Scientists seriously underestimated the number of birds that people have pushed toward extinction, Pimm, a Duke University ecologist, and his research partners have concluded. On top of that, the frequency of potential bird extinctions is rising sharply, they say.

Over the past 500 years, people have killed, crowded out or otherwise made normal life impossible for close to 500 bird species worldwide, the scientists calculate. During this century, they say, 10 species per year -- of about 10,000 known worldwide -- are likely to meet the same fate.

None of this spells the end of life on Earth. But it's one more clue to the rate at which expanding human populations threaten wildlife. It comes not long after a United Nations report warned against a coming wave of plant and animal extinctions unmatched since dinosaurs were wiped out 65 million years ago.

"We will survive. But the world will change. The question is, will it be the sort of world that you and I would want to live in?" said Pimm, one of five researchers who published the revised extinction estimates in the Proceedings of the National Academy this summer.

Bird extinctions are nothing new. North Carolinians alive today have never seen a Carolina parakeet, the only known parrot native to lands north of Mexico. Nor have they glimpsed the passenger pigeon flocks that were big enough to block views of the sky when Europeans reached North America. Hunting and forest destruction obliterated both by 1920.

Such losses can to traced to more than European settlement of a "New World." People have eliminated bird species worldwide for a very long time.

Pimm and colleagues point to the toll from Polynesian exploration and settlement of Pacific Ocean islands. Although no one documented those losses in scientific log books, fossils dug in recent history tell the story. Likewise, fossil remains found in recent years have linked bird extinctions to human intrusion in places such as Madagascar.

The fossils, along with evidence that many birds today would not survive without human help, must bump up long-accepted estimates of birds driven to extinction, the scientists say. The old estimate of 154 species pushed to extinction since 1500, or one every four years, should be replaced by close to 500 species, or almost one every year, the scientists say.

And now that the human population is growing so fast -- today's worldwide total of 6.5 billion may reach 9 billion in 50 years -- expected harm to birds will only accelerate, they say.

Early on, island-dwelling birds were the ones threatened most quickly, by hunters' nets, clubs or firearms. The introduction of rats and snakes in some settings did severe damage, too, since birds that evolved without such predators had no defenses against them.

In more recent history, increasing numbers of birds dwelling on continents have been threatened, too. Hunting still takes a toll. But the biggest threat has been habitat destruction, and not just in obvious spots such as tropical rain forests. Human practices that harm food supplies also pose dangers.

Around the world

Ask ornithologists, and they can all rattle off multiple sad stories now being played out, said Cagan Sekercioglu, a Stanford University bird expert and conservation biologist who was one of Pimm's co-authors on the new extinction estimate.

In Europe, the population of the once plentiful skylark, a songbird, has plummeted in recent decades after farmers changed planting and sowing practices. The move from planting grains in the spring to growing them during fall and winter disrupted the birds' feeding.

In India, ubiquitous vultures have nearly disappeared in just over 12 years, poisoned by a drug commonly given to cattle. The vultures' decline has resulted in growing numbers of wild dogs and rats since fewer winged scavengers compete with them for food at dumps. India recently announced it would ban the drug, but biologists are not certain the vultures can bounce back.

In the Americas, the feeding patterns of the red knot, a robin-size bird, are being challenged. The knot migrates 20,000 miles from the southern tip of Patagonia in Chile to the Arctic in Canada to breed. A key stop occurs in Delaware Bay, where the birds show up just as horseshoe crabs climb out of the water to lay eggs. The birds feast on those eggs to fuel up for the rest of trip. Now there's less food, because commercial fishermen use the crabs as bait.

Pimm and his colleagues in the extinction study hope to convey to the public that such losses are part of a global trend.

"We're hoping that one day regular people will consider this unacceptable," said Stanford's Sekercioglu.

People outside academia are paying attention to the researchers' conclusions. Greg Butcher, director of bird conservation for the National Audubon Society, is one.

"The scariest part is that the closer you look at it, the worse it looks. Almost all the errors have been underestimates," Butcher said. "If we are going to reverse the problem, we are going to have to do a whole lot more than we'd thought."