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The nearly extinct peregrine falcon is flying a comeback course. Biologists encourage nesting on roofs, bridges, towers across US

On a blustery 17th-floor ledge of an office building in Boston, two rare peregrine falcon chicks are hopping around clumsily awaiting their next meal. Their adoptive parents can be seen soaring more than a mile above the metropolitan sprawl. On rare occasions they are spotted in a divebomber's tuck chasing after a pigeon or sparrow at more than 200 miles an hour.

The two chirping 14-inch fledglings, still showing a puff of down amid their brown, gray, black, and white plumage, complete the formation of Massachusetts's first family of the endangered peregrines in 36 years.

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The peregrine nearly became extinct in the early 1970s because of excessive use of pesticides. Boston is one of many American cities with programs aimed at regenerating them.

Mark Spreyer, an ornithologist and director of the Chicago Peregrine Release Program, says ``the success of [restoration of] the peregrine largely depends on its willingness to adapt.... The [nearly extinct California] condor, for example, is less adaptable.''

Proof of its adaptability can be seen in more than a decade of successful releases from bridges in New York and Maryland, towers in New Jersey and Illinois, cliffs in Vermont, Utah, and California, and rooftops, as in Boston.

This city's new peregrine family is the result of an elaborate plan involving egg swapping, dummy eggs, laboratory incubation, and ``hacking'' (hand-raising and releasing). Thomas French, director of the Natural Heritage and Endangered Species Program of Massachusetts, and other state biologists who orchestrated the plan, began hacking peregrines here three years ago.

Ten years ago there were just 12 pairs of peregrines in California, says James Weaver, project manager for the 18-year-old federally funded Peregrine Fund in Ithaca, N.Y. Today there are more than 80 pairs in California and more than 300 pairs nationwide, excluding Alaska, Mr. Weaver says. There are some 60 pairs of falcons in the East, where there were none in 1975, he adds.

``The sale of DDT was banned [in 1972] but not its manufacture,'' says Tanner Girard, president of the Illinois Sierra Club. ``Even though we've eliminated the [pesticide] problem in our country, you have to take a more international approach'' to restoring peregrines, Dr. Girard says.

American and European chemical manufacturers sell pesticides to Latin American countries where birds like the starling and sparrow - a peregrine staple - winter. Being at the top of the food chain, the peregrine preys on contaminated birds and is still dangerously affected by DDT.

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Early last month the Peregrine Fund released its 2,000th falcon. Weaver concedes that the success of peregrine rehabilitation will rely heavily on the efforts of man and governments.

When new falcons are released, they are often equipped with radio transmitters enabling biologists like Walter C. Crawford, director of Raptor Rehabilitation and Propagation Project Inc., to follow their flights. Dr. Crawford's St. Louis-based study center works with 28 species of raptors - or birds of prey - and has recently released seven peregrines in the St. Louis area.

Pesticides such as DDT are known to cause raptors to lay eggs with shells too thin to support the parents' weight. But Crawford cites several other reasons that have added to the decline of the peregrine in the Midwest, such as:

The extinction of the passenger pigeon, one of the peregrine's main food sources.

Collection of falcon eggs by hobbyists.

Alteration and tampering with food sources and nesting sites.

Destruction of habitat through development.

Shootings by farmers or irresponsible hunters.

``The decline of the peregrine falcon can be attributed 100 percent to man,'' Crawford says.

Nowadays, peregrines can be monitored more closely than they have been. ``Each adult bird of his seven in St. Louis carries a radio transmitter and is watched from 4:30 in the morning to 10:00 at night - a very, very time-consuming project,'' Crawford says. He tracked one peregrine that strayed to Indianapolis where it paired with a Minnesota-released falcon.

Boston's female peregrine parent drifted from her Toronto release site much as the bird Crawford tracked. Dublin, Boston's male parent or ``tiercel,'' and Shannon, the much larger female or ``falcon,'' are the first of the 12 peregrines released so far in Boston successfully to raise chicks, or ``eyas,'' as young falcons are called.

They produced a clutch of four eggs in early May, but all four were crushed as a result of inexperience by the birds in choosing a nesting site, Dr. French says. Fourteen days later, the pair produced four more eggs.

``It was clear,'' French says, ``that without some form of active management, we would stand the chance of losing the second clutch of eggs as well.'' The eggs were then swapped with dummy eggs and sent to an incubation laboratory at Cornell University. When hatching time came 28 days later, a prairie falcon chick was placed in the Boston nest, and Dublin and Shannon accepted it immediately.

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