How Big Is a Bald Eagle? Size, Weight and Wingspan

Bald eagle size at a glance

The bald eagle is one of the two largest members of the hawk and eagle family (Accipitridae) in North America, alongside the golden eagle. These are the commonly cited ranges for wild adults:

The wingspan is the most impressive number. A large bald eagle soaring overhead spans wider than most adults are tall, and its broad, flat wings with “fingered” tips let it ride warm air currents for hours with few wingbeats.

For all that size, bald eagles are light. Their bones are thin-walled and hollow, so much of a bird that looks huge is actually feathers and air. Even the heaviest wild eagles rarely exceed 7 kg (15 lb).

Why female bald eagles are bigger than males

In bald eagles, as in most birds of prey, the female is the larger sex. This is called reversed sexual size dimorphism, because in most other birds and mammals the male is larger. Average figures from Alaska show the pattern clearly: adult females weighed about 5.35 kg (11.8 lb) and adult males about 4.23 kg (9.3 lb).

Scientists are still debating why. Leading ideas are that a larger female can produce eggs more easily, incubate and shield the chicks better and defend the nest against intruders, while a smaller, more agile male is an efficient hunter during the nesting season. Size differences may also help the pair avoid competing for exactly the same prey. Several of these explanations may be true at once.

In the field, the difference is useful. When a pair sits side by side on a branch or at the nest, the bigger, deeper-billed bird is almost always the female, even though both have identical plumage.

Why northern bald eagles are bigger

Bald eagle size follows Bergmann’s rule, the tendency for warm-blooded animals to be larger in colder climates. A large body loses heat more slowly relative to its mass, which helps in long northern winters.

The range of body size across the continent is wide:

• Southeastern United States: eagles from South Carolina averaged about 3.3 kg (7.2 lb) with a wingspan of about 1.88 m (6.2 ft), and Florida birds are similarly small.
• Interior and western United States: wintering eagles in Arizona averaged about 4.7 kg (10.4 lb), partly because birds are at their heaviest in winter.
• Alaska: the largest bald eagles in the world live here. Big females can exceed 7 kg (15 lb) and span about 2.4 m (8 ft).

Bill size varies even more than weight. Alaskan bald eagles can have bills nearly twice as long as those of eagles from Florida and the Gulf states. Traditionally the small southern birds and large northern birds were treated as two subspecies, but because sizes change gradually from south to north, many ornithologists see this as a smooth gradient rather than two distinct forms.

How big is a bald eagle compared with other raptors?

Here is how the bald eagle compares with other well-known birds of prey (wild adults, typical ranges):

The golden eagle is the bald eagle’s closest rival in North America. North American golden eagles average only about half a kilogram (1 lb) lighter, and their wings are slightly longer, so in practice the two are about the same size. Bald eagles tend to look bulkier because of their bigger heads and bills, while golden eagles have longer tails. See bald eagle vs golden eagle for how to tell them apart.

The world’s heaviest eagles are found elsewhere. The harpy eagle of Central and South American rainforests and Steller’s sea eagle of northeastern Asia, a close cousin of the bald eagle, both outweigh it on average. A red-tailed hawk, by comparison, weighs only around a quarter as much as a bald eagle. For the full ranking, see what is the largest eagle in the world?.

Size records and exaggerations

Reports of giant eagles should be treated with care. The heaviest reliable wild weights for bald eagles are around 7–7.5 kg (15–16.5 lb), all from Alaskan females. An old record of an 8.2 kg (18 lb) eagle shot in New York in 1876 is often repeated but cannot be checked.

Wingspan claims of 2.5 m (8 ft 2 in) or more for bald eagles are rare and usually unverified. Captive eagles can be heavier than wild ones because they are fed regularly and fly less, so zoo or rehabilitation weights are not a fair guide to wild birds.

A common myth is that a bald eagle can carry off a small deer or a large dog. In reality, a bald eagle can usually lift only around half its own weight, about 2–3 kg (4–7 lb), in normal flight. Heavier fish are often dragged or “rowed” across the water rather than lifted.

How fast do bald eagles grow?

Bald eagle chicks hatch weighing only a few ounces and grow faster than almost any other North American bird, gaining up to about 170 g (6 oz) a day at their peak. Young eagles reach roughly adult size at about 10 to 12 weeks old, when they leave the nest.

Juveniles in their first year can look bigger than their parents. Their flight feathers are longer than an adult’s, which gives them a larger wingspan and a longer tail for a few years while they learn to fly and hunt.