A DIMINUTIVE bird that weighs less than a bag of sugar has completed the longest migration on record.

The sooty shearwater travels the Pacific Ocean in a figure-of-eight pattern each year, flying up to 46,000 miles on its migration route.

The distance puts it far ahead of the Arctic tern, which until now was thought to have the longest annual migration, clocking up 22,000 miles between the polar icecaps.

To follow the sooty shearwater (Puffinus griseus) on its migration, scientists fitted 33 birds with electronic tags to record data including position, air temperature and the depth to which they dived in feeding.

A year after the initial capture of the birds in breeding burrows, 20 of the tags were recovered with 19 providing full records of the distances travelled. The data showed that the birds had flown farther on their migration route than any species of animal previously recorded, travelling up to 680 miles a day.

From their breeding burrows in New Zealand, they headed for northern hemisphere feeding grounds off Japan, Alaska or California, some of them stopping off on the western coast of South America.

“These extraordinary migration routes represent the longest recorded of any animal tracked to date,” the international team of researchers reported in Proceedings of the National Academy of Sciences.

Dr Scott Shaffer, of the University of California and one of the research team, said: “The only other bird species known that could rival the migrations of the sooty shearwater would be the Arctic tern. But we don’t know if they do that in a single season, because nobody’s ever tracked them.”

Data showed that the birds dived to a depth of 46ft, on average, to catch fish, squid and krill, and could dive as deep as 225ft. “When they cross the Equator, they’re travelling fast and not stopping much to feed. They feed near Antarctica during the austral summer, then zip north to feed in one of three areas of the North Pacific, taking advantage of high productivity throughout the year,” Dr Shaffer said.

Contrary to previous assumptions, the birds visit just one of their three northern hemisphere feeding grounds before returning south. Researchers were also surprised to discover that once breeding pairs had reared their young, they had taken separate journeys.

Sooty shearwaters are also found in the Atlantic Ocean and visit Britain’s coastal regions. The Atlantic population breeds on the Falkland Islands and Tierra del Fuego. They are one of the most abundant bird species in the world, with a total population of about 20 million, but are classified as “near threatened” because their numbers have been declining.

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