Miniature new transmitters recently revealed that the 4-ounce (113-gram) bird follows zigzagging routes between Greenland and Antarctica each year. In the process, the arctic tern racks up about 44,000 frequent flier miles (71,000 kilometers)—edging out its archrival, the sooty shearwater, by roughly 4,000 miles (6,440 kilometers).

(See map at right: Green represents autumn/southward migration; red denotes winter range; and yellow represents spring/northward journey.)

"There have been all kinds of theories, but now, for the first time, we've been able to show what the birds are doing out there," said the lead author of the study, Carsten Egevang of the Greenland Institute of Natural Resources.

Since the birds often live 30 years or more, the researchers estimate that, over its lifetime, an