The life cycle of bald eagles in Alaska is characterized by distinct breeding and non-breeding periods, with significant variations based on latitude. Understanding these periods is crucial for effective conservation efforts, particularly concerning human activities around nesting sites. The breeding season in Alaska typically spans from February to September, while the non-breeding period extends from September through January, following the fledging of young eagles. During the critical nesting period, from March 1 to August 31, avoiding disturbance to these magnificent birds is of utmost importance.
Breeding Period: Territory, Nesting, and Sensitivity
During the breeding season, bald eagles actively defend their territories, which encompass an active nest and potentially several inactive ones. They show a preference for nesting near abundant food sources, such as coastlines, rivers, and large lakes. Nests are commonly built in mature trees, snags, cliffs, or rock promontories, offering a dominant view of the surrounding landscape. In rare instances in Alaska, nests can be found on artificial structures like power poles or communication towers. Within forested areas, bald eagles often select the tallest trees capable of supporting nests that can weigh over 1,000 pounds. These territories usually include a perch with a clear view of the water for foraging. Eagle nests are substantial structures, typically 4 to 6 feet in diameter and 3 feet deep, constructed from large sticks and sometimes lined with moss, grass, or other natural materials.
The bald eagle breeding cycle in Alaska unfolds over five distinct phases: courtship and nest building, egg laying and incubation, early nestling (up to 6 weeks post-hatch), late nestling (over 6 weeks post-hatch), and fledgling. Egg laying generally commences in April, with clutch sizes ranging from one to three eggs. Successful pairs typically raise one or two young. Eaglets take their first flights around 10 to 12 weeks after hatching and fledge shortly thereafter. The entire process from egg-laying to fledging, including the period of parental dependency for about six weeks after fledging, spans approximately six months.
The sensitivity of bald eagles to human disturbance varies significantly across these breeding phases. Eagles are most sensitive during egg laying, incubation, and the late nestling stages. Disturbance can lead to nest abandonment, premature flushing of young, and missed feedings, all of which can negatively impact chick survival and development. Factors such as the visibility, duration, and noise level of human activities, along with the eagles’ prior experiences and individual tolerance, influence their response to disturbance.
| JAN | FEB | MAR | APR | MAY | JUN | JUL | AUG | SEP | OCT | NOV | DEC |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Courtship and nest building | Start Feb 1 | End Apr 30 | |||||||||
| Egg laying and incubation | Start Mar 1 | End May 15 | |||||||||
| Early nestling | Start Apr 15 | End Jun 30 | |||||||||
| Late nestling | Start Jun 15 | End Aug 15 | |||||||||
| Fledgling | Start Jul 15 | End Sep 15 |
Table 1: Bald Eagle Breeding Chronology Within Alaska. Dates represent the range of possible dates for a given activity. The nesting period, crucial for avoiding disturbance, is defined as March 1 through August 31 in Alaska.
Human activities that result in injury, decreased productivity, or nest abandonment are considered “take” under the Bald and Golden Eagle Protection Act. To mitigate disturbance, it is recommended to avoid certain activities during the nesting season (March 1 – August 31), maintain recommended distances from nests, and preserve natural vegetative buffers. These buffers help minimize visual and auditory impacts. The effectiveness of buffers depends on the landscape’s screening capabilities and the eagles’ historical tolerance to human activity. For temporary activities, seasonal restrictions are advised, while construction and habitat alteration projects require a combination of buffers and seasonal restrictions. For activities with the potential to disturb nesting eagles during the peak season, a permit from the Fish and Wildlife Service may be necessary.
Non-Breeding Period: Migration, Wintering, and Roosting
In the fall, many bald eagles in Alaska migrate to their wintering grounds as food sources become limited due to freezing conditions. While the exact wintering grounds for migratory eagles from Interior Alaska are not fully identified, it is believed they winter in Coastal Alaska and British Columbia. Eagles from Coastal Alaska may remain near their nest sites year-round, and immature eagles tend to wander more in search of food.
Wintering bald eagles are typically found near open water, where they prey on fish, marine invertebrates, and waterfowl, often scavenging on dead or vulnerable animals. Mammalian carrion also serves as an important food source in some areas. Key characteristics of winter habitat include an abundant food supply and suitable night roost sites.
During the night, wintering eagles often congregate in communal roost trees, selecting locations protected from the wind by vegetation or terrain to conserve energy. These sheltered sites help minimize thermal stress. Communal roosting may also facilitate food finding. These roost trees are often used year after year. While the precise locations of communal roosts in Alaska are not well-documented, activities that could disturb habitat should avoid known or suspected roosts.
Bald eagles are generally less sensitive to human disturbance during their migration and wintering periods compared to the breeding season. However, their reliance on specific wintering and roosting sites for feeding and shelter makes them vulnerable to permanent landscape changes that could eliminate these areas. Human activities near communal roost sites can also prevent eagles from feeding or sheltering, even without physical habitat alteration. Loss of these critical areas can harm bald eagles, particularly if alternative suitable areas are not readily available or if the eagles are in poor condition.
For comprehensive management guidance, consult the National Bald Eagle Management Guidelines. It’s important to note that the dates and sensitivity categories presented in the Alaskan context may differ from the National Guidelines due to Alaska’s unique climatic factors, vast geographic scale, and local expert opinions.
Bald Eagle Nest Atlas and Protection
The Bald and Golden Eagle Protection Act strictly prohibits the take of eagles, their nests, and eggs, whether directly through actions like shooting or indirectly through disturbance without a permit. To comply with this Act and protect nesting sites, bald eagle nest surveys have been conducted in Alaska since the 1960s. These surveys, historically conducted across various regions, were compiled in an effort to centralize information for land managers.
Modern technologies have enabled the creation of the Bald Eagle Nest Atlas, which displays documented bald eagle nests. This resource, maintained by the Fish and Wildlife Service and other collaborators, aims to make nesting information more accessible. However, the atlas is not a substitute for on-the-ground surveys to determine the presence, status, or exact location of active nests. Current nests and potential habitats may or may not align with the areas shown on the map. For inquiries about the map or nest locations, individuals are encouraged to contact Steve Lewis.
