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Bald Eagle

Haliaeetus leucocephalus
Overview
Minnesota Seasonal Status:

A regular breeding resident and migrant and formerly a winter visitant, the Bald Eagle is now regular in winter in southeastern Minnesota and other parts of Minnesota where open water is found, such as Lake Superior. The Bald Eagle was a common species during the Minnesota Breeding Bird Atlas (MNBBA).

North American Breeding Distribution and Relative Abundance:

The Bald Eagle is widely but patchily distributed across North America from Florida to the Maritime provinces, north and west to Alaska, and south to California. The species is rare in open country lacking water. Most prominent population centers are found along Pacific and Atlantic Coasts and inland lakes, reservoirs, and major river systems, in the upper Midwest in Minnesota and Wisconsin, and the Pacific Northwest (Figure 1).

Conservation Concern:
Conservation Status Score 9

Assigned a Continental Concern Score of 9/20 by Partners in Flight. The Bald Eagle was formerly listed as endangered in the United States except in Minnesota, Wisconsin, Michigan, Oregon, and Washington where it was threatened (1978). The state of Minnesota also listed it as threatened (1984). It has been delisted at both the federal and state level because of population increases, range expansion, and adaptation to human disturbance. The Bald Eagle is still protected under the federal Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act.

Life History
Migration:

Short- to medium-distance migrant that winters in the lower 48 states and in coastal areas of Canada, Alaska, and Mexico. The Bald Eagle is primarily found along major rivers, lakes, and reservoirs and wherever there is suitable open water.

Food:

Primarily fish and carrion but also large birds, mammals such as muskrats and hares, reptiles, amphibians, and crustaceans; occasionally garbage.

Nest:

Large trees with branches capable of holding the nest, cliffs, and on rare occasions on the ground.

Bald Eagle Bald Eagle. Haliaeetus leucocephalus
© David Brislance
Figure 1.

Breeding distribution and relative abundance of the Bald Eagle in North America based on the federal Breeding Bird Survey, 2011–2015 (Sauer et al. 2017).

Minnesota Breeding Bird Distribution*

Historically in Minnesota, Roberts (1932) reported that “records of forty to fifty years ago show that one or more pairs nested about nearly every large lake and here and there along large rivers throughout the wooded parts of the state.” In those earlier years, he stated the nesting Bald Eagle was even found occasionally in groves in the prairie regions near places with ample water. He cited such areas as the Des Moines River, Loon Lake, and Heron Lake in Jackson County, Otter Tail County, and the Red River valley as previous nesting areas. He quoted observations by Elliott Coues (1878), an early ornithological explorer in Minnesota: “While steaming down the Red River from Moorhead to Pembina, we frequently saw Bald Eagles sailing overhead, and several nests were noticed on the tops of tall, isolated trees.”

By the 1930s, Roberts reported that the “sight of an Eagle, except in some far-away place, has become a rare happening even during the seasons of migration.” He said that the “Bald Eagle aerie can be found only in remote or protected regions.” Roberts blamed the decline on the “settling of the state” and commented that the “rifle and gun have been the chief causes of its disappearance.” Hatch (1892) described the apparent widespread, cruel treatment of the Bald Eagle where “many a cabin in the solitudes of the deep, dark forests, has its young eagle chained to its gable, or the convenient out-house.” Referring to the citizens of Minneapolis, “it was no unusual thing to see individuals of the species chained, like a monkey, to a box or outhouse in different places in the city.”

Although Roberts reported the wide distribution of the species, he only described confirmed nests with young at Lake Minnetonka, Hennepin County (1874), and Itasca State Park (1902), plus “2 young” in Stearns County (1894). In his 1936 revision, Roberts added two confirmed nests, both with 2 young, detected by Nestor Heimenz in Crow Wing County, plus an “occupied nest” found by Marius Morse in Itasca County.

The status of nesting Bald Eagles was tenuous from the 1930s to the early 1960s. However, Mattsson (1988) provided an annotated list of historical Bald Eagle records from 1873 to 1959. These records represent a combination of observations of individual birds at specific locations and a variety of nesting data, such as whether a nest, a pair, or young was reported. In addition, pre-1976 Bald Eagle records in the Minnesota Department of Natural Resources heritage database were concentrated in the Chippewa National Forest, the Superior National Forest, and the Boundary Waters Canoe Area Wilderness, with additional observations from Aitkin, Clearwater, and southern St. Louis Counties (Miller and Pfannmuller 1991).

In their 1975 summary, Green and Janssen described confirmed nesting in 17 counties and inferred nesting in 2 counties. These included a summary of all county nesting records known at that time in Minnesota. The authors stated that the Bald Eagle was primarily a resident in the northern regions of the state and that the only known recent active nesting in the southern half of Minnesota was in the Upper Mississippi National Wildlife Refuge in Houston County. They emphasized the area producing the most young eagles was the Chippewa National Forest.

Johnson (1982) summarized Bald Eagle nesting data from 1960 to 1981 and identified 24 counties in which nesting occurred, from Houston County in the extreme southeast to Marshall County in the northwest and most counties in northern and northeastern Minnesota. Except for the Houston County record, no nests were found in most of the western counties or south of a line from Chisago County to northern Morrison and Otter Tail Counties. Johnson summarized nesting activity in the Chippewa National Forest from 1963 to 1981. The number of known nests in 1963 was 48, with 20 identified as active. This increased to 199 known nests and 75 active nests in 1981. The number of successful nests increased from 6 to 60 during this same period. In 1973, when statewide surveys were initiated, 115 known, occupied breeding areas were located (Coffin and Pfannmuller 1988; Miller and Pfannmuller 1991) and this increased to 437 occupied breeding areas and 300 successful nests in 1990.

Janssen (1987) summarized a breeding distribution similar to that described by Johnson (1982) and slightly expanded the number of counties with confirmed nests to 25. This included confirmed nesting since 1970 in Anoka, Sherburne, and Stearns Counties on the southern periphery of the species’ range. In 1998, Hertzel and Janssen would expand confirmed nesting of the Bald Eagle to 39 counties since 1970, with further extensions to the southwest as far as Brown, Lac qui Parle, Redwood, and Yellow Medicine Counties.

The Minnesota Biological Survey (MBS), which began in the late 1980s, has recorded 188 breeding season locations during its county surveys (Minnesota Department of Natural Resources 2017a). Breeding locations have spanned a considerable portion of the state, but by far the most locations are in the north-central and northern regions from Cook to St. Louis County. Several locations were noted along the Minnesota River.

Given Roberts’s pessimistic view of the Bald Eagle’s status in the 1930s, he would be surprised with the species’ spectacular recovery and the status of the Bald Eagle today. The MNBBA included a total of 2,113 records of the Bald Eagle. The species was recorded in every county except Lincoln and Pipestone in the extreme southwestern part of the state (Figure 2). The Bald Eagle was reported in 29.3% (1,432/4,886) of surveyed blocks and in 28.2% (660/2,337) of priority blocks (Figure 3; Table 1). Nesting was confirmed in an impressive 671 blocks, or 46.9% of all blocks where the species was recorded.

The MNBBA results have further expanded and now document the general breeding distribution of the Bald Eagle in Minnesota as of 2013. These results also provide evidence for recolonization of many areas in western, southwestern, southern, and southeastern Minnesota that likely were formerly occupied by the species. Many of these extensions were previously identified by Miller and Pfannmuller (1991), Hertzel and Janssen (1998), and the Minnesota Department of Natural Resources (2017b); however, the extent of the Bald Eagle’s range currently illustrated by the MNBBA is unprecedented in the documented history of Minnesota (Figure 2). Even though Roberts (1932) reported observations from Jackson County and the Red River valley, it is unknown how extensive Bald Eagle distribution was throughout the entire state in Roberts’s time.

In his review of the Bald Eagle in North America, Buehler (2000) stated that the present distribution of the Bald Eagle is probably similar to its historical breeding distribution. The story of the recovery of the distribution and population of the Bald Eagle in Minnesota is also similar to stories that have been documented in Michigan and Wisconsin and in Ontario (Cadman et al. 2007; Cutright et al. 2006; Chartier et al. 2013).

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

Figure 2.

Breeding distribution of the Bald Eagle in Minnesota based on the Breeding Bird Atlas (2009 – 2013).

Print Map
Figure 3.

Summary statistics of observations by breeding status category for the Bald Eagle in Minnesota based on all blocks (each 5 km x 5 km) surveyed during the Breeding Bird Atlas (2009-2013).

Breeding statusBlocks (%)Priority Blocks (%)
Confirmed671 (13.7%)232 (9.9%)
Probable46 (0.9%)29 (1.2%)
Possible309 (6.3%)203 (8.7%)
Observed406 (8.3%)196 (8.4%)
Total1,432 (29.3%)660 (28.2%)
Table 1.

Summary statistics for the Bald Eagle observations by breeding status category for all blocks and priority blocks (each 5 km x 5 km) surveyed during the Minnesota Breeding Bird Atlas (2009-2013).

Breeding Habitat

The Bald Eagle nests in large trees, often in the supercanopy and usually in old-growth or mature forests. In northern Minnesota, nest sites are usually within 0.8 km of water and are predominantly in white or red pines (Coffin and Pfannmuller 1988; Buehler 2000). In southeastern Minnesota, Mundahl et al. (2013) noted that of 53 nest trees that were used by the Bald Eagle, most were the tallest trees in the forest and were more than 50 m from water, and most successful nests were those with the surrounding forest containing basal area densities of greater than 20 m2/ha.

Formerly, the Bald Eagle was sensitive to human disturbance and land use near nest sites, so buffer zones were created to protect these sites (Mathisen et al. 1977). Recently, many birds appear to have adapted and tolerate human disturbance near nests in urbanized landscapes. Figure 4 is a typical picture of a Bald Eagle nest that has been used for many years. It is very close to a small town, in an open field, and within a half a kilometer of a large lake.

Typical nest site of the Bald Eagle in Minnesota (© Gerald J. Niemi).

Population Abundance

Over the past 150 years, the Bald Eagle has had a highly variable population history in Minnesota. In the late 1800s, Roberts reported it as common throughout the wooded portions of the state, as well as scattered where nesting trees and adequate water and food were available. As human settlements and land conversion began to expand in the late 1800s, available habitat was reduced and the population decline was further exacerbated by increased shooting (Evans 1982). This led Roberts (1932) to declare that the species was “formerly common, now much reduced in numbers and absent as a nesting bird from parts of the state where it once bred regularly.”

The passage of the federal Migratory Bird Treaty Act of 1918 and, later, the Bald and Golden Eagle Protection Act of 1940 may have reduced illegal shooting, but the use of DDT that began in the mid-1900s severely reduced the species’ populations (Carson 1962). Based on the paucity of reports, populations were very low and scattered in northern forested regions near selected large lakes and rivers. The banning of DDT in 1972 marked the start of the recovery for the Bald Eagle in Minnesota. Migration counts from Hawk Ridge in Duluth clearly indicate the recovery of the population (Figure 5). Migration counts at Hawk Ridge have increased by 7.81% per year from 1974 to 2012, with a slowing of the trend from 2000 to 2012 to 2.81% per year.

The Minnesota Department of Natural Resources (2006) completed surveys of active Bald Eagle nests from 1973 to 2005 and documented the substantial increase in the nesting population of the Bald Eagle in Minnesota. In 1973, the number of known active nests was slightly over 100; at the end of the Minnesota Department of Natural Resources surveys in 2005 the number of known active nests was 872. Based on a random survey of nests, the Minnesota Department of Natural Resources estimated that Minnesota had 1,312 total active nests in 2005.

Partners in Flight estimated a United States and Canadian population of 200,000 breeding adults (Partners in Flight Science Committee 2013). In contrast, Farmer et al. (2008) estimated a more conservative range of 100,000 to 1,000,000 birds. Environment Canada (2011) also indicated a more conservative population range for Canada of 50,000 to 500,000 adults. Rosenberg et al. (2016) estimated that the Bald Eagle population in the United States and Canada had increased by 113% from 1970 to 2014, while Farmer et al. (2008) indicated that populations appeared to be stabilizing in the northeastern United States. Trend signals were mixed in other parts of the United States, based on Christmas Bird Counts and the federal Breeding Bird Survey (BBS) (Sauer et al. 2017). The BBS was not used here because it was deemed unreliable for all states and regions and even survey-wide in North America. Density estimates are rare, but Mundahl et al. (2013) found a mean distance between nests of 1.52 km and densities ranging from 0.32 to 9.72 nests/100 km2 for 53 active nests in southeastern Minnesota.

Figure 5.

Raptor population index for the Bald Eagle based on fall migration counts at Hawk Ridge in Duluth, Minnesota, as calculated by the Raptor Population Index from 1974 to 2012.

Conservation

The Bald Eagle was listed as threatened when Minnesota’s first endangered species list was created in 1984 (Minnesota Department of Natural Resources 2017b). The Bald Eagle was listed as federally endangered in 1978, but as threatened in Minnesota. The Northern States Bald Eagle Recovery Plan had a goal of 300 occupied breeding territories in Minnesota, which was achieved in 1987 (Miller and Pfannmuller 1991). In 1996, because of the increased number of occupied breeding areas, the Bald Eagle was moved down on Minnesota’s state list to Special Concern status. Finally, the results of the Minnesota Department of Natural Resources surveys showing 872 active nests and estimating a total of 1,312 active nests in the state in 2005 helped justify the delisting of the Bald Eagle from the federal list of threatened and endangered species in 2007. The Bald Eagle was removed from the state list in 2013. However, the Bald Eagle and its nests are still protected under the Bald Eagle and Golden Eagle Protection Act and the Migratory Bird Treaty Act.

Even though the Bald Eagle is no longer listed, it still has many possible threats, and most are related to human activity (Minnesota Department of Natural Resources 2017b). DDT has been banned, but organophosphates, heavy metals, lead poisoning, and oil spills are continuing concerns. The Bald Eagle is still shot or intentionally poisoned. Collisions with vehicles have become a greater problem because the Bald Eagle frequently feeds on dead carcasses, especially deer, along roadsides. Many improvements have been made with electrical poles and power lines, but full implementation to retrofit this infrastructure has been slow, so raptors, including eagles, are still electrocuted. Finally, despite the tolerance of the Bald Eagle to human activity, protection of nesting, roosting, and wintering areas can still be a problem in some areas. Education of the public is an ongoing activity and is a focus of environmental education around Minnesota.  There is considerable management and conservation guidance available such as by the Minnesota Department of Natural Resources (2017b) and the United States Fish and Wildlife Service (2007).

Finally, Johnson’s (1982) clever insights are worth repeating. He stated that despite improvements in the Bald Eagle’s population, the potential damage from “environmental contaminants, urbanization, lakeshore development, agricultural expansion, shooting, trapping, lead poisoning, and nest disturbances” are ongoing. Indeed, since 1982 the species seems to be adjusting reasonably well to human settlements, but lead poisoning and contaminants loom as continuing issues of concern.

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