Back

BALD EAGLES

History of Bald Eagles

On June 20, 1782, The Bald Eagle, or American Eagle, became the National Emblem of the United States by the Second Continental Congress because of its long life, great strength, majestic looks, and belief that it was unique to North America. The wild turkey was runner-up. The Great Seal of the United States was adopted at this time and shows a wide-spread eagle, faced front, breast covered with a shield of thirteen perpendicular red and white stripes, with a blue field with the same number of stars; right talon holding an olive branch; left talon holding a bundle of thirteen arrows; and beak carrying a scroll with the motto: E Pluribus Unum. The eagle appears in many state seals, on gold and silver coinage, and used for decorative patriotic purposes.

Before Europeans settled in America, there may have been about 500,000 bald eagles. As the human population grew, the eagle population declined, partly because they were competing for the same food and humans had weapons to their advantage. There was a sharp decline in the late 1800s. At this time, European settlers spun tales of eagles carrying away full-grown sheep, and even human babies, and they viewed them as potential livestock predators. This is not possible because the lifting power of an adult eagle is no more than about 4 or 5 pounds. Their scavenger image, powerfulness, and aggressiveness contribute to the negative image some people have of them.

In 1918, they received protection under the Migratory Bird Treaty Act of 1918. In 1940, the Bald Eagle Act was passed by Congress. They began replenishing until DDT and other pesticides became widely used in the 1950s and 60s after World War II, which affected them because they would eat the poisoned small animals. The DDT-infected eagles laid eggs with too-thin shells that could not last the incubation period because they were not able to release calcium into the egg shells. In Alaska, more than 100,00 bald eagles were killed between 1917 to 1953 because fishermen feared they were a threat to salmon. The population dropped along with other predatory birds like the peregrine falcon and brown pelican.

In the 1960s and early 70s, they were placed on the endangered species list. Rachel Carson warned about the long-term effects of pesticide misuse in her 1962 book Silent Spring. In 1967, they were officially declared endangered under a law that preceded the Endangered Species Act of 1973. DDT was outlawed in the United States in 1972. On July 4, 1976, the U.S. Fish and Wildlife Service officially added it to their national list. In the early 1980s, the National Wildlife Federation was able to get the U.S. Fish and Wildlife Service to nationally ban lead shot in waterfowl hunting. By 1988, bald eagles were reproducing successfully in the wild and the federal reintroduction program was discontinued. In July 1995, their endangered states was added to Wisconsin, Minnesota, Michigan, Washington, and Oregon, where previously it had been 43 of the 48 lower states. In 1999, there was a proposal to remove the bald eagle from the federal list of endangered and threatened species.

Other historical significance of the eagle include the Egyptian hieroglyphic of an eagle that is symbolic of the free-soaring soul of man, adaptation of the eagle symbol by Phoenicians for the letter a, and American Indian custom of wearing eagle feathers as badges of rank and courage. Sacred among Native Americans, they fear being cursed if an eagle feather touches the ground. Of the 500 tribes, most view the eagle as a connection between them and the Creator. They are featured at the top of the center pole during the sun dancean important religious ceremony. Even though possession of eagles and/or eagle parts is illegal, Native Americans can obtain a permit for receipt of those killed by human causes.

What Do Bald Eagles Look Like?

Physical Descriptions

Haliaeetus leucocephalus, the bald eagles scientific name translates: a sea (halo) eagle (aeetos) with a white (leukos) head. Its name comes from the old English word, balde, which meant white-faced. In the past, the word bald meant white, not hairless. Adult bald eagles have a blackish-brown back and breast; white head, neck, and tail; and yellow feet and bill. Their feet are not feathered like golden eagles. There are no other large black birds in North America with white heads and tails. The sex of a bald eagle can be determined by its beak. Females have deeper ones.

Newly hatched Bald Eaglets are light grey. They turn dark brown about 12 weeks of age, before they leave the nest. At age 3 and 4, they have mottled brown and white feathers under their wings and on their head, tail, and breast, along with black bills, and are easily confused with the golden eagle. At 4 to 5 years of age, when they are sexually mature, their distinct plumagewhite head and tail feathersappear and their dark brown eyes turn yellow.

One of the largest birds in North American, they are about 29 to 42 long, weigh 7 to 15 pounds, and can have a wing span of 6 to 8 feet. Females and northern eagles are larger, with females ranging from 35 to 37 with a wingspan from 79 to 90. The golden eagle is larger than the bald eagle in height and wingspan. Although male eagles are smaller, they are quicker and more agile, which is ideal for catching prey. The females larger size is good for incubating eggs and brooding the young chicks. She can use her body to shelter them from cold, soaking rains or hot sun.

Long and broad wings are effective for soaring, which requires very little wing-flapping and allows them to conserve energy. Their feather tips at the end of their wings are tapered and this helps reduce turbulence as air passes over the end of the wing. While they can swoop down to seize prey in their talons, they can only lift about half their weight in flight. If a fish is too heavy, they can swim ashore using their wings as paddles. Their flight speed can range between 65 miles per hour to 200 miles per hour depending on whether or not it is a level flight or a dive. They can soar for hours using rising warm air wind currents and thermal updrafts generated by terrain like valley edges or mountain slopes. They can fly to altitudes of 10,000 feet or more. For long-distance migration flights, they climb high in a thermal, then glide downward to catch the next one. A kettle of eagles is when several soar in a thermal together.

Eagle tails are very important for flight and maneuvering by helping eagles soar or glide in flight, brake when landing, and stabilize during a controlled dive or swoop. Their skeletons weigh around a .5 pounds and are only 5 to 6 percent of their total body weight. Their feathers weigh twice that much. Their hollow bones are light and their beak, talons, and feathers are made of keratin, the same substance that human hair and fingernails are made of. Since their beak and talons grow continuously because of this fact, the beaks of captive eagles have to be trimmed annually without the benefit of natures wearing down of it. The hook at the tip of their beaks is used for tearing and the upper mandible behind it is sharp enough to slice tough skin. Their talons are important for hunting and defense.

Eagle body temperature rests at 102 degrees Fahrenheit. Their skin is protected by down-lined feathers that aid in their tolerance of cold weather, along with their cold resistant feet made of tendons, and cold resistant bills that are made of nonliving material with little blood flow. Eagles have 7,000 lighweight feathers that are very strong and flexible, but hollow. The feathers, which have an interlocking design, protect from cold and heat by trapping layers of air and provide waterproofing and protection in rain that are crucial for flight. The different layers of feathers each serve their own purpose. Eagles do not migrate to warmer areas because of extreme cold, they move for available food supplies.

Their respiratory system consists of external nares opening on both sides of their bills, an air sac system, and lungs that air pass through twice with each breathing cycle (twice that of mammals).

Eagles do not have vocal cords. Their shrill, high-pitched, and twittering sounds are made by their syrinx. Their bird calls reinforce male/female bonds and warn other eagles and predators that an area is under their defense.

Renowned for their superb vision, they have two centers of focus that allows them to see both forward and to the side simultaneously. They can sight fish from several hundred feet above while in flight, which is remarkable because fish tend to be counter-shaded (darker on top) and harder to see from above. Their eyelids close when they are sleeping and for blinking they have a translucent inner eyelid that slides across the eye from front to back every three to four seconds that wipes dirt and dust from the cornea, while still allowing the eagle to see. Eagles have color vision like all birds and although their eye is almost the size of humans, they are at least four times sharper.

Diurnal (active by day) birds of prey like hawks and eagles use their hearing to locate prey or other birds, but it is not as essential, therefore, not as sharp as that of an owl who can find prey in the dark by sound.

Where Do Bald Eagles Live?

Bald eagles resides in North America, from Alaska and Canada to northern Mexico near swamps, lakes, oceans and rivers where there are lots of fish, clean waters, and tall trees for nesting and roosting. They live strictly in North America and every state except for Hawaii. The northwest coast of North America is where the flourish most, partly because of the salmondead or dying fish are an important part of their food supply. In 1996, more than 40 were observed wintering along the Columbia River north of the Hanford townsite. Thousands live in Alaska and other parts of the Pacific Northwest, the Great Lakes region, and Chesapeake Bay. They also inhabit Florida and along Atlantic coastline. They thrive in quiet isolation.

What Do Bald Eagles Eat?

Food Sources and Hunting Habits

Raptors (predatory birds), bald eagles are at the top of the food chain and fish in both fresh and salt water. They feed on fish, small animals like ducks, coots, muskrats, turtles, rabbits, and snakes and carrion (dead animals) occasionally. Fish account for 90% of their diet; however, they will prey on whatever is available and easiest to get. It takes them about four minutes to eat one pound of fish. While catching their prey, they rarely enter the water, they snatch the fish from the surface with their talons. They also steal fish from ospreys which are smaller. Historically, ranchers and farmers shot and killed them in large numbers because they were grouped with raptors that killed chickens, lambs, and other domestic livestock.

They have few enemies because of their size and require a large hunting area. Their lifting power is about 4 pounds. Bald eagles approach their prey in a shallow glide, then snatch with a quick swipe of their talons that have a special locking mechanism that instantly closes when they touch prey and cannot be opened again until the bird pushes down on a solid surface. They are strong swimmers and can plunge into water while trying to catch a fish; however, may experience hypothermia if the water is too cold.

Bald eagles spend a lot of time resting quietly because they use an abundance of energy while hunting. Only one out of 18 attacks are successful. They protect their food by tenting with partially opened wings. While eating, they hold their catch with one talon, hold onto their perch with the other, and tear off bites with their beaks. They store food in their crop when they are full and regurgitate indigestible things like feathers, fur, and scales.

Food is not required daily for their survival; however, if they go too long without it, it hinders an effective hunt.

Breeding Cycles of Bald Eagles

Mating and Nesting

Monogamous, they mate for life until the death of one mate. Eyries, large nests lined with twigs, soft mosses, grasses, and feathers, about 2 feet deep and 5 feet wide that they build at the top of sturdy trees grow larger (about 10 feet wide and several tons) when they add new nesting materials each year while repairing before breeding. Nest shapes are determined by whether or not sticks are placed in deep, vertical forks (conical nests), ground or level branches (disk-shaped nests), or tree trunks that suddenly branch into smaller upright branches (bowl-shaped nests). They usually nest in trees, but sometimes on cliffs, and often within 100 miles of where they hatched, staying in the same neighborhood as their parents. Territorial while nesting, they will attack other eagles within their area. The nesting cycle lasts about 20 weeks.

Bald eagles are sexually mature around four or five years old and dedicate themselves to finding a mate to raise offspring with. Mating season varies by region. Eagles do not copulate in the air like some believe because pairs have been seen whirling through the air with talons locked in a form of courtship or ritualized battle. Breeding may not occur annually for some eagles by voluntary choice. They may instinctively realize bad timing because of weather, nesting site availability, or food.

In the springtime, five to ten days after copulation, the female lays 1 to 3 speckled off-white or buff colored goose-sized eggs a few days apart. During incubation, male bald eagles bring green sprigs of conifer branches to the nest, possibly for deodorizing or shade. Both parents share the duties: hunting, egg incubation, nest watch, eaglet feeding, and eaglet brooding; however, the female does most of the nesting. One parent is always on the nest to keep eggs warm and safe from squirrels, ravens, and gulls. The male will often eat the head of fish and bring the remains to the nest. He shares brooding duties so that the female can stretch, defecate, bathe, preen, and hunt on her own. Eagles need privacy and quiet to breed. If they are disturbed, they may abandon their nest. People should use binoculars and spotting scopes for viewing at a distance.

Eaglets hatch after an incubation period of about 35-38 days in the order they were laid, by using their egg tooth, a pointed bump on the top of the beak, to break the shell. Hatching can take half a day to two days. Newly hatched chicks measure 4 to 5, with soft, grayish-white bodies, wobbly legs, and partially closed eyes. When two chicks survive, the older one may kill the smaller one and the parents will not stop them. Parents feed them by shredding pieces of meat with their beaks and while moving around in the nest they wall with their talons balled into fists to avoid harming their young. Eaglets diets consist of fish with supplements of water fowl or birds.

Eaglets grow a pound every four or five days and can hold their heads up for feeding around two weeks. At three weeks, they are one foot high and their feet and beaks are near adult size. At six weeks, they are about the size of their parents. They are full size at about 12 weeks and learn to fly. When their wing and tail feathers are fully developed, they can leave the nest. Before first flights, which may be to the nearest branch above the nest, eaglets do vigorous exercise and flapping. They will lift off by facing into prevailing winds and flapping or may be forced to fly by parents.

About 40% survive their first flight and only about half survive their first year for various reasons including starvation and the inability to recognize poisoned food.

Migration Patterns of Bald Eagles

Bald eagles migrate when northern lakes and rivers freeze. They usually go to the coast or large rivers near dams where the water remains open. Their flight patterns are determined by wind currents. They migrate through the Columbia Basin. Some spend their winters along the Hanford Reach of the Columbia River, while others frequent the Yakima River. Those that go to Washington continue on to Alaska or British Columbia to hatch their chicks. Newly fledged eagles instinctively migrate and know when and where to travel.

In the fall, they migrate slowly south for sufficient food. Sometimes a week may have passed before they leave an area. In the spring, they migrate quickly north to nest. They fly during the day at 30 miles per hour and tend to flock in groups. A stream may be 20 to 30 miles long, with birds spread out about a half mile apart. Not all bald eagles migrate. For instance, those in Florida may remain there year-round.

They only travel as far as they need to for food, unlike a robin or bluebird migration.

Normal Lifespan and Causes of Deaths for Bald Eagles

They live to 30 to 40 years in the wild, and longer in captivity. The average lifespan is 15 to 20 years. A captive eagle lived to be at least 48 years old in West Stephentown, New York. Bald eagles die prematurely for various reasons. They are fatally shot for sport or money, electrocuted when they take off or land on power poles and their large wings bridge two wires, lead poisoned from feasting on wounded deer, ducks and other game shot by hunters, killed by eating poisoned meat used to bait wolves and coyotes, killed by ingestion of lead shot and lead fishing sinkers, killed by by mercury, PCBs, dioxins and other chemicals that accumulate in fish, killed by colliding with vehicles, and starved to death when their food is scarce. Habitat destruction through deforestation and flooding of bottomland hardwood ecosystems, as well as human disturbance of nest sites threaten their existence.

Patriotic Poetry The Eagle as National Emblem

The American Eagle

Bird of Columbia! well art thou

An emblem of our native land;

With unblenched front and noble brow,

Among the nations doomed to stand;

Proud, like her mighty mountain woods;

Like her own rivers wandering free;

And sending forth from hills and floods

The joyous shout of liberty!

Like thee, majestic bird! like thee,

She stands in unbought majesty,

With spreading wings, untired and strong,

That dares a soaring far and long,

That mounts aloft, nor looks below

And will not quail, though tempests blow.

The admiration of earth,

In grand simplicity she stands;

Like thee, the storms beheld her birth,

And she was nursed by ragged hands;

But, pasted the fierce and furious war,

Her rising fame new glory brings,

For kings and nobles come from far

To seek the shelter of her wings.

And like thee, rider of the cloud,

She mounts the heavens, serene and proud,

Great in her pure and noble fame,

Great in her spotless champion's name,

And destined in her day to be Mighty as Rome, more nobly free.

---C. W. Thompson

The Eagle

He clasps the crag with crooked hands;

Close to the sun in lonely lands,

Ring'd with the azure world, he stands.

The wrinkled sea beneath him crawls;

He watches from his mountain walls,

And like a thunderbolt he falls.

---Alfred Tennyson

The Eagle, Our National Emblem

   On the backs of our gold coins, the silver dollar, the half dollar and the quarter, we see an eagle with outspread wings.
   On the Great Seal of the United States and in many places which are exponents of our nation's authority we see the same emblem.
    The eagle represents freedom. Living as he does on the tops of lofty mountains, amid the solitary grandeur of Nature, he has unlimited freedom, whether with strong pinions he sweeps into the valleys below, or upward into the boundless spaces beyond.
    It is said the eagle was used as a national emblem because, at one of the first battles of the Revolution (which occurred early in the morning) the noise of the struggle awoke the sleeping eagles on the heights and they flew from their nests and circled about over the heads of the fighting men, all the while giving vent to their raucous cries. "They are shrieking for Freedom," said the patriots.
   Thus the eagle, full of the boundless spirit of freedom, living above the valleys, strong and powerful in his might, has become the national emblem of a country that offers freedom in word and thought and an opportunity for a full and free expansion into the boundless space of the future.

--Maude M. Grant

Sources:

http://www.eagles.org/

http://www.baldeagleinfo.com/

http://www.nu.com/eagles/

http://www.kenyabirds.org.uk/fish_eagles.htm

http://www.naturia.per.sg/buloh/birds/Haliaeetus_leucogaster.htm

http://www.peregrinefund.org/Explore_Raptors/eagles/goldeagl.html

http://www.hawk-conservancy.org/priors/booted.shtml

http://www.safaricamlive.com/Encyclopedia/birds/eagles/Brown%20Snake%20Eagle%20Info.htm

http://www.cnn.com/2000/NATURE/08/14/philippine.eagles/

http://www.pnl.gov/pals/resource_cards/Bald_Eagles.stm