Part one of two about the bald eagle

Ben Franklin, the statesman, philosopher, naturalist, inventor and all around Renaissance Man, was not all that thrilled with the choice of the Bald Eagle as our national symbol, and seemed to prefer the wild turkey as a utilitarian symbol, which is uniquely American, and often spelled the difference between our wilderness forefathers eating or starving. In a letter to his daughter, Franklin said, in part…..

“For my own part I wish the Bald Eagle had not been chosen the Representative of our Country. He is a Bird of bad moral Character. He does not get his Living honestly. You may have seen him perched on some dead Tree near the River, where, too lazy to fish for himself, he watches the Labour of the Fishing Hawk (osprey); and when that diligent Bird has at length taken a Fish, and is bearing it to his Nest for the Support of his Mate and young Ones, the Bald Eagle pursues him and takes it from him. 

“With all this Injustice, he is never in good Case but like those among Men who live by Sharping & Robbing he is generally poor and often very lousy. Besides he is a rank Coward: The little King Bird not bigger than a Sparrow attacks him boldly and drives him out of the District. He is therefore by no means a proper Emblem for the brave and honest Cincinnati of America who have driven all the King birds from our Country . . . 

“I am on this account not displeased that the Figure is not known as a Bald Eagle, but looks more like a Turkey. For the Truth the Turkey is in Comparison a much more respectable Bird, and withal a true original Native of America . . . He is besides, though a little vain & silly, a Bird of Courage, and would not hesitate to attack a Grenadier of the British Guards who should presume to invade his Farm Yard with a red Coat on.”

Of course, these days we often call politicians “turkeys”, but I believe we have a different meaning in mind.

So….was Ben correct?

Well, yes and no. Bald eagles are opportunistic predators, and we have seen them steal fish from our local Adirondack ospreys, but that is fairly standard behavior for predators. Grizzlies will try to steal kills from wolves, but if there are more than two wolves, they will tease and harass the grizzly, until it gives up and leaves. Ravens will lead wolves to a winter killed-moose, but when the wolves are finished gorging, and are just lying around, the ravens will cover the carcass, but instead of eating, will cleverly steal and cache chunks of meat, hiding the cache from the wolves and other ravens, to assure a larger take, than if they simply stayed at the carcass and ate. 

Lions occasionally lose a kill to hyenas, so the rule seems to be, if you can accomplish it without too much risk, sometimes by sheer force of numbers or overwhelming size or strength disparity, it’s often easier to steal someone else’s prey than to secure your own, particularly when prey is not only scarce, but often dangerous, and your stomach is complaining. 

Eagles cluster where the opportunity for fishing and scavenging is greatest. When on the Kenai Penninsula in Alaska, on the way to Homer, there is an old Russian Village called Ninilchik, where the fishing boats dump unwanted catch in Cook Inlet, and there are always dozens of bald eagles on the beach there in the warmer months. Homer Spit and the Chilkat River north of Haines are other areas of large eagle gatherings.

General characteristics

The bald eagle, a relative of the white tailed eagle found in temperate areas of Europe and Asia, lives only in Canada, the U.S. and Northern Mexico, with eighty percent of bald eagles found in Alaska, and the density of eagles more pronounced along the west coast, particularly from Alaska down through British Columbia. Bald eagles are the largest North American raptor, averaging 6.5 to 14 pounds. They are rivaled in size only by the golden eagle, which averages about a pound less. One bald eagle, unfortunately shot in New York in the 1890s, weighed in at 18 pounds. 

All raptors display sexual dimorphism in size, with females being larger than males, and in the case of bald eagles, females average twenty five percent larger than males. We really don’t understand exactly why females are larger. My guess is the division of labor, with females spending more time on the nest than males, incubating eggs, and larger size is an advantage when defending the nest, while speed and agility are more important in hunting. Without a blood test, male raptors can’t be visually distinguished from females, and gender is usually guessed by size.

A large female measures about 36 inches in length, with a wingspan of 72 to 90 inches, and they can fly between 30 and 35 mph. They soar with a flat wing formation, and the wings are so powerful, they aid in swimming, as when an eagle tries to drag heavier prey through the water, pumping with those wings. As with other birds, eagle bones are hollow, making eagles lighter and better able to fly.

Eagles also conform to Bergmann’s Rule, which says that average individual size is determined by suitability of habitat, such that larger animals are more likely to retain body heat and survive in colder climate, thereby surviving to pass along genes for larger body size when breeding. Bald eagles in Alaska are considerably larger on average than those in Florida. Bald eagle migration follows similar patterns, with eagles in colder climates moving further south in winter than those in more temperate climates, most of whom remain in their territories

Immature eagles

Eagles have about 7,000 feathers which are moulted individually in sequence from head to tail over about six months, which explains the gradual streaky transformation of the head and tail from brown to white in immature eagles. During their first year, eagles grow larger feathers than their parents to provide greater lift and compensate for the lack of fully developed flight muscles. This is why first year eagles often look larger than their parents. Eagles make discordant, squeaky, gull like screams, which is why Hollywood movies substitute the more pleasing-to-the-ear cry of the red tailed hawk in scenes where eagles are featured.

Immature bald eagles are often confused with golden eagles, as the white head and tail feathers, signs of sexual maturity, don’t finish gradually showing through feather moulting until the fourth or fifth year, as the developing white streaking becomes solid white. Other signs which differentiate bald eagles from golden eagles are the fact that golden eagles have feathers up and down the legs, like trousers, and a lighter brown plumage, as immature bald eagles start out a darker brown before the white feathers begin appearing. 

We have a bald eagle at the Refuge who was shot as an immature eagle, but featured leucism, an excess of melanin, which led to lighter feather patterns to such an extent that we thought at first that it might be a young golden, until the head and tail streaking gradually showed it to be a bald eagle. Bald eagles also tend to have larger heads and beaks than goldens, and northern bald eagles have longer beaks than do southerly bald eagles. Immature bald eagles have darker beaks which gradually become solid yellow in maturity.

Strong senses

Like your fingernails, their beaks, talons and feathers are composed of keratin. Eagles are strong fliers with incredibly powerful talons. The general rule seems to be that an eagle can carry and fly with prey up to half its body weight. It’s talons exert a grip of ten times a human’s hand, so somewhere between 500 to 700 pounds per square inch, which is nearly equal to a grey wolf’s bite, and why eagle handlers use those thick padded gloves. The rear talon is often used to puncture and kill prey held immobilized by the three front talons, as the talons on the other foot and the beak are used to tear prey apart.

Bald eagles not only have sharper vision than we have, but a wider field of vision. As with other raptors, eagles have a nictitating membrane, an extra transparent eyelid which protects, moistens and cleans the eye. Eagles see in ultraviolet light, enabling them to detect urine trails of potential prey, just as UV enables some winter browsers like reindeer to spot lichen against the snow. Birds puff up their feathers for better insulation and to appear larger to predators.

Courting involves spectacular flight displays, with dives, swoops and aerial acrobatics in which eagles clutch each other’s talons and tumble through the air.

Photos courtesy of Steve Hall, Adirondack Wildlife Refuge