Bay’s bald eagles making comeback; threats still loom
I saw my first bald eagle more than 20 years ago on a school trip to Blackwater National Wildlife Refuge. Bald eagles were not a common site and I was enthralled with this rare bird. Since then, as bald eagles have made a comeback in the Chesapeake Bay region, I've spotted many of them, especially while canoeing the many creeks and rivers in the watershed.
The adult bald eagle is easily recognized by its brown body, white head and tail, and large, yellow beak and eyes. The scientific name, Haliaeetus leucocephalus, means "white-headed sea eagle." Immature birds are dark brown, mottled with white. The white head and tail begin to appear at 3-4 years of age and is complete by 4-5 years.
Adult males measure about 3 feet from head to tail, weigh 10-12 pounds and have a wingspan of 6-7 feet. Female birds are slightly larger. In flight, the bald eagle has a distinctive, flat-winged profile, unlike the "V" shape of a vulture.
Breeding pairs usually build their nests high in mature loblolly pines, tulip poplars and oaks along the shores of the Bay and its tributaries. Eagle nests tower 80-110 feet above the ground. The massive nests are often used year after year, growing to 6-8 feet in width and averaging 4 feet deep, although some may get as deep as 10 feet. They are built of large sticks and plants with soft, inner lining of broom sedge and pine needles.
Bald eagles usually lay one clutch of one to three eggs in late winter. The eggs hatch after 35 days. The young are covered with soft down but soon grow feathers and are flying within three months. By the fourth month, they are on their own. Like eagles elsewhere, Chesapeake birds feed primarily on fish, but also eat ducks, geese, small mammals, snakes and turtles.
Historical records show that in the early 1900s, more than 1,000 pairs of birds nested around the Bay each year, averaging one pair for every five miles of shoreline. However, just prior to the 1940s, bald eagles began to decline because of the direct killing of birds, loss of habitat and decline of prey. In 1940, the Bald Eagle Protection Act made it illegal to kill, harm, harass or possess bald eagles, alive or dead, including eggs and feathers.
They began to recover but then another culprit entered the picture. Just before World War II, the use of the pesticide DDT to control mosquitoes was widespread in coastal areas. Bald eagles were feeding on prey contaminated with the pesticide. By the late 1960s and early '70s, researchers determined that DDE, a breakdown product of DDT, built up in the tissue of adult female bald eagles. This prevented the calcium release needed to produce strong eggs and caused reproductive failures.
Surveys of the Chesapeake Bay area revealed a drop in active eagle nests and the number of eaglets fledged. In the 1930s, an average of one to two eaglets were produced per nest, but in the early 1960s, the average dropped to one eaglet for every five active nests.
The use of DDT was banned in the United States in 1972, but our nation's symbol was still in trouble. By that time, there were fewer than 90 breeding pairs of eagles in the Chesapeake area.
In 1973, under the Endangered Species Act, bald eagles were listed as endangered throughout the lower 48 states except in Michigan, Minnesota, Wisconsin, Washington and Oregon, where it was listed as threatened.
Since the late 1970s, the amount of DDE found in Bay eagle eggs has dropped and more young eagles have hatched. In 1977, the 40 nests in Virginia and Maryland produced 63 young. Nesting success has steadily increased each year. By 1996, 179 bald eagle nests produced 508 young!
During the past 25 years of recovery, eagles have made a rebound, in part because of the replacement of healthy adult nesting pairs. Bald eagles in the United States have responded to the protection afforded by the Endangered Species Act as well as several other actions. Banning DDT, preventing illegal shootings and protecting habitat through land acquisitions and landowner agreements have all helped to bring back bald eagles.
The Chesapeake Bay now has one of the highest concentrations of bald eagles in the lower 48 states. In addition to the breeding population, the Bay supports winter migrants from as far north as Canada and summer migrants from Florida.
On Aug. 11, 1995, the bald eagle was reclassified from endangered to threatened. Although Chesapeake bald eagles are making a comeback, the population still faces many potential problems.
Industrial, residential and marina development along the shoreline continues to remove nesting areas. New pesticides, which may impact eagles and other wildlife, are continually being produced. There is a continuing need to monitor new chemicals and environmental contaminants.
For bald eagle populations to improve, they need access to adequate habitat, including suitable nesting trees within a mile of open water, isolation from human activity and a stable food supply that includes mostly fish, other birds, mammals, reptiles and amphibians.
Biologists are working so that one day bald eagles in the Chesapeake Bay area will no longer need the protection of a threatened or endangered status. Through habitat protection, identification of important nesting, roosting and feeding sites, and the monitoring of potential contaminants, the bald eagle will continue its journey of recovery.
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