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 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

There are 59 species worldwide. Birdlife.org lists all the species with links to more information.

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