The Bald Eagle, a majestic symbol of North America, inhabits diverse environments, primarily near large bodies of water. While generally avoiding heavily developed areas, they are adaptable, often seen near fish processing plants, dumps, and dams where food is abundant. Their preference for tall, mature trees, especially conifers, offers excellent vantage points for spotting prey and surveying their territory. During winter, they may venture into drier, open uplands as long as access to open water for fishing remains available. This adaptability allows them to thrive across various landscapes, showcasing their resilience.
Habitat
Bald Eagles typically nest in forested areas adjacent to large bodies of water, seeking to avoid heavily developed regions. Their tolerance for human activity extends to feeding, where they may congregate around fish processing plants, dumps, and dams that concentrate fish. For perching, they favor tall, mature coniferous or deciduous trees that provide a wide view of their surroundings. In winter, Bald Eagles can also be found in dry, open uplands, provided there is access to open water for fishing.
Food and Diet
The cornerstone of the Bald Eagle’s diet is fish, with common species including salmon, herring, shad, and catfish. However, their diet is remarkably diverse, adapting to seasonal availability. They also consume birds, reptiles, amphibians, invertebrates like crabs, and mammals such as rabbits and muskrats. Bald Eagles are opportunistic hunters and scavengers, taking prey live, fresh, or as carrion. They are known to gorge on large meals, digesting them over several days, and can also endure fasting periods lasting many days or even weeks.
Nesting Habits
Nest Placement and Description
Bald Eagles predominantly nest in trees, unless regional constraints necessitate cliff faces or ground sites. They favor tall, sturdy conifers that rise above the forest canopy, facilitating easy flight access and providing excellent visibility. In warmer climates, they may utilize deciduous trees, mangroves, and even cacti. The specific process of nest site selection, whether by the male or female, remains unconfirmed. Nests are typically situated near the tree trunk, high up but below the crown, distinguishing them from Osprey nests.
These nests are among the largest built by any bird, usually measuring 5 to 6 feet in diameter and 2 to 4 feet in height. Their shape varies from cylindrical to conical to flat, depending on the supporting tree. Both male and female eagles contribute to gathering materials, though the female is primarily responsible for placement. They construct the nest by weaving sticks together and filling crevices with softer materials like grass, moss, or cornstalks. The interior is initially lined with lichen or fine woody material, followed by downy feathers and sometimes sprigs of greenery. Nests built on the ground utilize available materials such as kelp and driftwood near coastlines. The construction of a single nest can take up to three months, and they are often reused and expanded upon year after year.
Nesting Facts
- Clutch Size: 1-3 eggs
- Number of Broods: 1 brood per year
- Egg Length: 2.3-3.3 inches (5.8-8.4 cm)
- Egg Width: 1.9-2.5 inches (4.7-6.3 cm)
- Incubation Period: 34-36 days
- Nestling Period: 56-98 days
- Egg Description: Dull white, typically unmarked.
- Condition at Hatching: Chicks are covered in light-gray down, possess brown eyes, and have pink gaping mouths, legs, and skin.
Behavior and Social Structure
Bald Eagles are powerful and graceful fliers, adept at soaring, gliding, and covering long distances with impressive flapping techniques. Their courtship rituals are particularly spectacular, involving a synchronized aerial display where a male and female lock talons and cartwheel downwards, separating just before impact. Bald Eagles are known to harass other birds, including Ospreys and other eagles, to steal their prey. They will also engage in similar tactics with mammals like river or sea otters.
On the ground, their gait is described as awkward and rocking. They are capable of floating and can use their wings to “row” through water that is too deep for wading. While often seen alone, Bald Eagles do congregate in large numbers at communal roosts and feeding sites, especially during winter. These gatherings can be boisterous, with frequent jostling for position and disputes over prey. During the breeding season, they vigorously defend their territories against various intruders, including raptors, ravens, coyotes, and foxes. When feeding at carcasses, Bald Eagles may assert dominance over Black and Turkey Vultures, and other scavengers such as ravens, coyotes, bobcats, and dogs may also compete for food. Despite their formidable nature, Bald Eagles are sometimes harassed or chased by fellow raptors and smaller birds like blackbirds, crows, and flycatchers. Learn more at Birds of the World.
Conservation Status and Success
The recovery of the Bald Eagle is a remarkable conservation triumph. Between 1966 and 2019, their numbers saw an annual increase of nearly 4%, according to the North American Breeding Bird Survey. Estimates suggest a global breeding population of around 200,000, with over 316,000 individuals in the Lower 48 states as of 2021. The species is considered of low conservation concern, reflected in its score on the Continental Concern Index.
Historically abundant, the Bald Eagle population plummeted in the mid-to-late 20th century due to trapping, shooting, poisoning, and reproductive issues linked to pesticide use, particularly DDT. By 1978, they were listed under the Endangered Species Act. However, protective measures enacted since 1980, including the ban of DDT and improved human treatment, have facilitated a dramatic resurgence. By the late 1990s, Bald Eagles were re-establishing populations across most of North America, leading to their removal from the Endangered Species list in June 2007.
Ongoing threats include lead poisoning from ammunition in hunted prey, collisions with vehicles and structures, and habitat destruction due to development along shorelines. Environmental pollution also remains a concern, as evidenced by the Exxon Valdez oil spill in 1989, which led to significant Bald Eagle mortality. Fortunately, the Prince William Sound population returned to pre-spill levels by 1995, demonstrating resilience.
Credits
- Buehler, D. A. (2000). Bald Eagle (Haliaeetus leucocephalus). In The Birds of North America, No. 506 (A. Poole and F. Gill, Editors). The Birds of North America, Inc., Philadelphia, PA, USA.
- Dunne, P. (2006). Pete Dunne’s essential field guide companion. Houghton Mifflin Harcourt, New York, USA.
- Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
- Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
- Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
- Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.
