Once-Endangered Peregrine Falcon Is Making a Spectacular Comeback : Wildlife: Their population has soared to 540 after a 15-year effort. But some worry that the recovery effort could face a premature death.

BOSTON —  The peregrine falcon, once reduced to fewer than 100 pairs in the United States, is making a comeback. Now hundreds can be seen swooping off cliffs, ledges and even skyscrapers.

After 15 years and millions of dollars, conservationists say that in a few years, the species will no longer need special protection. They are worried, though, that legislators will decide that the special protection is not needed now.

“It’s progressed marvelously. It’s probably not true that the bird is widely endangered now,” said Jim Enderson, a Colorado College biologist who leads a federal peregrine recovery team.

“It’s been a model program nationally,” said Brad Blodget, Massachusetts’ state ornithologist. “It’s a victory story.”

Enderson estimates that the government could probably change the bird’s classification from endangered to threatened, or even take it off such lists altogether.

This is big news for the peregrine. There were once about 300 pairs in the eastern United States, and many more in the West, but the population was hard hit in the 1950s by DDT and other pesticides. By 1975, there were fewer than 100 pairs were counted in the entire continental United States.

“We were basically starting from zero,” Blodget said.

Groups such as the based Peregrine Fund in Boise, Ida., set about reintroducing the falcon, importing hatchlings from Canada, Scotland, Argentina and other countries.

DDT was banned for nearly all purposes. The federal government earmarked about $300,000 a year for captive falcon breeding, and some states even put check-off options on their tax forms to make it easier for the public to contribute to the cause.

Nationally, the efforts have cost “many millions of dollars,” said Bill Burnham, Peregrine Fund president. The fund spends about $800,000 a year on peregrine recovery.

“It’s a lot cheaper to take care of the environment rather than trying to go in afterward and put them back after you lose them,” he said.

Falcon recovery is not just a simple matter of importing birds from other countries and releasing them here, experts say. Recovery is expensive, partly because mortality rates can be as high as 50% in the bird’s first year, and they are about 15% thereafter, Burnham said.

The fund will release its 3,000th falcon this year, Burnham said.

There are more than 540 falcon pairs in the United States today. There are about 100 pairs in the Grand Canyon, about 90 in California, at least 85 in the Northeast, and about 17 in the Midwest.

“As long as the pesticide situation does not change for the worse, it’s unlikely that this bird is going to be in trouble in the foreseeable future,” Enderson said.

But other conservationists are less sanguine.

“We’re about two-thirds of the way there,” Burnham said. “As far as the release of the peregrines go, there’s probably a need for another six to seven years.”

The birds are still remain scarce in Idaho, where only three pairs have been counted, and in other places. Conservationists say they are keeping their eyes on Washington, hoping Congress does not cut back the program too soon.

“One of the worst things you can do is put a lot of energy into restoration and then stop it,” said Tom French, head of the Massachusetts endangered species program.

The falcons also face a threat from urbanization. Some peregrines have headed for the cities, perching on high-rise buildings. There are nine pairs that swoop and dive among the skyscrapers and bridges of New York City, and a group nesting on a 23-story building in Springfield, Mass., have become stars on a local cable TV show.

But with city life comes hazards such as high wires, airplanes and plate-glass windows. Conservationists worry that these could cripple their breeding efforts.

“Last year, one of the adult males flew over the airport and was hit by an airplane and killed, right in the middle of breeding season,” said Pat Redig, head of the Midwest-based Raptor Center. “I’ve seen those things happen with enough frequency to cause me to be concerned about the fragility of our population.”