The Bald Eagle (Haliaeetus leucocephalus) is the second largest bird of prey in North America (only the Golden Eagle is larger). Adult Bald Eagles have a distinctive white head, dark brown body and wings, and white tail. They have bright yellow legs and feet that are un-feathered and equipped with long, sharp, black talons for penetrating and grasping prey. Adult Bald Eagles also have a powerful, bright yellow, hooked bill that is used for tearing and dismembering prey. Immature Bald Eagles have a dark brown head, body, wings, tail, feet, and bill. They are predominantly dark brown birds with limited white mottling on the underside of wings and belly. Bald Eagles reach adult plumage at about five years. Adult Bald Eagles are unmistakable but immature Bald Eagles are often mistaken for Golden Eagles.
Bald Eagle flight is distinguished by soaring and slow, methodical, powerful wing-beats (Buehler 2000). They soar with their wings on a flat plane as opposed to a convex plane like the turkey vulture. They have keen eyesight that is about eight times more powerful than a human's eyesight. Average life span in the wild is unknown, but 30 years is a reasonable estimate of potential longevity under natural conditions. Eagles have been known to survive in captivity for nearly 50 years.
Bald Eagles were historically found in all 50 states except Hawaii and nested in 45 of the 48 contiguous states. The species suffered severe population declines across the country in the late 1800s. Land development altered habitat as settlers moved west. Unregulated hunting contributed greatly to the decline of the bald eagle during this time. Later, in the 20th century a new and more serious threat appeared. The use of pesticides, such as Dichloro-Diphenyl-Trichloroethane (DDT) and other environmental contaminants caused major population declines for many species. The bio-accumulated pesticide softened eggshells resulting in low reproductive success (Buehler 2000).
In 1940 the Bald and Golden Eagle Protection Act (BGEPA) was signed and prohibited hunting, possession, or sale of eagles. In response to the continued declines the U.S. Fish and Wildlife Service (USFWS) listed the species as federally endangered on 14 February 1978 (Buehler 2000, USFWS 2006) under the Endangered Species Act (ESA) of 1973 (16 U.S.C. 1531-1544). Along with its listing under the Federal ESA the Bald Eagle was also listed as endangered under the Nebraska Nongame and Endangered Species Conservation Act in 1978. In 1972 the use of several chlorinated hydrocarbon pesticides, including DDT, was banned in all fifty states.
After receiving state and federal protection, and with the banning of DDT and other similar chemicals, Bald Eagle numbers began to increased (Millar et al. 2007). In 1963 there were an estimated 417 breeding pairs in the lower 48 states and by 1997 that number jumped to 7,066 (Buehler 2000, USFWS 2006). In response to the increase, the USFWS reclassified the species as threatened in 1995, and the Nebraska Game and Parks Commission (Commission) reclassified the Bald Eagle as threatened in Nebraska in 2000. The Bald Eagle was formally removed from the federally threatened and endangered species list on 28 June 2007. At the time of delisting, there were an estimated 9,000 breeding pairs in the lower 48 states (Millar et al. 2007). In 2008 the Bald Eagle was removed from Nebraska’s threatened species list.
In Nebraska, the first modern report of breeding activity was in 1973 (Lock and Schuckman 1973). However, the first successful modern nesting did not occur until 1991 in Douglas County when an eaglet fledged from a nest near Valley. Since 1991, the number of active nests has increased each year at an average rate of 29%. In 2007, there were 51 active nests in Nebraska. The 2011 data is not yet completed but the current number of active nests already surpasses the 2010 record of 54 active nests. The 274 nests observed in Nebraska from 1991 to 2007 fledged an average of 1.85 eaglets. In 2010 a record 54 active Bald Eagle nests were found in Nebraska with a season fledge ratio of 1.92 eaglets per nest.
The map below is a visual representation of ACTIVE BALD EAGLE NESTS
Nebraska’s wintering Bald Eagle population is highly variable from year to year in response to weather. However, even with these variations the number of Bald Eagles occurring in Nebraska during the non-breeding season has increased during the last several decades. In the mid 1900’s Bald Eagles were considered an uncommon migrant and winter resident; today Bald Eagles are considered common migrants and winter residents. From 1980 to 1995 an average of 744 Bald Eagles were counted in Nebraska during the annual midwinter surveys. From 1996 to 2011 the average increased to 990 Bald Eagles.
Most people envision this majestic bird skimming along the surface of a lake or river and suddenly snatching an unsuspecting fish. Bald eagles frequently feed this way, but also are quick to exploit more easily obtained food sources. Bald Eagles obtain food by direct capture, scavenging, and stealing from other Bald Eagles, other birds, or from mammals (Buehler 2000). Fish are the Bald Eagle's primary source of food, but the fish do not need to be alive to attract an eagle's attention. Winter die off of fish at some of Nebraska's lakes and reservoirs provide readily available forage. Waterfowl are another important source of winter food. When severe winter weather causes a previously reliable food source to become unreliable, Bald Eagles hunt uplands for birds or mammals, or they scavenge. If severe conditions persist, eagles concentrate in the few remaining open-water areas or migrate farther south. Bald Eagles can devour large amounts of food at one time and then store the food in their crop (Buehler 2000). They can then digest the food over the period of several days. They can also go without food for several days.
Bald Eagles are monogamous and are thought to mate for life. They have spectacular courtship rituals where they use vocalizations and perform acrobatic flight displays. The most noted courtship act is called the “cartwheel display,” which is when the courting pair flies high in the air, lock talons, tumble back down toward earth, and then break apart at the last minute to avoid collision with the ground (Buehler 2000).
Bald Eagles have one brood per season, and the clutch size generally ranges from one to three eggs. A replacement clutch is possible if the eggs are taken or destroyed during the incubation period. Bald Eagle’s incubation period is generally 35 days and the female does a majority of the incubation. From the time eggs are laid until about six weeks after the eggs hatch the adults are very territorial and protective of their nesting territory. Both male and female defend the nest territory. Territorial defense mechanisms include perching in prominent locations, using threat vocalizations, and chasing intruders out of the area (Buehler 2000).
For the first two to three weeks after eggs hatch at least one adult is at the nest tending to the nestlings at all times. During this time the males does most of the hunting and provides most the food while the female tends to the young. After about five to six weeks parental care declines and adults roost away from the nest, usually in an adjacent tree (Buehler 2000).
Nesting or wintering Bald Eagles are found in close association with water. Rivers, lakes or reservoirs that provide a reliable food source and isolation from disturbing human activities are preferred. Large trees and snags along shorelines provide feeding and loafing perches and potential nest sites. All Bald Eagle nests in Nebraska have been constructed in cottonwood trees. Larger stands of mature trees that are free from disturbance, provide adequate perches, and adequate protection from the winter elements are needed for communal winter roosting.
During the fall and spring migration, when most water areas are ice free and milder weather conditions predominate, Bald Eagles may be seen along virtually any waterway or impoundment in Nebraska. During the critical wintering period (December 15 to February 20), eagles are usually forced to concentrate in areas where waters remain free of ice and food is available.
The Bald Eagle has no known natural enemy, but human activities have posed a large threat to Bald Eagles in the past. The decline in Bald Eagles across the nation that occurred in the late 1800s and early 1900s was primarily due to unregulated hunting. In spite of the substantial fines and jail time that can be charged to someone that shoots a Bald Eagle today, shooting remains a cause of death.
The nationwide decline of Bald Eagles that took place from the 1940s into the early 1970s was a result of contaminant buildup in the environment related directly to the agricultural and industrial use of pesticides and chemicals. Contaminant residues, especially from DDT, were found in adult birds, eggs and nestlings as well as in the eagles' food sources. Contaminants in adult Bald Eagles result in abnormal breeding behavior, thin eggshells and dead embryos within the eggs. Other pesticides, such as Dieldrin and Endrin, were implicated most often in acute poisonings, those resulting in immediate death of individual birds.
Lead poisoning from the ingestion of spent lead shot and fishing sinkers has been identified as a source of mortality in waterfowl. Eagles have died from lead poisoning after feeding on dead or crippled waterfowl and ingesting lead pellets imbedded in the waterfowl's flesh or gizzard. Bald Eagles can also obtain lead poisoning by consuming dead or crippled upland game, such as deer, that had been shot with lead ammunition. Collisions with power lines are another direct cause of bald eagle mortality in Nebraska and throughout the country. In the first four years of Nebraska's Raptor Electrocution Prevention Program in the late 1980’s and early 1990’s, cooperators documented nearly 45 electrocuted Golden Eagles and Bald Eagles.
Bald Eagles can be seen year-round across the state of Nebraska. However, winter and early spring is the best time of year to see numbers of Bald Eagles. An excellent strategy is to visit any large reservoirs in early spring once there is some open water and once migrating waterfowl have arrived. Reservoirs that possess some ice are ideal. This usually occurs in late February or early March. In the winter, November through January, concentrations of Bald Eagles often occur at reservoirs that maintain some open water. Favored sites include Sutherland Reservoir near North Platte, Harlan County Reservoir near Alma, and below Gavin’s Point Dam near Yankton, South Dakota. Lake Ogallala and Lake McConaughy are also a favored site and Central Nebraska Public Power and Irrigation District (CNPPID) maintains a viewing building near the dam spillway. CNPPID also facilitates viewing at their J-2 power plant near Lexington.
Resident Bald Eagles may build or repair nests any time of the year, but activity generally increases from December through February. Nesting Bald Eagles in Nebraska typically will have eggs by early March. Occasionally eagle pairs, which are likely inexperienced birds, build a nest but do not lay eggs. If you do discover an active Bald Eagle nest please do two things:
1) View the birds from a distance using a spotting scope or
binoculars. Do not disturb the birds; doing so may be a violation
of federal law. If you have questions about how close or what
activities are acceptable in the vicinity of a Bald Eagle nest,
please contact the U.S. Fish and Wildlife Service Nebraska Field
Office at 308-382-6468.
The recovery of the Bald Eagle is considered a modern conservation success story. This species has greatly surpassed recovery objectives and the number of breeding pairs in Nebraska is expected to continue to increase into the future. Current and potential threats have apparent minimal impact on population growth. The Bald Eagle has been removed from both the federal and state list of threatened and endangered species.
Literature Cited Buehler, D.A. 2000. Bald Eagle (Haliaeetus leucocephalus), In The Birds of North America, No. 506 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Harmata, A.R. 1984. Bald Eagles of the San Louis valley, Colorado: their winter ecology and spring migration. Ph. D. diss., Montana State University., Bozeman.
Lock, R.A. and J. Schuckman. 1973. A Bald Eagle nest in Nebraska. Nebraska Bird Review 41: 76-77.
Millar, J., et al. 2007. Daft post-delisting monitoring plan for the bald eagle, (Haliaeetus leucocephalus). U.S. Fish and Wildlife Service. http://www.fws.gov/migratorybirds/issues/BaldEagle/PostDelistingMonPlan.pdf, accessed 13 May 2008.
United States Fish and Wildlife Service. 2006. Endangered and threatened wildlife and plants: removing the Bald Eagle in the lower 48 States from the list of endangered and threatened wildlife.