The bald eagle (Haliaeetus leucocephalus) is a large North American raptor, recognized as the national bird of the United States and Canada. This powerful bird of prey commands attention with its striking appearance and impressive size. Understanding the weight of an adult bald eagle provides insight into its biology as one of the continent’s largest flying creatures.
Average Weight and Typical Range
The mass of an adult bald eagle generally ranges from approximately 6.6 pounds (3.0 kilograms) to 13.9 pounds (6.3 kilograms). The average weight for the species hovers around 9.1 pounds (4.1 kilograms). These numbers represent an average across the entire North American range and do not account for individual differences.
A healthy adult’s weight is dynamic, influenced by recent feeding success and the time of year. Eagles often weigh the most during colder months when they spend more time foraging. Alaskan eagles frequently exceed the upper limit of the typical range, with some large females weighing over 15 pounds (7 kilograms).
Variation Based on Sex and Location
Weight variation is primarily explained by the bird’s sex and its geographic location. Bald eagles exhibit reverse sexual dimorphism, a trait common among raptors, where the female is noticeably larger and heavier than the male. Females typically weigh about 25% more than their male counterparts.
The average male bald eagle weighs around 9.0 pounds (4.1 kilograms), while the average female weighs 12.3 pounds (5.6 kilograms). This size difference gives the female an advantage during nesting, as her larger size is beneficial for incubation and protecting the nest. Larger females are also capable of subduing bigger prey, which is important for feeding their young.
Geographic location is another major determinant of mass, following Bergmann’s Rule. This rule suggests that animals in colder climates tend to be larger than those in warmer regions. Eagles found in the northern extremes of the range, such as in Alaska and Canada, are substantially heavier than those in the southern United States, like Florida or South Carolina.
Eagles from northern populations often belong to a larger subspecies, helping them conserve heat more efficiently. For example, eagles in South Carolina have an average mass of 7.2 pounds (3.27 kilograms), considerably less than the 10.7 pounds (4.79 kilograms) found in northern populations. A large male in the north could easily outweigh a small female from the south, illustrating the complexity of estimating size based on sex alone.
Comparing Weight to Wingspan and Body Length
The bald eagle’s relatively light weight is disproportionate to its overall dimensions, a characteristic adaptation for flight. The typical body length of an adult, measured from the beak tip to the tail end, spans from 28 to 40 inches (70 to 102 centimeters).
The most striking dimension is the wingspan, which provides the surface area needed to lift the bird’s mass during flight. An adult bald eagle’s wingspan typically measures between 5 feet 11 inches and 7 feet 7 inches (1.8 to 2.3 meters). The largest female eagles, particularly those in Alaska, can reach a wingspan of 8 feet (2.44 meters). These dimensions illustrate how the eagle’s body is engineered for aerial power, balancing a moderate mass with enormous wings for efficient soaring and hunting.