U.S. scientists say human activities have caused some 500 bird species worldwide to become extinct since the year 1500 and the rate is rising.

The Duke University scientists said the 21st century extinction rates likely will accelerate to approximately 10 additional species per year unless societies take action to reverse the trend. Without the influence of humans, the expected extinction rate for birds would be roughly one species per century, according to Stuart Pimm, a professor at Duke University's Nicholas School of the Environment and Earth Sciences and one of the report's principal authors.

"What our study does, for the first time, is provide a well-justified and careful estimate of how much faster bird species are going extinct now than they did before humans began altering their environments," said Pimm. "Extinction rates for birds are hugely important, because people really care about birds," he said. "People enjoy them, and bird watching is a big industry. So we know the rates of bird extinctions better than the rates for other groups of species."

The report appears in the online edition of the Proceedings of the National Academy of Sciences.

Copyright 2006 by United Press International