Boston — Ten years after passage of the Endangered Species Act, which sought to prevent the extinction of the bald eagle and other North American animals, the bird that symbolizes liberty in the United States appears to be making a comeback.
''The future of the bald eagle is bright,'' says Paul Nickerson of the US Fish and Wildlife Service.
The endangered species biologist says there are an estimated 1,600 to 1,800 pairs of adult bald eagles nesting in the lower 48 states of the US. Of those, about 200 pairs are currently nesting in Northeastern states - compared with about 100 pairs of nesting eagles there a decade ago.
Some experts have estimated that in the late 1960s and early '70s the number of nesting pairs of bald eagles throughout the continental US may have dropped to as low as 400 to 600.
The drop was attributed primarily to the contamination of eagle populations by the pesticide DDT. DDT causes female eagles to lay thin-shelled eggs that are prone to crack prematurely. The pesticide was banned in 1972, but its effects have lingered in eagles. In addition, eagles are not naturally prolific reproducers, experts say. A pair of nesting eagles may produce one young eagle a year.
Biologists and conservationists have been working to restore US eagle populations by incubating fragile eggs in captivity and by relocating eagle chicks from the wilds of Canada and Alaska - where eagles are abundant - to selected sites.
The first relocation project was conducted in New York state in 1976. As a result of that project, bald eagles are now producing young in New York for the first time since 1970, according to the Fish and Wildlife Service. Similar projects are under way in neighboring New Jersey, Pennsylvania, and Massachusetts. Eagles have not been known to have nested in the Bay State for 75 years.
In 1983, a total of 45 young eagles were released in the four states.
The idea is that eagles habitually will return to the area where they first learned to fly when it comes time to mate and build a nest. Biologists feel this is one way to reintroduce eagles to areas where their populations have long since disappeared.
Young eagles (preferably six and a half weeks old) are taken from their parents' nests in Alaska or Canada and moved to man-made 30-foot towers in the new location. The birds are then fed about two pounds of fish a day for several weeks until they are big and strong enough - and have the desire - to fly.
''We feel that nearly half of those birds released will survive and return to breed in the areas where they were released,'' says Mr. Nickerson, who has been working with eagles since 1971.
He estimates that because of such projects and an increased public awareness of the plight of the bald eagle, eagle populations will continue to grow at a rate of 5 percent a year in this country.
Wildlife specialists warn, however, that while the threat of DDT has steadily diminished since the 1972 ban, eagles continue to face other significant threats.
Among them are the continued destruction of the eagle's natural habitat through land clearing and development. Eagles prefer to nest in trees about 50 feet off the ground, and near large lakes or reservoirs. The primary nesting areas of bald eagles are in Maine, Florida, the Chesapeake Bay region, the Great Lakes area, and the Pacific Northwest. In the course of a year, however, eagles frequent each of the contiguous 48 states.
The Washington-based National Wildlife Federation has identified 450 specific areas in the lower 48 states as important wintering grounds for bald eagles. The areas have been identified in an effort to prevent further habitat destruction.
''It's a matter now of how well we can develop bald eagle habitats,'' says Brian Millsap, raptor biologist with the National Wildlife Federation.
Eagles also face a variety of other threats, according to biologists. They include: lead poisoning as a result of eating ducks that have ingested lead shot used by duck hunters; electrocution from perching on uninsulated power lines; poisoning from eating rodents that have eaten rodent bait; and being shot by ''vandals with weapons.''
In 1982, 17 eagles are known to have been shot and killed in the US. Nickerson said many of the shootings occur because people aren't aware that bald eagles do not attain their distinctive white head and tail feathers until they reach maturity at four or five years old.
Not all shootings are accidental. Last June, federal and state authorities broke up an eight-state ring based in South Dakota dealing in eagle feathers, bones, beaks, and talons. An estimated 200 to 300 eagles were reported to have been killed during a three-year period.