Basis for Listing

The bald eagle is widespread throughout Canada and portions of the United States, and two races are recognized. The northern race ranges throughout Alaska, most of Canada (except the Archipelago and Hudson Bay lowlands), and across the northern United States from the Pacific Northwest to the Great Lakes and Maine coast. The southern race is found from the Delaware Bay south to Florida and west along the Gulf Coast. Formerly, the bald eagle also ranged across southern California and the southwestern United States. The decline of the bald eagle over its entire range in the contiguous 48 states has been well documented. Environmental contamination by DDT was the primary cause of the decline, and the mechanism was the accumulation of DDT residues in fish, the major food of bald eagles. Since the banning of DDT in the United States in 1972, bald eagle populations have increased nationwide.

In presettlement times, the bald eagle nested throughout Minnesota, including along large prairie rivers and bigger lakes in the southern half of the state. In recognition of the pre-1972 population decline, the bald eagle was listed as threatened in Minnesota when the first state endangered species list was created in 1984. The species had already been added to the federal list of threatened and endangered species in 1978. The Northern States Bald Eagle Recovery Plan established a goal of 300 occupied breeding territories in Minnesota. This goal was surpassed in 1987 when 350 occupied breeding areas were documented. Both the numbers and the range of bald eagles have continued to expand in Minnesota. By 1994, the number of known occupied territories in the states was 615. Consequently, the status of bald eagles under the state endangered species law was changed from threatened to special concern in 1996. Although the majority of bald eagles are found in the forested northern half of the state and along the St. Croix and Lower Mississippi rivers, the species has begun to reoccupy much of its former range in the southern half of Minnesota in recent years. A statewide Known Nest Survey in 2005 located 872 active nests. By combining the results of the Known Nest Survey with data from a survey of random plots, an estimate of 1,312 (+ 220) active nests was derived (Baker and Monstad 2005). Among the 50 states, Minnesota has the third largest bald eagle breeding population, following Alaska and Florida. Data from the 2005 surveys provided support for a U.S. Fish and Wildlife Service proposal to remove the bald eagle from the federal list of threatened and endangered species. The bald eagle was subsequently delisted on August 9, 2007. However, bald eagles and their nests are still protected under the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act.

  Description

The bald eagle is the second largest bird of prey, with a wingspan of 1.7-2.4 m (5.6-7.9 ft.) (Buehler 2000). The white head and tail and contrasting dark brown body of adult bald eagles are diagnostic of this species. Immature and subadult bald eagles are more difficult to identify, as their head and tail are brown or mottled brown and white. Blotchy white coloration on the underside of the wings and tail of young bald eagles help distinguish them from young golden eagles (Aquila chrysaetos), which have a more sharply defined white pattern. Bald eagles attain full adult plumage is their fourth or fifth year. In flight, bald eagles can be confused with turkey vultures (Cathartes aura), but the former can be distinguished by their tendency to soar on flat, board-like wings. Turkey vultures fly with their wings in a v-shape.

  Habitat

Bald eagles select nest sites near lakes and rivers in forested areas where tall, large diameter trees are available for nesting (Grier and Guinn 2003). Nest trees are usually within 0.8 km (.5 mi.) of water. In Minnesota, red pines (Pinus resinosa), white pines (Pinus strobes), large eastern cottonwoods (Populus deltoides), and aspen (Populus spp.) are most often selected for nesting. Eagles have also been known to nest on artificial structures such as powerline poles and osprey (Pandion haliaetus) nest platforms, but this is not common.

  Biology / Life History

Breeding bald eagles defend territories of variable size, averaging 1-2 km² (0.4-0.8 mi.²). The average distance between nests along a shoreline is 0.2-3.1 km (0.1-1.9 mi.) (Buehler 2000). Bald eagle pairs are monogamous and may mate for life. There is evidence that mates may winter together and maintain a pair bond. Each spring, pairs perform spectacular aerial courtship displays. In the cartwheel display, for example, the pair flys to great altitude, locks talons, and tumbles back toward the ground, breaking away at the last moment to avoid collision. Other displays include chases, rolls, and dives from great heights (Buehler 2000).

Nests are built in large, strong trees, often in the supercanopy, that have a view of the surrounding area and provide easy access for the adults. Once built, the nest may be reused and added to in subsequent years. Alternate nest sites are common in many territories. The female lays a clutch of 1-3 eggs, which she incubates immediately, resulting in asynchronous hatching after 35 days. Sibling competition exists among nestlings, with the first to hatch having the advantage. The female generally incubates and broods the young, but both sexes participate in feeding. Young typically leave the nest after 8-14 weeks, although they may become grounded earlier in the event of unsuccessful flight attempts. In most cases, adults will still feed grounded young birds. Immature birds stay with adults for many weeks post-fledging and may be fed by adults up to 6 weeks after leaving the nest (Kussman 1977). Their dependence on adults gradually decreases as the young begin to hunt on their own, until they finally disperse. Although breeding may be attempted at earlier ages with limited success, bald eagles are typically capabable of breeding after 4 or 5 years of age (Buehler 2000).

Not all bald eagles migrate in the fall. Eagles in warm climates, such as Florida, may remain on or near their nesting territories year-round. Bald eagles in cooler climates will migrate if food becomes difficult to find, with adults and juveniles migrating separately. As most bald eagles prefer fish, migration may occur as lakes and rivers freeze over, but the blad eagle is also an opportunistic feeder that forages on fish, bird, and mammal carrion (Buehler 2000).

Bald eagle wintering grounds typically contain open water, ample food, limited human disturbance, and protective roosting sites. Preferred roosts are coniferous or deciduous super-canopy trees. Stopover habitat is similar to wintering habitat, with food supply being the most important factor. Bald eagles migrate alone but may gather by the hundreds at communal feeding sites and roosts. In Minnesota, bald eagles congregate around areas of open water in winter, particularly along the Mississippi River south of Red Wing. Bald eagles return to their breeding territories in late winter, as soon as a food source is available (Buehler 2000). In central Minnesota, bald eagles are typically back at their nest sites by the end of the first week of February.

  Conservation / Management

Human activity is the biggest threat to the bald eagle. Although DDT is no longer a risk factor in the United States, organophosphates, heavy metals, and other pollutants continue to cause sickness or death in bald eagles. Lead poisoning is also a significant cause of mortality, and oil spills threaten eagles in coastal areas. Bald eagles are occasionally still shot or intentionally poisoned. Additionally, collisions with vehicles and power lines are a growing threat as more land is developed (Buehler 2000). Vehicle collisions have also become more frequent as the bald eagle population has increased in Minnesota, due to their habit of feeding on deer carcasses along roads. Land development in wilderness areas and along shorelines destroys breeding habitat and winter roost sites, and increased human activity may cause bald eagles to abandon nesting or winter roosting sites. However, the fact that bald eagles are now successfully nesting in proximity to humans, even in the Twin Cities metropolitan area, indicates that some bald eagles may become habituated to humans if they are not persecuted (Buehler 2000; Grier and Guinn 2003). The U.S. Fish and Wildlife Service has prepared National Bald Eagle Management Guidelines to help landowners, land managers, and others avoid disturbing bald eagles. Preservation of large diameter white pine trees, or other large diameter, tall trees in the vicinity of lakes will ensure continued nesting habitat availability for bald eagles.

  Conservation Efforts in Minnesota

After state listing in 1984, the Minnesota DNR's Nongame Wildlife Program (NWP) prepared management plans for nesting areas to insure that human activities did not interfere with successful nesting. As a result, annual surveys by the NWP documented a steady population increase in the state. NWP staff have also provided technical assistance on a case-by-case when human activities threatened nesting, roosting, or wintering bald eagles, and they have facilitated the capture and transport of injured birds to The Raptor Center at the University of Minnesota. In 2005, the DNR cooperated with the U.S. Fish and Wildlife Service (USFWS) and the U.S. Geological Survey to conduct a scientifically rigorous statewide bald eagle population survey. Another survey led by the USFWS is planned for 2010.

In 2007, after the federal delisting, the USFWS prepared National Bald Eagle Management Guidelines. The guidelines are intended to help landowners, land managers, and others avoid disturbing bald eagles and comply with the intent of the Bald Eagle Protection Act. NWP staff are available to assist the public in applying the federal guidelines to their activities, but any questions regarding interpretation of the guidelines should be directed to the USFWS at (612) 725-3548. Given the recovery of bald eagles in Minnesota, site-specific management plans and annual surveys are no longer being conducted by the DNR.

  References

Baker, R. J., and Y. A. Monstad. 2005. 2005 Minnesota Bald Eagle surveys. Nongame Wildlife Program, Minnesota Department of Natural Resources Report. 4 pp.

Baker, R., J. Galli, and S. Nelson. 2000. 2000 Minnesota Bald Eagle survey. Nongame Wildlife Program, Minnesota Department of Natural Resources Report. 2 pp.

Buehler, D. A. 2000. Bald Eagle (Haliaeetus leucocephalus). Number 506 in A. Poole and F. Gill, editors. The birds of North America. The Birds of North America, Inc., Philadelphia, Pennsylvania.

Grier, J.W. and J.E. Guinn. 2003. Bald eagle habitats and responses to human disturbances in Minnesota. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 48 pp.

Kussman, J. V. 1977. Post-fledging behavior of the northern Bald Eagle, Haliaeetus leucocephalus, in the Chippewa National Forest, Minnesota. Ph.D. Dissertation., University of Minnesota, Minneapolis.