Seabirds take record summer vacations.

Seabirds called sooty shearwaters fly some 64,000 kilometers traveling to and from their New Zealand breeding grounds each year, an international research team reports.

That's the longest breeding-season-to-breeding-season trek monitored so far, say Scott A. Shaffer of the University of California, Santa Cruz and his colleagues in an upcoming Proceedings of the National Academy of Sciences.

Biologists have known that several million sooty shearwaters (Puffinus griseus) raise chicks in burrows on little South Pacific islands. The species is being tracked as part of a research program called Tagging of Pacific Pelagics, which follows 23 ocean species, including birds, sharks, and squid.

Three years ago, Shaffer and the shearwater team fit birds with electronic devices that store dive depths, ambient temperatures, and daily locations. But when the researchers returned to New Zealand the next season to collect the tags, they discovered that all of them had fallen off.

In early 2005, the researchers tried again, deploying 33 tags with newly designed holders. At year's end--New Zealand's spring and the start of the sooty shearwaters' breeding time--Shaffer and his colleagues found 19 tagged birds and collected the data.

The devices revealed that the birds that year had flown roughly east from New Zealand and then headed northwest. The birds' round-trip routes described big figure eights, some extending to feeding grounds as far north as Alaska. When the birds crossed the food-poor waters at the equator, they sped up, averaging 910 km a day. Their flight pattern put them over food-rich waters in prime season for both the Northern and Southern Hemispheres. "They're almost in an endless summer," says Shatter.--S.M.