DESCRIPTION: The bald eagle, our national symbol, is a member of the hawk family. Adults are unmistakable large raptors (total length 0.9 meter; wingspan, about 2.1 meters; females distinctly larger than males) with a white head and tail, blackish to dark brown body and wings, and yellow eyes, bill and feet. Juveniles are uniformly brown with scattered white feathers. By their fourth year, most immatures acquire a plumage pattern that approximates the adult, but commonly they still have dusky mottlings on the nape and several brownish feathers in the tail. Traces of immature plumage are retained as late as the 6th year.
HABITAT AND DISTRIBUTION: Bald eagles occur primarily in riparian or estuarine habitats, which are associated with coasts, rivers, lakes, and marshes. In Florida, nearly all nests are within 0.6km of a body of water (even those in the state's interior) where the birds can hunt. Outside the nesting season they are not as closely limited to shores, both adults and immatures tending to gather where food is most easily available. Florida's nesting bald eagle population of more than 600 pairs (of which 25 pairs have been identified in Collier County) constitutes over 80 percent of the entire population within the southeastern United States. In fact, Florida has more eagles than any individual state except Alaska. Bald eagles are separated into "northern" and "southern" populations, with the former nesting mostly in the northern United States, including Alaska, and Canada. The southern population occurs roughly from southern California eastward through the Southwest and Southeast, then northward along the Atlantic Coast to Chesapeake Bay area. The northern population is much more numerous in Washington, Oregon, Minnesota, Wisconsin and Michigan. The southern population is sparsely distributed except in Florida. Most of Florida's nesting bald eagles occur in the peninsula. Major concentrations of nests are found along the St. Johns River, in the Alachula/Marion counties area, in the Osceola/Polk counties area and through the southwestern coastal counties from Tampa Bay southward to Collier County.
LIFE HISTORY AND ECOLOGY: Most nests are in the tops of tall living or dead trees (pine or cypress in most areas, occasional mangroves along the southwest coast). Nesting requirements also include a clear flight path to the nest, with an open, unobstructed view of the surrounding area, as well as the proximity of good perching or roosting trees. Unlike ospreys, they are apparently reluctant to nest on man-made structures. Typical nests are flat-topped heaps of dead sticks lined with finer material (grass, Spanish moss, pine needles, seaweed, green leaves) that may be used for years with new material added annually. Eagles may have more than one nest within their territories. Eagles also may commandeer the nests of other large birds, particularly ospreys. Nests and nesting trees may be lost due to fire, lightning, and storms; nests may be taken over by great horned owls. Bald eagles mate for life and use the same nesting territory year after year. In Florida, established pairs begin to repair nests in nearly fall and eggs may be laid as early as late October. Females may lay another set of eggs, if the first is lost, and thus active nests with eggs may occur as late as February or, rarely March. The usual clutch is 2 eggs, but sets of 3 are not uncommon, and sets of 1 and 4 reportedly occur. The incubation period is about 35 days. The eggs are very small for the size of the bird and the young are helpless when they hatch and spend 11 to 12 weeks in the nest before fledging. Both parents participate in incubation and care of the nestlings, but details of the division of labor vary considerably between pairs. Aggression between nestlings is common and causes substantial mortality of small young. During the first summer, the young birds typically wander northward, some as far as Canada, but return by adulthood at 4 or 5 years of age. They then find a mates and initiate breeding, most commonly in the vicinity of where they were originally hatched.
Bald eagles are opportunistic feeders, taking a variety of vertebrate prey, both live and carrion (including roadkill). In Florida, fish comprise most of their diet. Other components of their diet include aquatic birds and turtles, and to a lesser extent snakes and small mammals. Eagles are particularly known for stealing food from ospreys with whom they share waterfront habitats, but they will steal from many kinds, especially other eagles.
BASIS OF STATUS CLASSIFICATION: Historically, population numbers have declined, with the most severe population reduction in the interior United States. Prior to the European settlement of Florida, it was estimated that 1,000 pairs of eagles nested throughout Florida. Florida's population is now one-half to two-thirds of what it was at the end of World War II.
In the years following World War II, a sharp decline in eagle population numbers was observed. In the late 1940's, a decline in nesting was observed in Florida. Biologists attributed this decline to DDT. This pesticide, used extensively for mosquito control after the war, was being washed into waterways and being built up in fish tissues through biological magnification in the food chain. The result of the eagles' ingestion of this contaminated prey was a drastic decline in eagle reproductive success and hence population numbers. These reductions in productivity were seen from all populations in the contiguous United States. Since the ban of DDT and other pesticides (such as dieldrin and endrin) usage in the United States in 1972, there has been a slow recovery in eagle productivity, and currently, most populations are reproducing young at a rate that is adequate to maintain the population.
Lead poisoning may be a significant source of mortality in eagles. Lead shot accumulates in wetland areas where waterfowl feed, and are shot at by hunters. When bald eagles feed on these infirm, crippled, and dead birds, they in turn are poisoned. Over half the bald eagles necropsied during 1978-1981 died of lead poisoning, and many are probably suffering form sublethal effects. The use of lead shot by waterfowl hunters has been gradually phased out, and, as of the 1991-1992 hunting season, waterfowlers must use steel shot when hunting ducks anywhere in the United States. However, the effects of all the lead accumulated in sediments will be long lasting.
Collision with vehicles is the leading cause of death for individual bald eagles in Florida. In a survey of Florida bald eagle deaths from 1963-1984, nearly half were killed by motor vehicle impacts.
Other causes include egg collecting (a popular hobby at the turn of the century) and shooting (farmers and ranchers shot them for fear of livestock and poultry losses). In the 1960's, the major cause of eagle deaths nationwide was shooting.
However, the primary cause of population reduction and subsequent reason for the bald eagle's current protected status by federal and state agencies can be attributed solely to human activities. Much eagle habitat has been lost due to major ecological changes that have occurred in Florida, associated with wetland drainage and conversion, timber removal and/or conversion for agriculture and industry, and habitat destruction due to urban sprawl.
HABITAT GUIDELINES: Protection of this species consists of providing an effective zone that buffers the nesting sites. This "buffer zone" may extend into upland habitat. The extent of these buffers is based on existing State and/or Federal guidelines, or reflect the recommendations of the Florida Game and Fresh Water Fish Commission.
Any activity proposed within a buffer zone would be subject to review. Activities that could be allowed in the buffer zone would be those activities which would not have any long term detrimental impact on the nesting birds. The following would be considered when making this determination: (1) the type of activity or construction planned and its' long term impacts; (2) the nature of the natural community that makes up the buffer zone (does it provide a visual barrier for any proposed nesting activities?); and (3) the timing of the proposed construction (does it occur outside the nesting season?).
RECOMMENDATIONS: Due mainly to persistent conservation efforts and regulations protecting eagles and their habitat, populations have stabilized or increased in recent years. As a result, in 1994 the U.S. Fish and Wildlife Service re-classified the bald eagle from an "endangered" status to a "threatened" status.
Many recommendations for species and habitat management techniques have been suggested, including surveillance of nesting sites; research on the effects of pesticides, as well as their elimination; educational programs; management of individual populations; protection of roost areas; increased raptor protection and enforcement of laws; closing off nesting areas during incubation and when eagles are small; encourage private landowners to protect nesting sites; maintenance of suitable old trees for potential nesting sites; making provisions for eagle protection when land is transferred form federal to private or state ownership; not publishing locations of nests; elimination of hazardous perches on transmission lines; modification of predator traps so they do not crush the legs of raptors; prohibiting the hunting of wildlife by plane; research on wintering eagles; reintroduction in areas where eagles have been extirpated; and maintaining significant portions of communities where eagles occur in a relatively undisturbed condition.
A standard set of habitat management guidelines that directs the Florida Game and Fresh Water Fish Commission and U.S. Fish and Wildlife Service in dealing with developments that have the potential to threaten nesting eagles should be implemented throughout the county. These guidelines call for establishing protective zones around eagle nests, within which certain restrictions, from no disturbance at all to confining development activities to the non-nesting season, are imposed. Usually, the no-disturbance zone extends from 0.23 to 0.46 kilometers around a given nest, depending on circumstances at the nest, with a less restrictive zone extending an additional 0.46 to 1.60 kilometers outward.
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Nesbitt, S.A. 1990-1993. Bald eagle population monitoring. Annual Performance Reports. Statewide Wildlife Research, Study No. 7521. Florida Game and Fresh Water Fish Commission. 7pp.
Robertson, W.B., Jr. 1978. Southern bald eagle. Pp. 27-30. In H.W. Kale, II, (ed.), Rare and Endangered Biota of Florida. Birds. University Presses of Florida, Gainesville, FL.
U.S. Fish and Wildlife Service. 1987. Habitat management guidelines for the bald eagle in the Southeast region. Third Revision. U.S. Fish and Wildlife Service, Atlanta, GA. 8pp.
U.S. Fish and Wildlife Service. 1989. Southeastern states bald eagle recovery plan. U.S. Fish and Wildlife Service, Atlanta GA. 41pp. + 79pp.
Wood, P.B., D.A. Buehler and M.A. Byrd. 1990. Bald eagle. Pp. 13-21 in Proceedings of Southeast Raptor Management Symposium and Workshop. National Wildlife Federation, Washington, D.C.
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