Falcon breeding successes pose a threat to some other birds


May 07, 1991|By Frank D. Roylance | Frank D. Roylance,Evening Sun Staff

Endangered peregrine falcons, like those now raising a new brood of young on the 33rd-floor ledge of the USF&G building in Baltimore, have been so successful they now may pose a threat to some other endangered birds.

"In the mid-Atlantic region, there are probably more peregrines than there ever were," said John Barber, a USF&G employee and former Smithsonian Institution ornithologist.

Peregrines nesting on special towers erected on Assateague and Chincoteague islands on the Eastern Shore have become a particular problem.

The falcons are preying on endangered least plovers and piping plovers on Maryland's Assateague Island, Barber said.

"The solution, I think, is to . . . relocate the peregrines by taking down the towers they're nesting on, and that's very controversial," he said.

Another problem, he said, is that peregrines are aggressive and highly territorial. When Greenland peregrines migrate down the coast, "they're getting beaten up by the East Coast peregrines we have."

Baltimore's peregrines, at least, are innocent of such predation.

Their menu includes a rich diet of mourning doves, flickers, blue jays, robins, an occasional finch and other species plucked from the skies over the city.

"This past weekend [Blythe] did bring in a mallard," Barber said. The city's gradual cleanup and restoration of wetlands along Middle Branch Park is attracting more shore birds to the downtown area, and providing the falcons with ready access to a diet cleaner and more varied than the pigeons that once sustained them.

Their hunting activity is up sharply these days since the hatching 2 1/2 weeks ago of four new chicks, or eyases.

The fat, fluffy white eyases sprawled drowsily in the sunshine on the gravel "scrape" today during their official debut. Father Beauregard was away hunting for lunch, while mother Blythe guarded the aerie against red tailed hawks and curious reporters on the other side of the window glass.

The new eyases bring to 44 the number hatched on the ledge since Beauregard and Blythe paired up in 1984.

The eyases face three more months on the windy ledge before their parents chase them away to search out their own nesting sites and mates.

Until then, Barber said, the adult birds will be busy "shopping" the skies over Baltimore to meet the eyases' feeding schedule of eight or nine meals a day.

Though peregrines are still listed as endangered, their population in the East has "skyrocketed" since the pesticide DDT was outlawed in 1972, Barber said. The pesticide caused a thinning of the birds' eggshells by up to 20 percent, leading to reproductive failures.

Barber said annual tests on Blythe's eggshells show they are now "only 2 percent thinner than the pre-DDT standards," a thinning he called "negligible."

Ninety pairs are known to be nesting east of the Mississippi, where several hundred pairs probably lived and hunted 150 years ago.

Since being reintroduced in the 1970s, peregrines have multiplied and nested on skyscrapers in many cities, and on bridges like the Key Bridge in Baltimore, the Chesapeake Bay Bridge and the Verrazano Narrows Bridge in New York.

They also are returning to their historic aeries on cliffs in New York and Pennsylvania. They are visiting traditional rural nesting sites in Maryland, Barber said, but none has yet nested there.

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