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Fossils of flyers: bones tell why Atlantic albatross disappeared.

Two years ago, scientists described 5-million-year-old albatross fossils representing five different species. The fossils, found in North Carolina, raised a question: If albatross once soared above the Atlantic Ocean, why do they now nest only in scattered locations around Antarctica and the northern Pacific?

New fossil data unearthed in Bermuda indicate that the North Atlantic population of short-tailed albatross died off around 400,000 years ago, when an era of global warming caused the oceans to rise, says Storrs L. Olson of the Smithsonian Institution in Washington, D.C.

The fossilized albatross eggs and skeletons, first identified in 1981, represent the only known breeding colony of the birds in the North Atlantic, he notes. Olson and Paul J. Hearty of James Cook University in Townsville, Australia, present their findings in an upcoming Proceedings of the National Academy of Sciences.

"Albatross fossils are pretty rare," comments Steven Emslie of the University of North Carolina at Wilmington. "To find a whole colony preserved like this is incredible."

The fossils formed when a storm sealed off the remains of the colony, Olson and Hearty say. By examining the rocky strata around the fossils, they dated them to the middle of the Pleistocene epoch, almost a half-million years ago.

"The last evidence we had [for Atlantic albatross] was 5 million years ago, and here they are breeding away with eggs and everything only 400,000 years ago," says Olson.

The age of the fossils correlates with one of the warmest periods of the past million years, when ice sheets in Greenland and Antarctica melted and raised the sea level at least 20 meters, the scientists observed.

At that point, says Olson, there would have been very little land left on Bermuda. Moreover, in the high waters, coral reefs no longer could protect the islands and their birds' nests from storms and rough seas.

This was a bad turn of events for albatross, which are notoriously picky about real estate. They roost only on islands that are windy enough for their gliding takeoffs and landings yet are free of mammals that would prey on them and of dense vegetation that could hinder their large wings.

In the Atlantic, where such venues were few, albatross died off, Olson suggests. In the Pacific Ocean, however, there were plenty of suitable islands with higher elevations that would not have been swamped in rising seas.

Although different species can share breeding colonies, fossils of only short-tailed albatross were unearthed at the Bermuda site. This implies that when Bermuda flooded, the other species identified in North Carolina had already disappeared from the Atlantic.

The dating of the Bermuda fossils expands scientists' perspective on short-tailed albatross, "suggesting that the distribution and perhaps total abundance of this species were much broader than previously thought," says seabird ecologist Julia Parrish of the University of Washington in Seattle.

Some short-tailed albatross still nest in Japan, but feather collectors in the early 1900s so decimated the birds' numbers that the species remains endangered today.
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Author:Ramsayer, K.
Publication:Science News
Date:Oct 18, 2003
Words:499
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