I examined bald eagle habitat structure and components to determine America’s national bird daily and annual habitat preferences.
Specifically, this article looks at:
What constitutes bald eagle habitat?
Bald eagle habitat is virtually any body of water that is large enough to support an abundant and diverse food base. The ideal bald eagle habitat is a water body surrounded by tall trees that eagles use to spot their prey from. Bodies of water that attract bald eagles include rivers, dams, lakes, lagoons, coastal estuaries, and tidal marshes.
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Factors that determine suitable bald eagle habitat
Studies on bald eagle habitat have identified three essential components:
- Abundance, Diversity, and Vulnerability of the prey base
Bald eagles feed primarily on fish but are opportunistic and take waterfowl, small mammals, and carrion when available. Where fish and other prey are abundant, they are generally easy to take, and more animals are regularly dying, hence more carrion available. An abundance of the prey base is perhaps the most important component of suitable bald eagle habitat.
- Aquatic habitat features such as shallow water
Shallow water is essential because fish is easier to detect and catch. Tidal shallow water often leaves fish stranded during low tides, becoming easy prey for bald eagles. Bodies of water less than 6 feet deep appear to attract more eagles.
Large concentrations of waterfowl in shallow water are easier to catch. Waterfowl tend to dive underwater upon being attacked by aerial predators. In very shallow water, concentrations of waterfowl have nowhere else to go and become vulnerable to eagles.
- Absence of human development and disturbances
Where human development has taken over shorelines, bald eagles no longer have the tall perches and large trees they need to overlook the water for prey and to nest.
The height of trees around bodies of water is important as perches for eagles to spot their prey. However, tall trees become less important when a body of water supports a large prey base. In the absence of tall trees, bald eagles perch on logs, rocks, or anything slightly elevated from the ground.
Ideal eagle perches
The best perches for bald eagles are usually easily accessible and close to shorelines. The more common types of trees include conifers and deciduous species, and any other type of tree is used by eagles when available.
Live trees tend to be used for perches. However, when available, dead trees are preferred, apparently because they offer easy access and take off and allow for an unobstructed view of more expansive areas. The trees selected for daily perches are more variable in type and sizes than those chosen perches for roosting.
As more antennas, communication towers, buildings, and other human-made structures become part of bald eagle habitats, birds appear to get used to and use them as perches.
Breeding or nesting bald eagle habitat
Bald eagles breed primarily in forested areas near water bodies—Eagles nest in trees and rarely on cliffs. In treeless areas, bald eagles nest on cliffs, steep hills, and on the ground.
Birds typically build their nests in old-growth forests within less than 2 kilometers of the water where sufficient foraging opportunities exist. However, the body of water’s quality, or the amount of prey it supports, has to do with the distance bald eagles are willing to travel. When suitable nesting trees are not available near good water bodies, bald eagles place their nests farther and travel long distances to where good foraging opportunities exist.
Bald eagle habitat studies suggest that lakes of more than 3.8 square miles (10 square km) may be optimal habitats for breeding bald eagles. However, longer and narrower lakes and other water bodies can support breeding eagles as well.
Generally, bald eagle nests are farther from the shoreline in areas with substantial development or human activity than nest sites in less developed areas.
Bald eagle wintering habitat
Some bald eagle populations migrate to other regions and habitats, while others remain in the same habitat throughout the year. Wintering birds usually congregate in large numbers (up to 1,000s) in areas near large river systems in the midwestern and Pacific Northwest, Chesapeake Bay, Kasomath Basin, Oregon-California, and the intermountain west.
Water Bodies are preferred wintering habitats, although arid areas of the Southwest may also be used.
Key factors that influence winter habitat suitability include the availability of food, roost sites, and the absence of human disturbances.
Throughout the wintering range, the amount of prey varies greatly. Some areas are places where there is considerable human activity. Still, bald eagles will tolerate some human activity in situations where prey is readily available such as dams on the Missouri or Mississippi Rivers.
The types of perches eagles use are similar during the wintering and the breeding seasons.
Bald eagle roosting Habitat
The bald eagle usually chooses open, tall trees of easy access for roosting. Generally, roost trees are either deciduous or coniferous, with a diameter of 12 to 39 inches and a height of 16 to 66 yards.
Several differences exist between the characteristics of nesting and roost-sites. While nesting sites are generally associated with aquatic foraging areas, roosts are typically located further from the water, especially in western states. An example of this would be a roosting site in Utah located 29 km from the main foraging area. Several other western roosts are more than 10 kilometers from foraging areas. Foraging areas of the Chesapeake Bay and N. Carolina were up to 1 km away from roosts.
Bald eagles prefer to roost far from houses and roads. At the Chesapeake Bay, roosts are surrounded by relatively large forests but are adjacent to large, open flight corridors that allow easy access.
Most roosts are found in deciduous trees situated away from prevailing winds. Eagles may select communal roosts due to site characteristics that facilitate social interaction, such as information exchange.
Threats to bald eagle habitat
A significant cause of bald eagle habitat loss is human development, which takes over shorelines with nesting, perching, roosting, and aquatic foraging habitat. Increasing development and human population density may limit the number of eagles that can live in some areas.
It is unknown whether bald eagles react to the development structure itself or the associated human activity. Almost any human development along the shoreline of rivers, lakes, or coastal areas provides access to open water for recreational activities. Open water happens to be where bald eagles find food.
Most bald eagles avoid areas developed by humans. Abandonment of foraging areas, roosts, and nesting sites may also result from repeated disturbances associated with human activities.
Bald eagle numbers are also affected by direct alteration of their habitat. In Canada, for example, the construction of hydroelectric dams where bald eagle populations are well established reduced the amount of habitat available for eagles.
Bald eagles can also benefit from human activities. Where aquatic habitats are scarce, dams and water storage facilities often increment bald eagle foraging and breeding habitat.
Bald eagle tolerance of human activities
Balde eagle tolerance of human development varies widely and may be increasing in some areas. Direct human persecution such as shooting and harassment at their nesting sites reinforces eagle avoidance behavior. But, a reduction of human persecution and disturbances may relax eagle avoidance behavior.
Some bald eagles populations have become more tolerant of human development and human activities. They forage and nest in human-occupied habitats they previously avoided.
Eagle biologists in Florida recognize two groups of bald eagles; urban and rural eagles. While rural eagles are skittish and react to human disturbances near their nest sites, urban eagles are tolerant of most human activities. Eaglets that hatch and grow among human activities are more likely to feed and nest in similar habitats when they become adults.
How does climate change affect bald eagle habitat?
After recovering from the brink of extinction in the lower 48 states the bald eagle will be facing a new challenge: climate change. Climate change will result in frequent extreme wet and dry cycles threatening the aquatic ecosystems that they depend on.
Audubon scientists indicate that droughts will affect rivers, lakes, and wetlands; subsequently, the bald eagle’s food source.
Researchers say that climate change adds to extreme weather, including windstorms that may endanger nests and eaglets. Periods of extreme heat in the south may exacerbate drought conditions making it more difficult for eagles to reproduce.
With global warming at its current rate, scientists estimate that in 60 years, the bald eagle’s breeding range will move north. Breeding habitat will shift into Canada and Alaska as the lower 48 states become less ideal for breeding.
Buehler, D. A. (2020). Bald Eagle (Haliaeetus leucocephalus), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
Fraser, J. D., L. D. Frenzel and J. E. Mathisen. (1985). The impact of human activities on breeding Bald Eagles in north-central Minnesota. Journal of Wildlife Management 49:585-592.
Livingston, S. A., C. S. Todd, W. B. Krohn and Jr. Owen, R. B. (1990). Habitat models for nesting Bald Eagles in Maine. Journal of Wildlife Management 54:644-653.
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