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Northern eagles are larger than Southern eagles. Male Bald eagles’ weight may range from 6 to 9 pounds, with females’ weights usually 20 to 30 percent greater. Alaskan females reach up to 15 pounds. Florida males may weigh only 6 pounds. The average female Bald Eagle is 35 to 38 inches.
The wingspan varies from 6-8 feet.

The primary difference is that Bald Eagles belong to a group of “sea” eagles that live in or near aquatic environments and are piscivorous (fish eaters).

Golden Eagles belong to an entirely different group of eagles known as true or “booted” (legs with feathers versus scales) eagles and are upland eagles, meaning they are not near water. They hunt upland mammals mostly versus fish. These are just 2 of 59 species of eagles worldwide, but the only two which we have here in North America (except for another species that occasionally shows up in extreme southwest Alaska).

The “bald” eagle got its name from the Middle English word “balde” which means white-headed (not hairless!). “Golden” eagles likely got their name from the top and back of their head and neck, which are a beautiful golden color. – PN

Eagles adapt to the changes in temperature very efficiently. They have an under layer of fluffy down feathers under their outer feathers to insulate them from the cold. They “thermoregulate” (control their temperature) by panting with their mouth open or through heat loss through their unfeathered legs and feet. Babies are able to “thermoregulate” when they reach the age of 10 – 14 days old. Until then, the adult parents (usually the mother) sticks closely to the babies so they do not become too cold.

Females on the average are about 1/3 larger than males.

Two size measurements, beak depth and hallux (toe claw) length, show the greatest separation in sexes. These measurements can be used in the following equation: sex = (bill depth x 0.392) + (hallux length x 0.340) -27.694 (measurements in millimeters). If the answer is positive, the eagle is a female. If the answer is negative, the eagle is a male.

– PN

The life span of eagles in the wild is generally around 30 years. The longest that any Bald Eagle has been known to live in the wild is 39 years. In captivity, they may live over 50 years due to fewer hazards and veterinary care.

About 50 percent died during the first year due to their inexperience at meeting the dangers of living in the wild. After their first year, about 90 percent survive each year.

Eagles are thought to be able to reproduce throughout their lifespan, but little documentation is available. One eagle has been documented successfully raising young in her 26th year.

Bald Eagles have over 7,000 feathers. To see examples of the feathers, click here.

 The feathers of a bird are superbly crafted to form its aerodynamic shape and protect it from the challenges of water and weather. 

Feathers, like the scales on the feet, or the claws or the horny sheath of the bill are keratinous outgrowths of the skin, similar to our nails. Feathers grow out of skin follicles, just as human hair does. The skin tightly grips the feather cone at the follicle and tiny bunches of “feather” muscles in the skin at this site and between follicles holds the feathers and causes their movement. The skin surrounds and grows over the shaft.

A pin feather, sometimes called a “blood feather,” is a feather that is developing on a bird. It has a blood supply flowing through it, and if it is damaged, a bird can bleed heavily. As it grows longer, the blood supply is concentrated in only the base of the shaft. At this point, it is no longer called a “blood feather.” The feather comes out wrapped in a thin shaft of tissue, which will eventually split, which allows to unfurl and grow to its full size.

Eagles go through a molting experience with their feathers. The molting process is still not precisely understood. Prior to reaching sexual maturity at about age 5, we need to think of molts in terms of different plumages: young eagles go through four different plumages until they reach their sexually mature, adult plumage, which would be the fifth plumage type. These are (as described by Clark and Wheeler in Hawks of North America): Juvenile, White-belly I, White-belly II, and Adult transition plumages.

So, you might think, 5 years to sexual maturity, 5 plumages, one molt per year. Not exactly. Molt can be affected by a variety of biological and welfare factors (such as food supply, density of other eagles, and others), and not all molts are always complete molts.

Once they achieve their final “adult” plumage, it is likely that Bald Eagles molt their flight feathers just about every year. However, some evidence of molting can be seen at almost any time of the year.

This flight feather molt is not simultaneous; rather, matched flight feathers are generally lost at separate times, so the birds are never left flightless. – PN

A bird’s eggshell has thousands of tiny pores, which allow water and gas to pass through. Mammals like us get oxygen through an umbilicus, but developing birds receive oxygen and remove carbon dioxide through the egg shell. Gases, including oxygen, enter and leave the egg by diffusing through the pores in its shell, across the outer and inner shell membranes, and into the blood in the capillaries of a special tissue called the CAM, or chorioallantoic membrane. Condensation can form on eggshells if exposed to excessive humidity, which clogs shell pores and provides a vehicle for bacteria. The result? Fatal suffocation and/or contamination. Only the eagles know for sure, but I think they may have responded to the threat of rising humidity levels by leaving their eggs uncovered. Standing or leaving entirely allows fresh air to circulate over the eggs, dropping the humidity level and giving the developing embryos fresh air.”

Leucism is a genetic mutation that causes patches of white or overall faded or pale feathers to appear on a bird – and Bald Eagles are included. When this happens, melanin, or pigment, is prevented from being produced in parts of an animal’s body. In the case of birds, the pigment is absent from some feathers, which can result in weaker feather as well as a susceptibility to sunburn. Leucistic birds are rare, only occurring in about one in every 1,800 individuals, according to The Audubon Society Encyclopedia of North American Birds. Audubon goes on to say that with weakened wings and a susceptibility to sunburn, predators and parasite attacks, leukistic raptors usually don’t live long.

Links for images and more information are provided below:

The Cary Adventures (photo by Peter West Carey, 2018, showing an overall faded appearance in the eagle.)

10,000 Birds: A Leucistic Bald Eagle makes its appearance at the Winter Wings Festival in Klamath Falls, Oregon (several photos)