SPRINGFIELD, Mass. – One of the most visible successes of the Endangered Species Act, peregrine falcons, are thriving once again on the Northeast’s wild mountain cliffs and have found new hunting grounds among its urban skyscrapers.

Last week, the U.S. Fish and Wildlife Service approved a 15-year monitoring program for the world’s fastest birds, which were removed from the federal endangered species list in 1999.

“This is our first real opportunity to not only recover a species, but show we can live up to our responsibilities to ensure that once the protections are removed the species remains stable and continues to increase,” said Michael Amaral, a biologist with the service’s regional office in Hadley.

Spectacular fliers that can power-dive on their prey at speeds up to 200 mph, the peregrine falcons had been barely holding on in a few western areas. By 1970, there were only 39 known nesting pairs in the lower 48 states. The decline was blamed on pesticides, primarily DDT, that were linked to severe thinning of the birds’ eggshells.

After DDT was banned in 1972, the falcons began to recover. And captive-raised birds were reintroduced to the East, where they had been absent for generations.

“We started from zero in 1960,” Amaral said.

Today, there are about 2,000 nesting pairs nationwide and 125 in New York and New England. This year, for the second time, the New York and New England birds successfully raised more than 200 chicks, he said.

Despite the lifting of the federal designation, peregrine falcons remain on state endangered species lists in the Northeast. Vermont, which now has 29 nesting pairs, is considering relaxing its designation to threatened.

The state designations mean that all the nests in the region will continue to be checked annually although the federal plan calls for samples at three-year intervals, Amaral said. Among things biologists will track is potential problems with chemicals and effects of diseases such as the West Nile virus.

So far, the northeastern birds appear largely unaffected by West Nile, although this year one adult bird was killed by the virus in Virginia, he said.

In northern New England, most of the peregrines have tended to settle on wild cliffs. All but one of the Vermont pairs are tucked into the crags of the Green Mountains.

At Acadia National Park in Maine, dozens of people participate in “Hawkwatch” every fall, when peregrine falcon chicks leave their nests and join the flight south for the winter.

In southern New England, the fierce hunters with a taste for pigeon were attracted first to the man-made cliffs of tall city buildings.

The first native Massachusetts chicks of the restoration effort were hatched in Boston in 1987. Then a wild pair settled on a 21st-floor ledge of a downtown office building in Springfield in 1989. This year the state had 10 nests, with eight on buildings and bridges in Boston, Springfield, Fall River, Lawrence and Amherst and two on cliffs in Erving and Sunderland.

Banded Massachusetts peregrines have shown up from southern Ontario to New Jersey. One Boston-hatched bird is nesting on an Atlantic City, N.J., casino while others are nesting on New York City’s Throgs Neck and Verrazano bridges.

Four out of the five Connecticut nests are on buildings and bridges and so are both Rhode Island nests.

The move to the cities has introduced thousands of urban residents to the rare birds and bird watching. Several falcon pairs are on the Internet with Webcams, and one downtown nest has been monitored for years on cable television in Springfield, where the minor league hockey team is now called the Falcons.

“It’s a chance to see nature up close and personal and surprisingly popular,” said Douglas Guthrie, general manager for Comcast, Springfield’s cable television outlet. “The feedings always make for good television. And whenever a chick totters close to the ledge, the phones start ringing.”

The show, on screen and off, hasn’t lacked for sex or violence. A few years ago, a ruthless young female peregrine tried to move in on the Springfield couple. Downtown office workers watched enthralled as the two female birds battled high above the city streets sometimes plummeting for hundreds of feet through the sky with talons locked. And the male quietly sat on the eggs.

New York, where biologists Heinz Meng at the State University of New York at New Paltz and Tom Cade at Cornell University launched the nation’s first captive breeding and release program in the early 1970s, now boasts the most nesting pairs in the East with 49.

New York City alone has at least 15 pairs on city bridges and buildings. Others are found in the wild cliffs of the Adirondacks, Shawangunks and Catskills and the rocky Hudson River palisades, Amaral said.

“It’s good to have both, because the city birds typically are in nest boxes or under bridges where they are really protected,” he said. “And they have a very stable food supply with pigeons and mourning doves.”

“The cliff nesters are more susceptible to weather and to fluctuations in food supply,” he said.

“Now it’s a species that’s very available to the American public,” he said. “The average person has a lot of choices to see a peregrine falcon from downtown Springfield to a remote cliff in the Adirondacks or White Mountains.”