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Ancient diets of Australian birds point to big ecosystem changes

A shifting diet of two flightless birds inhabiting Australia tens of thousands of years ago is the best evidence yet that early humans may have altered the continent's interior with fire, changing it from a mosaic of trees, shrubs and grasses to the desert scrub evident today, according to a University of Colorado at Boulder-led team.

The unprecedented ecosystem disruption is now thought to have led to the extinction of Australia's large terrestrial mammals, which disappeared shortly after humans colonized the continent about 50,000 years ago, said Professor Gifford Miller of CU-Boulder's Institute of Arctic and Alpine Research. Scientists have shown there were no significant swings in the continent's climate during that period, leading most to believe that humans had a hand in the extinctions through over-hunting, spreading disease or by altering the vegetation of the vast interior through systematic burning.

Using isotopic studies of fossil eggshells from both indigenous emus and the extinct, ostrich-sized Genyornis, a new study by Miller and colleagues publishing in the July 8 issue of Science magazine shows that the ecosystem's flora changed swiftly and dramatically after humans arrived.

The analyses, which scientists used to pinpoint particular plant groups ingested by the birds, indicated that emus living before 50,000 years ago preferred nutritious grasses characteristic of milder temperatures and warm summer rains, Miller said. After 45,000 years ago, the eggshell evidence showed emus successfully switched to a diet of mostly shrubs and trees characteristic of drier conditions, he said.

But according to the research team, Genyornis -- which also preferred the nutritious grass prior to 50,000 years ago -- failed to make the dietary switch and became extinct shortly after humans arrived, he said.

"The opportunistic feeders adapted and the picky eaters went extinct," said Miller. "The most parsimonious explana
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7-Jul-2005


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