The longest migration in the world is made by the Arctic Tern, a marine bird that lives between the Arctic and Antarctic. An international team of researchers has calculated the duration of its migration. The latter reaches more than 43.500 miles a year (70,000 kilometers). This bird, with a featherweight of 100 grams, can travel during its life the equivalent of 100 return trips between Beijing and Washington. Photo credit: Kiril Dobrev