A team of scientists flying over the Baltimore area in an observation aircraft last month spotted an unusual sight: a pair of bald eagles nesting in a park outside that industrial city, the first such sighting in half a century.

The discovery by scientists from the Maryland Department of Natural Resources marked the first sign that the endangered birds have returned to suburban Baltimore County, where they were last reported in 1936, and a further indication that bald eagles are making a comeback.

"It's very encouraging not only for the bald eagles but the endangered species movement across the nation," said Glenn Therres, a Department of Natural Resources biologist. "The eagle has been a symbol for all endangered species, and it shows that our efforts are paying off."

The two bald eagles were sighted nesting in a wooded area of Gunpowder Falls State Park, a few miles northeast of Baltimore city. The eagles appear to be successfully raising their young within three miles of suburban homes and major roadways, scientists said.

"It is unlikely that the eagles will come in any closer to Baltimore city because of the lack of trees and feeding grounds," said Jackson Abbott, coordinator of the Audubon Naturalist Eagle Survey Project. "It is rare for the {Baltimore} area, but eagles are known to reoccupy old ancestral regions."

The appearance of the eagles, scientists said, is further evidence that despite spreading development and damage from the pesticide DDT, the national bird -- an endangered species since 1973 -- is making a resurgence in the Chesapeake Bay region and across the nation.

In recent years, eagles have nested in several areas near Washington, including Oxon Hill Children's Farm, just outside the District line in Prince George's County. Nests have been reported on an island in the Potomac River near Great Falls Park.

With 83 known pairs of breeding bald eagles, the Chesapeake Bay region contains the fourth largest concentration of the species. The birds in this area are found mainly in Southern Maryland and the Eastern Shore, with 19 pairs reported in Dorchester County, 12 in Charles County and nine in Kent County.

Bald eagles have been sighted in Florida, Maine and Alaska. On Florida's west coast, the birds have nested in some relatively heavily developed areas, scientists said.

According to Maryland officials, a section of Gunpowder Falls State Park, known as the Days Cove area, contains ideal conditions for the eagles: shallow water for feeding, an ample number of trees and protection from human disturbances. Park officials said that the area where the eagles have nested is temporarily restricted to the public.

The population of bald eagles declined drastically during the 1950s and 1960s because of urbanization and the use of pesticides such as DDT. "DDT was banned in 1972, and since then the environment has been ridding itself of the residue of the pesticide in the ecosystem," Therres said.