The life history of bald eagles can be broadly categorized into breeding and non-breeding periods. The breeding period varies by latitude; in Alaska it begins with courtship and nest building in February and ends when the young fledge by late August into early September. The young are attended by the adults near the nest for several weeks after fledging. The non-breeding period begins once the young fledge in the fall and lasts until adults resume breeding activities in the spring, roughly mid-September through January. The nesting period, when avoiding disturbance to eagles is most critical, is defined as March 1 through August 31 in Alaska.
During the breeding period, breeding bald eagles occupy and defend territories. A territory includes an in-use nest and may include one or more inactive, alternate nests that are built or maintained but not used for nesting in a given year. Bald eagles generally nest near coastlines, rivers, and large lakes where there is an adequate food supply. Nests are built on trees (with a preference for mature or old-growth trees), snags (dead trees), cliffs, and rock promontories, usually with a dominant view of the surrounding landscape. Rarely in Alaska, bald eagles nest on artificial structures such as power poles and communication towers. In forested areas, bald eagles often select the tallest trees with limbs strong enough to support a nest that can weigh more than 1,000 pounds. Nest territories typically include at least one perch with a clear view of the water, where eagles forage. Eagle nests are constructed with large sticks and may be lined with moss, grass, plant stalks, lichens, seaweed, or sod. Nests are usually about 4 to 6 feet in diameter and 3 feet deep, although larger nests exist.
The bald eagle breeding period consists of 5 phases:
- Courtship and nest building
- Egg laying and incubation
- Early nestling (up to 6 weeks post hatch)
- Late nestling (more than 6 weeks post hatch)
Dates vary (see table below), but generally egg-laying begins in April in Alaska. Clutch sizes range from 1 to 3 eggs. Successful pairs usually raise 1, 2, or, rarely, 3 young per nest. Eaglets make their first unsteady flights about 10 to 12 weeks after hatching and fledge (leave their nests) within a few days after that first flight. The time between egg-laying and fledging is approximately 4 months. Young birds usually remain in the vicinity of the nest for several weeks after fledging because they are dependent on their parents for food until they disperse from the nesting territory approximately 6 weeks later. The entire breeding cycle, from initial activity at a nest through the period of fledgling dependency, is about 6 months
Bald Eagle Breeding Chronology Within Alaska1
Courtship and nest building
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Egg laying and incubation
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Start Mar 1
End May 15
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Start Apr 15
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1Dates in the table represent the range of possible dates for a given activity. The nesting period, when avoiding disturbance to eagles is most critical, is defined as March 1 through August 31 in Alaska.
Eagle sensitivity to humans and other sources of disturbance varies among these 5 phases, with eagles being most sensitive to disturbance during the egg laying and incubation and late nestling phases. Sensitivity also varies among individual eagles and pairs of eagles within each phase. Some pairs, for example, nest successfully near human activity, while others abandon nest sites in response to activities much farther away. This variability may be related to a number of factors, including visibility of the activity, duration and noise level of the activity, extent of the area affected by the activity, the eagle pair’s prior experiences with humans, and tolerance of the individual nesting pair. Despite this variability, the sensitivity of bald eagles can be generally described within each breeding phase.
Relative Sensitivity of Nesting Bald Eagles to Human Activities
Courtship and nest building
Moderately sensitive period
Disturbance is manifested in nest abandonment. Bald eagles in newly established territories are more prone to abandon nest sites.
Egg laying and incubation
Most sensitive period
Human activity of even limited duration may cause nest desertion and territory abandonment for the nesting season. Flushed adults leave eggs unattended, and eggs are susceptible to thermal stress, loss of moisture, and predation.
Moderately sensitive period
Adults are less likely to abandon the nest near and after hatching. However, flushed adults leave young unattended and vulnerable to weather and predators. Nestlings may miss feedings, which may affect their survival.
Very sensitive period
Gaining flight capability, nestlings 8 weeks and older may flush from the nest prematurely due to disturbance and die.
Moderately sensitive period
While learning to fly, fledglings are vulnerable to disturbance by humans and may be more likely to be injured when trying to escape disturbance. This risk diminishes with time as fledglings become proficient at flight.
Bald eagles may respond in a variety of ways when they are disturbed by human activities. During the nest building period, for example, eagles may inadequately construct or repair their nest or may abandon the nest, both of which can lead to failed nesting attempts. During the incubation and hatching period, human activities may startle adults or cause them to flush from the nest. Startling can damage eggs or injure young when the adults abruptly leave the nest.
Prolonged absences of adults from their nests can jeopardize eggs or young. Depending on weather conditions, eggs may overheat or cool and fail to hatch. Young nestlings rely on their parents to provide warmth or shade and may die from hypothermia or heat stress if adults are forced away from the nest for an extended period of time. Eggs and juveniles are subject to greater predation risk while they are unattended.
If human activities disrupt the adults’ foraging and feeding schedule, the young may be malnourished, affecting their development and ultimate survival. Older nestlings may be startled by loud or intrusive human activities and prematurely jump from the nest before they are able to fly or care for themselves.
Any negative impacts to productivity caused by disturbance (including failed nesting attempts, damage or loss of eggs, and injury to young, including due to weather effects or malnourishment) constitute take under the Bald and Golden Eagle Protection Act (see below).
Avoiding Bald Eagle Disturbance at Nest Sites
To avoid disturbing nesting bald eagles, we recommend that you (1) avoid certain activities during the nesting season (defined as March 1 through August 31 in Alaska) to the extent practicable, (2) conduct certain activities at recommended distances from in-use nests, and (3) maintain natural forested or vegetative buffers around nest trees or make use of topographic buffers. The buffer areas should be applied to both in-use and inactive, alternate nests and serve to minimize visual and auditory impacts associated with human activities near nest sites.
The impact that a new human activity has on a pair of nesting eagles depends on whether the eagles can see or hear the activity from the nest and on how tolerant the birds are to human activity. Eagles are more prone to disturbance when an activity occurs in full view. For this reason, we recommend that projects locate activities farther from the nest in areas with open vistas than in areas where line of sight from the nest to the activity is shielded by rolling topography, trees, or other screening factors. Also, vegetative buffers should be large enough to protect existing nest trees, including their root , and provide for alternative or replacement nest trees. Sudden and loud noises can also lead to disturbance, and these should be considered along with topography and other characteristics surrounding the nest site when determining the size and shape of effective buffers. For example, in open areas where there are few trees or other, natural buffers, distance may be the only buffering option. Consequently, the buffers in open areas may need to be larger than for areas with denser vegetation or other natural screening.
In addition to the physical features of the landscape, appropriate buffer size may vary according to the historical tolerances of eagles to human activities in particular localities and may depend on the location of the nest in relation to feeding and roosting areas used by the eagles. Bald eagles that repeatedly choose to nest in the vicinity of ongoing human activities may be more tolerant of a greater degree of human activity than eagles in areas that experience fewer human impacts. Comparing proposed activities to existing activities can help determine whether a pair may be sensitive to a given project.
Due to noise sensitivity, we recommend seasonal restrictions for many temporary activities that do not involve habitat alterations (e.g., fireworks, outdoor concerts, blasting, pile driving). Potential negative impacts can be avoided by restricting these kinds of activities to the non-nesting period (defined as September 1 through February 28 in Alaska). For activities that include both temporary and permanent habitat disturbance (e.g., building construction, timber harvest, vegetation clearing), we recommend a combination of landscape buffers and seasonal restrictions.
Human activities that lead to injury, a decrease in productivity, or nest abandonment are considered disturbance under and a violation of the Bald and Golden Eagle Protection Act. For activities that have the potential to disturb nesting eagles during the peak nesting season (defined as March 1 through August 31 in Alaska; https://www.fws.gov/alaska-bird-nesting-season), you may need a permit from the Fish and Wildlife Service. For questions about avoiding or minimizing disturbance and the potential need for a permit, please contact your local Field Office in Anchorage or Fairbanks.
In the fall, bald eagles in many parts of Alaska begin moving to their wintering grounds as lakes and rivers begin to freeze and prey becomes limited. Wintering grounds for migratory Alaska eagles have not been identified with certainty, but it is suspected that bald eagles breeding in Interior Alaska winter in Coastal Alaska and British Columbia, Canada. Eagles breeding in Coastal Alaska may remain in the vicinity of their nest sites throughout the year. Immature eagles wander more widely in search of food. The majority of wintering eagles are found near open water where they feed on fish, marine invertebrates, and waterfowl, often taking dead, crippled, or otherwise vulnerable animals. Mammalian carrion is an important alternative source of food at some locations. An abundant, readily available food supply in conjunction with one or more suitable night roost sites are the primary characteristics of winter habitat.
At night, wintering eagles may congregate at communal roost trees. Roosts are found in locations that are protected from the wind by vegetation or terrain, providing a more favorable thermal environment. The use of these sheltered sites helps minimize the energy stress encountered by wintering birds. Communal roosting may also assist eagles in finding food. The same roost trees are used for several years. Although the location of communal roosts is poorly documented in Alaska, activities that could result in habitat disturbance should be sited to avoid known or suspected roosts.
Bald eagles are not as sensitive to human disturbance during migration or the winter as they are during the breeding period. However, wintering bald eagles congregate at specific sites year-after-year for feeding and sheltering. Bald eagles rely on these established roost sites because of their proximity to sufficient food sources. Permanent landscape changes may eliminate these areas and force bald eagles to seek out other wintering roost and foraging areas. Depending on the proximity of other suitable roost or foraging areas and the condition of the affected eagles, loss of these areas can harm bald eagles. In addition, human activities near or within communal roost sites may prevent eagles from feeding or taking shelter, even if the activities do not physically alter the habitat.
Consult the National Bald Eagle Management Guidelines if you have additional questions about bald eagle management in Alaska or the lower 48 states. Please note that the dates and sensitivities categories presented in the Chronology and Sensitivity tables above differ from the information presented in the National Guidelines to better align with different climatic factors, the large geographic scale of Alaska, and local expert opinion.
Bald Eagle Nest Atlas
The Bald and Golden Eagle Protection Act prohibits the take of eagles, their nests, and eggs either directly, such as by shooting, or indirectly, such as by disturbance of nesting eagles without a permit. Nest surveys for bald eagle have been conducted in Alaska since the 1960s to locate nest sites so land managers can protect them in compliance with the Act. Extensive surveys have historically been conducted in some regions of the state, including southeastern Alaska, Kodiak Island, the Kenai Peninsula, Alaska Peninsula, Prince William Sound, and several mainland rivers.
For many years, survey results were kept on maps and data cards in various offices scattered across Alaska. It was difficult for managers to locate survey information or know what had been surveyed. With current technologies, it is now possible to make this information readily available to many more users. The Bald Eagle Nest Atlas displays bald eagle nests documented by the Fish and Wildlife Service and others. Please note that the map is not intended to take the place of a survey to determine the presence or absence, status, or exact location of a current eagle nest. Current eagle nests and potential habitat may or may not overlap with the nesting areas shown. Please contact Steve Lewis with questions about the map or for information on nest locations.