Arctic terns can fly more than 80,000 km (49,700 miles) a year, beating past estimates of the seabirds' record migrations and equivalent to three round trips to the Moon over a lifetime, a study showed on January 11.
Tiny tracking devices attached to 11 of the small white birds breeding in Greenland or Iceland showed they flew a far more meandering route than expected on their annual trips to the Antarctic and back, an international team of scientists said.
Already widely reckoned to have the longest migration of any creature, the birds flew an average of 70,900 km in a year, with one clocking up 81,600 km. That was double the 40,000 km often estimated in the past.
And over a tern's lifetime of up to 34 years, the migrations add up to about 2.4 million km - equivalent to three return trips to the Moon or a dizzying 60 times around the Earth.
"This is a mind-boggling achievement for a bird of just over 100 grams," said Carsten Egevang of the Greenland Institute of Natural Resources and lead author of the study with experts in Denmark, the United States, Britain and Iceland.
"Tracking of Arctic terns...reveals longest animal migration," the scientists wrote in the US journal Proceedings of the National Academy of Sciences. Other birds, such as albatrosses or sooty shearwaters, also have massive migrations.
Terns breed around the Arctic, from Iceland to Alaska, and exploit rich summertime fisheries for shrimp-like krill, other plankton and small fish in both polar regions. They escape freezing dark polar winters with their marathon flights.
On the way back north in April and May, the birds took a long "S"-shaped route up the Atlantic, apparently to use prevailing winds to save energy. Flights from Antarctica to Greenland took about 40 days, an average of 520 km a day.
Small "geolocator" devices, weighing 1.4 grams and attached to the tern's leg, recorded the birds' position daily. The data were then downloaded after the birds were caught on return to their Arctic breeding sites.