Despite Benjamin Franklin’s efforts to enshrine the Wild Turkey as our national symbol, the Bald Eagle was selected instead. The large, majestic adult Bald Eagle, dark in color save for the pure white head and tail, is familiar even to non birders. After a brush with extinction following the widespread use of the chlorinated hydrocarbon pesticide DDT, the Bald Eagle has made a remarkable comeback, due mostly to the banning of DDT, but also as a result of successful reintroduction efforts. Today, among the lower 48 U.S. states, only two states do not currently have nesting Bald Eagles. Nesting populations in the southern U.S. are supplemented in winter by a large influx of northern birds abandoning frozen lakes and rivers that make the Bald Eagle’s fishing habits impossible during several months of the year. Observers along major river systems such as the Missouri and Mississippi, and observers in southern states with large numbers of impoundments such as Oklahoma, have no trouble seeing Bald Eagles, especially during the winter months.
Another species of eagle, the Golden Eagle, is actually more closely related to the buteo hawks than to the Bald Eagle, and is also quite widespread in winter. Though rare in the southeastern U.S., the Golden Eagle can potentially be seen almost anywhere in the lower 48 states during the winter months, the same time at which Bald Eagles are most numerous there. While adult Bald Eagles are quite distinctive and pose little in the way of identification difficulties, both species of eagles have distinctive transitional plumages over a period of several years before maturity is reached, something that also occurs in gulls and a few other species. It is these younger birds that may cause birders to take a second look when a large raptor with the size, bearing, and behavior of an eagle flies overhead.
Plumage features to note on an eagle other than an adult Bald include the amount and distribution of white in the tail and the undersides of the wings. Juvenile (first winter) Golden Eagles typically have distinctive, discrete white patches near the outer ends of the wings, dark axillaries and coverts, and a white-based tail with dark terminal band. First winter Bald Eagles have widespread white mottling on the undersides of the wings, especially on the axillaries and coverts, while the belly is brown. The underside of the tail is often largely white, though less pure and pronounced white than in Golden Eagles. Second through forth year Golden Eagles look much more like adult Golden Eagles, i.e., they have relatively little white in the wings and tail. Second winter Bald Eagles have even more extensive white on the undersides than first winter birds, with the white not being limited to the wings and tail but also including the belly. Over the next two to three years, they gradually attain the dark body and wings, and white head and tail, of mature Bald Eagles. The golden nape of Golden Eagles is present in all age groups, and is another useful plumage feature to look for.
Differences in shape can also be useful in distinguishing Bald and Golden Eagles, even when lighting is bad or the bird is distant. The head of a Bald Eagle in flight appears rather large, while Golden Eagles appear small-headed by comparison. The wings of Bald Eagles appear somewhat straighter and narrower than those of Golden Eagles, which have broader secondaries creating a “bulge” in the rear edge of the wings.
Finally, though not definitive given the wide ranging nature of these large raptors, Bald Eagles are primarily fish eaters and are usually found near large bodies of water, while Golden Eagles are primarily mammal eaters, and are usually found in open country. Careful scrutiny of each eagle in winter may result in an unexpected addition to the day’s bird list.
Thanks to Dan Reinken for this information.