With round-trip flights between the Arctic and Antarctica of tens of thousands of kilometers each year, Arctic terns hold the title of longest migratory species.
Every year, Arctic terns (Sterna paradisaea) all embark on a journey to follow the summer Sun, moving along the length of the globe, from the upper regions of the Northern Hemisphere to Antarctica. With round trips of more than 30,000 km per year, they become the record holder for the longest migration in the animal world.
The shortest distance between their two seasonal habitats is nearly 19,000 km, but the journey is not always smooth. The 8,000 km trip across the Indian Ocean is said to be the most difficult leg. This leg requires Arctic terns to fly for 24 days, during which they face a variety of threats such as unpredictable weather patterns, turbulent waters, commercial fishing and plastic pollution.
Some animals choose longer routes than others, for reasons that are sometimes unclear. In 2016, an Arctic tern covered a record distance of 96,000 km in a round trip – more than twice the circumference of the Earth. It circled from northern England, down the west coast of Africa, across the Indian Ocean, into Antarctica and along the coast to the Weddell Sea. Then it returns to the Northern Hemisphere just in time for the breeding season.
Arctic terns are medium-sized seabirds, weighing only about 100 grams. They often gather in noisy groups to nest along the coast, often on sandy or pebble beaches. With their angular wings and slim bodies, they are well adapted to traveling long distances.
In the summer in the Northern Hemisphere, they live in the Arctic and sub-Arctic regions of Eurasia and North America, sometimes spreading to places as far south as Northern France and Massachusetts, USA. They will stay here from April to September, gathering in large flocks with many pairs nesting and breeding.
In the fall, Arctic terns begin to migrate south. Because of their Northern Hemisphere summer experience and the constant sunshine of the Antarctic summer, they enjoy more daylight than any other animal on the planet.
However, like many other seabirds, their transpolar journey is showing signs of being disturbed by climate change.
“Arctic terns get their food from resource-rich oceans, they also rely on sea ice for resting and foraging, and on prevailing winds during flight. Although Arctic terns are a ‘few species’ of concern’ on the International Union for Conservation of Nature (IUCN) Red List, but breeding numbers are decreasing and may be difficult to monitor. So although our findings suggest the species may recovering quickly, this is just part of a bigger picture for Arctic terns and many other species,” said Dr. Joanne Morten, an ecologist and expert on migratory seabirds at the University of Exeter.