Bald Eagle Facts
- Facts and Figures
- Bald Eagle Nests
- Food Habits
- Causes of Mortality
- Bald Eagles and DDT
- Conservation and Management
The bald eagle has been our national symbol since 1782, when Congress adopted the design for the Great Seal of the United States. Ranging from Alaska to the northern border of Mexico, and from the Pacific to the Atlantic coast, the bald eagle is the only eagle found exclusively on the North American continent. Long a key symbol in Native American cultures, the bald eagle has more recently been emblematic of freedom and democracy as well as wilderness and the environmental ethic.
Facts and Figures
The bald eagle is not really bald. "Bald" is from an obsolete English word meaning white. Bald eagles do not attain their white head and tail feathers until their 5th year of age. Immature birds undergo progressive annual changes in plumage pattern from uniformly dark brown their first year to extensive white and brown mottling in their fourth year. Other notable characteristics include a large downward-curving yellow bill, and yellow feet with sharp talons for catching prey.
- Size: Size increases with latitude; Alaskan birds are noticeably larger.
- Weight: Males 7-10 pounds, Females up to 14 pounds
- Wingspan: Males greater than 6 feet Females up to 8 feet
- Age (record longevity): 28 years in wild, 36 years in captivity
Capable of breeding in fifth year of life when adult plumage attained. Pairs mate for life. In the Chesapeake Bay area, breeding activity begins in November and can last through mid- July. Most eggs laid mid-January to late February. Females lay 1-3 eggs, 2-egg clutch most common (79%). Incubation period is 35 days. Males participate, but female does most of incubating (72%). Both parents hunt and feed young. Young eaglets fledge in average of three months (8-14 weeks).
Bald Eagle Nests
Both sexes participate in nest building, which usually begins 1-3 months before egg-laying. Generally built in one of the largest live trees available with accessible limbs capable of supporting the nest. Nests built in top quarter of tree just below the crown, against the trunk or in the fork of large branches close to the trunk. Nest constructed from sticks collected on the ground or broken off of trees. Grasses, mosses, and other material may be added as filler. The nest bole is lined with finer woody material and ultimately with downy feathers from adults. Additional materials added throughout the year, including daily additions during breeding season. Nests used for multiple years may reach enormous dimensions. Bald eagle nests are among the largest nests of all birds; Typical size is 5-6 feet in diameter and 3 feet tall! Famous Ohio nest used for 34 years measured almost 9 feet in diameter, close to 12 feet tall, and weighed over 2 tons! Record St. Petersburg, Florida nest was 9.5 feet in diameter and 20 feet tall!
Bald eagles, like other raptors, are birds of prey. They usually seek out aquatic habitats (bays, lakes, large rivers), as fish are their preferred food, but bald eagles are opportunistic foragers.
In addition to fish, they eat a great variety of aquatic and terrestrial mammals, birds, reptiles, and amphibians. They will also feed on carrion, especially in winter, and are known to steal prey from other birds, such as osprey.
Diet of nesting bald eagles (summary of 20 studies):
Northern (breeding north of 40° N), non-coastal populations including those in Alaska, generally migrate south for the winter between August and January.
Bald eagles in the Great Lakes region and adjacent areas in Canada may migrate eastward to winter along the Atlantic Coast from Maine and New Brunswick to Chesapeake Bay.
Because of its rich food resources, Chesapeake Bay also is host to a large influx of summer migrants from Florida and other Gulf Coast states from May to September.
Most immatures on Chesapeake Bay limit movements to the bay. Less than 10% of radio-tagged individuals moved north in summer.
Northern birds return to breeding grounds as soon as weather and food availability permit, generally January to March.
Causes of Mortality
Most bald eagle mortality is human-related, either directly or indirectly. Of 1,428 individuals examined by the National Wildlife Health Center from 1963 to 1984, death was attributed to following causes:
(impact with wires or vehicles)
Bald Eagles and DDT
Reproduction impaired due to eggshell thinning across lower 48 states during years of DDT use: 1947-1972.
Changes in nest success (percentage of active nests with at least one young fledged) and productivity (number of young fledged/active nest) for Chesapeake Bay:
- Pre-DDT Nest Success: 79%
- 1962 Nest Success: 14%
- Pre-DDT Productivity: 1.6 young fledged/nest
- 1962 Productivity: 0.2 young fledged/nest
- 2005 Productivity: 1.58 young fledged/nest
In lower 48 states, bald eagle populations have shown tremendous growth since DDT banned in 1972:
- 1963: 417 estimated breeding pairs
- 1982: 1,482 estimated breeding pairs
- 1997: 5,000 estimated breeding pairs
- 2005: 7,066 estimated breeding pairs
Conservation and Management
Bald eagles were protected under the Bald Eagle Protection Act in 1940 in Alaska and lower 48 states. The Act prohibited taking or possession of bald eagles or any parts including feathers, eggs, and nests.
Bald eagles were further protected as Endangered Species under 1973 Endangered Species Act, however, expanding populations led to down-listing as a Threatened Species in 1995. In 2007 bald eagles were formally "de-listed" or removed from the federal Endangered Species Act. Bald eagles continued to be listed as a state threatened species by DGIF.
Bald eagle populations have continued to grow in Virginia and across the country. In 2011 the breeding population in Coastal Virginia was more than 730 pairs (more information: Center for Conservation Biology). In addition, DGIF surveys in the Piedmont and Mountain regions of Virginia indicate an increase in nesting in these areas as well. As bald eagle populations near saturation in Coastal Virginia an increasing use of urban and suburban nest locations has been observed. The continued recovery of bald eagle populations in Virginia led the DGIF Board to take action at their August 14th meeting to remove the bald eagle from the Virginia state list of threatened and endangered species effective January 1, 2013. This is a remarkable milestone along an impressive conservation success story. DGIF will continue to work to preserve the gains this species has made.