aren’t the best nest-builders in the bird world. They typically lay their eggs on stony or sandy ground within about 350 feet of the water’s edge.
Arctic terns are relatively long-lived birds for their size and healthy individuals can live for over 3 decades. In fact, the oldest recorded individual lived at least 34 years.
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