The bald eagle is one of the largest birds of prey found in North America. It is the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the white-tailed eagle. Its range includes most of Canada and Alaska, all of the contiguous United States, and northern Mexico. Bald eagles typically can be found near large bodies of open water with an abundant food supply and old-growth trees for nesting. In Channel Islands National Park, due to the persecution by humans and the effects of organochlorine chemicals such as DDT, breeding bald eagles were eliminated by the mid-1950's. In an innovative reintroduction program conducted 2002 and 2006, sixty-one young bald eagles were released on the northern Channel Islands.
Quick and Cool Facts
- The scientific name means "a white-headed sea eagle" and comes from the Greek words halos, meaning sea; aetos meaning an eagle; leukos meaning white; and kephalus referring to the head. Bald is from the Middle English word balled, meaning shining white.
- Rather than do their own fishing, bald eagles often go after other creatures' catches. A bald eagle will harass a hunting osprey until the smaller raptor drops its prey in midair, where the eagle swoops it up.
- Had Benjamin Franklin prevailed, America's emblem might have been the wild turkey not the bald eagle.
- The largest bald eagle nest on record, in St. Petersburg, Florida, was 10 feet in diameter and 20 feet tall. Another famous nest—in Vermilion,Ohio—was shaped like a wine glass and weighed over 2 tons. It was used for 34 years until the tree blew down.
- Immature bald eagles spend the first four years of their lives in nomadic exploration of vast territories and can fly hundreds of miles per day. Some young birds from California have reached Alaska.
- Bald eagles can live a long time, with a longevity record of 28 years in the wild and 36 years in captivity.
- Bald eagles occasionally hunt cooperatively, with one individual flushing prey towards another.
The plumage of an adult bald eagle is evenly brown with a white head and tail. The tail is moderately long and slightly wedge-shaped. Males and females are identical in plumage coloration, but reversed sexual dimorphism, which occurs in many raptors, is evident in the species in that females are 25 percent larger than males. The beak, feet, and irises are bright yellow. The legs are feather-free, and the toes are short and powerful with large talons. The highly developed talon of the hind toe is used to pierce the vital areas of prey while it is held immobile by the front toes. The beak is large and hooked, with a yellow cere.
The bald eagle's natural range covers most of North America, including most of Canada, all of the continental United States, and northern Mexico. It is the only sea eagle endemic to North America. At minimum population, in the 1950s, it was largely restricted to Alaska, the Aleutian Islands, northern and eastern Canada, and Florida. It presently occupies historical habitats from the bayous of Louisiana to the Sonoran Desert and the eastern deciduous forests of Quebec and New England. Northern eagles are migratory,while southern birds are resident, remaining on their breeding territory all year.
Historical records indicate that in the early 20th century bald eagles bred on all islands within the park, with at least two dozen nesting pairs over the 8 Channel Islands. Breeding bald eagles provided important ecosystem functions in the northern Channel Islands. For example, bald eagles were once the top marine aerial predator and probably fed upon a variety of seabirds and fish. Bald eagles are generally highly territorial, and in the past this behavior may have prevented golden eagles from colonizing the islands. Due to the persecution by humans and the effects of organochlorine chemicals such as DDT, breeding bald eagles were eliminated by the mid-1950's. In an innovative reintroduction program conducted 2002 and 2006, sixty-one young bald eagles were released on the northern Channel Islands. Bald eagles have also been reintroduced on Santa Catalina Island
The bald eagle explores sea coasts and other large bodies of open water with an abundance of fish as well as rivers,large lakes, and mountainous open country. The bald eagle prefers old-growth and mature stands of coniferous or hardwood trees for perching, roosting, and nesting. Selected trees must have good visibility, an open structure, and proximity to prey, but the height or species of tree is not as being in close proximity to water. The bald eagle is extremely sensitive to human activity, and is found most commonly in areas free of human disturbance.
The bald eagle's diet is opportunistic and varied, but most feed mainly on fish. When fish sources are unavailable, eagles may rely largely on carrion, especially in winter, and they will scavenge carcasses up to the size of whales, though it seems that carcasses of hoofed animals and large fish are preferred. They also may sometimes feed on subsistence scavenged or stolen from campsites and picnics, as well as garbage dumps. Mammalian prey includes rabbits, hares, raccoons, muskrats, beavers, and deer fawns. Preferred avian prey includes grebes, alcids, ducks, gulls, coots, egrets, and geese. Most live prey are quite a bit smaller than the eagle, but predatory attacks on large birds such as the great blue heron and even swans have been recorded. Reptiles, amphibians and crustaceans (especially crabs) are preyed on when available.
Fishing is a learned behavior for the bald eagle, and so juvenile eagles spend their first year eating carrion (carcasses) until they become proficient at fishing (Dooley et al. 2005). Prey remains from bald eagle nests on Santa Catalina Island contained almost 90% fish (Newsome etal. 2010), but an historic bald eagle nest on San Miguel contained more bird remains than fish (Collins et al. 2005). The abundance of seabirds and pinnipeds on the northern Channel Islands means eagles likely take advantage of those resources more than in other areas. This could pose a problem for recovery of bald eagles on the northern Channel Islands (see below), because pinnipeds and seabirds contain more DDE than do marine fish, due to bioaccumulation at higher trophic levels.
Bald eagles nest in trees except in regions where only cliff face sor ground sites are available. They tend to use tall, sturdy conifers that protrude above the forest canopy, providing easy flight access and good visibility. In southern parts of their range, bald eagles may nest in deciduous trees, mangroves, and cactus. It's unknown whether the male or the female takes the lead in selecting a nest site. Nests are typically built near the trunk, high up in the tree but below the crown.
On the Channel Islands, where large trees are scarce, bald eagles have built nests on cliff faces, rock shelves and shallow cliffs, as well as in island pines and Torrey pines. One pair even attempted nesting in a grassland on Santa Cruz Island.
Bald eagles build some of the largest of all bird nests—typically5 to 6 feet in diameter and 2 to 4 feet tall and ranging in shape from cylindrical to conical to flat, depending on the supporting tree. Both sexes bring materials to the nest, but the female does most of the placement. They weave together sticks and fill in the cracks with softer material such as grass, moss, or cornstalks. The inside of the nest is lined first with lichen or other fine woody material, then with downy feathers and sometimes sprigs of greenery. Ground nests are built of whatever's available, such as kelp and driftwood near coastal shorelines. Nests can take up to three months to build, and may be reused (and added to) year after year. The female lays one to three eggs with a usual clutch size of two eggs. The eggs are incubated for approximately 35 days, and the young eagles fledge 10 - 12 weeks after hatching. Bald eagles become sexually mature at five to six years with maturity usually corresponding to when their head and tail feathers become white.
The bald eagle's recovery is a spectacular conservation success story. Once abundant in North America, the species became rare in the mid-to-late 1900s—the victim of trapping, shooting, and poisoning as well as pesticide-caused reproductive failures. In 1978 the bird was listed for protection under the Endangered Species Act. Since 1980, gentler treatment by humans along with the banning of DDT (the bird's main pesticide threat) has led to a dramatic resurgence. By the late 1990s, breeding populations of bald eagles could be found throughout most of North America.
In 2002, with funding from the Montrose Trustees Restoration Program, the park (in conjunction with partner, Institute for Wildlife Studies) began to introduce juvenile bald eagles to the northern Channel Islands. This was done using a technique called "hacking". Birds of approximately 8 weeks of age were kept in one of two hack towers on Santa Cruz Island until they were ready to fly (at approximately 3 months of age). Sixty-one young bald eagles were introduced to the northern Channel Island between 2002 and 2006.
Today, bald eagles are again an important part of the island ecosystem. 2006 marked the first successful bald eagle nest on the Channel Islands in over 50 years, and since that time, the recovering bald eagle population on the islands has grown. As of 2013 there were five breeding pairs on Santa Cruz Island, two on Santa Rosa, and one on Anacapa, and a total of over 40 bald eagles on the northern Channel Islands.
Recovery of bald eagles on the northern Channel Islands was seen as critical to recovery of the endangered island fox, since nesting bald eagles might dissuade dispersing golden eagles (Aquila chrysaetos) from establishing breeding territories on the islands (Coonan et al. 2010). Golden eagle predation was responsible for the massive decline of island foxes on the northern Channel Islands in the 1990s.
In June 2007, the bird's recovery prompted its removal from the Endangered Species list. Continuing threats to bald eagle populations include lead poisoning from ammunition in hunter-shot prey, collisions with motor vehicles and stationary structures, and development-related destruction of shoreline nesting, perching, roosting and foraging habitats.
Based upon information of population trends, the IUCN Red List of Threatened Species has listed the bald eagle a species of Least Concern and current data demonstrates that the population is presently increasing.
- National Audubon Society
- BirdLife International
- All About Birds
- The ICUN Red List of Threatened Species
- The Peregrine Fund
- Coonan, T.J., C.A. Schwemm and D.K. Garcelon. 2010. Decline and recovery of the island fox: a case study for population recovery. Cambridge University Prfess, UK.
- Dooley, J.A., P. B.Sharpe and D.K. Garcelon. 2005. Movements, foraging and survival of bald eagles reintroduced on the northern Channel Islands, California. Pp. 313-321 in Garcelon, D.K. and C.A. Schwemm, eds., Proceedings of the Sixth California Islands Symposium. National Park Service Technical Publication CHIS-05-01. Institute for Wildlife Studies, Arcata, California.
- Collins, P.W., D.A. Guthrie, T.C. Rick and J.E. Erlandson. 2005. Analysis of prey remains excavated from an histoirc bald eagle nest on San Miguel Island, California. Pp. 103-120 in Garcelon, D.K. and C.A. Schwemm, eds., Proceedings of the Sixth California Islands Symposium. National Park Service Technical Publication CHIS-05-01. Institute for Wildlife Studies, Arcata, California.
- Newsome, S.D., P.W. Collins, T.C. Rick, D.A. Guthrie, J.E. Erlandson and M.L. Fogel. 2010. Pleistocene to historic shifts in bald eagle diets on the Channel Islands, California. Proceedings of the National Academy of Sciences 107(20):9246-51.
- Sharpe, P. B. 2012. Bald eagle Restoration on the California Channel Islands, January -December 2011, 10th Annual Report.