History of the Bald Eagle
Before European settlers first sailed to America’s shores, bald eagles may have numbered half a million. They existed along the Atlantic from Labrador to the tip of south Florida, and along the Pacific from Baja California to Alaska. They inhabited every large river and concentration of lakes within North America. They nested in forty-five of the lower forty-eight states. One researcher estimated an eagle nest for every mile of shore along Chesapeake Bay. They congregated on th
There is no single cause for the decline in the bald eagle population. When Europeans first arrived on this continent, bald eagles were fairly common. As the human population grew, the eagle population declined. The food supplies for eagles decreased, because the people hunted and fished over a broad area. Essentially, eagles and humans competed for the same food, and humans, with weapons at their disposal, had the adddvantage. As the human population expanded westward, the natural habitat of the eagles was destroyed, leaving them fewer places to nest and hunt, which caused the population of bald eagles to decline sharply by the late 1800s.
By the 1930s, people beeecame aware of the diminishing bald eagle population, and in 1940 the Bald Eagle Act was passed. This reduced the harassment by humans, and eagle populations began to recover. However, at the same time DDT and other pesticides began to be widely used. Pesticides sprayed on plants were eaten by small animals, which were later consumed by birds of prey. The DDT poison harmed both the adult birds and the eggs that they laid. The egg shells became too thin to with stand the incubation period, and were often crushed. Eggs that were not crushed during incubation often did not hatch, due to high levels of DDT and its derivatives. Large quantities of DDT were discovered in the fatty tissues and gooonads of dead bald eagles, which may have caused them to become infertile.
More than 100,000 bald eagles were killed in Alaska from 1917 to 1953. Alaskan salmon fisherman feared they were a threat to the salmon population.
Public awareness increased, and many states placed the bald eagle on their lists of endangered species in the 1960s and early 1970s. Many dedicated individuals and groups worked to make the conservation of eagles a national issue.
Bald eagles were officially declared an endangered species in 1967 in allll areas of the United States south of the 40th parallel, under a law that preceded the Endangered Species Act of 1973. The Endangered Species Act was signed into law in 1973 by President Richard Nixon. This landmark legislation is regarded as one of the most comprehensive and important wildlife conservation laws in the world. Federal and state government agencies, along with private organizations, successfully sought to alert the public about the eagle’s plight and to protect its habitat. On July 4, 1976, the US Fish and Wildlife Service officially listed the bald eagle as a national endangered species.
Until 1995, the bald eagle had been listed as endangered under the Endangered Species Act in 43 of the 48 lower states, and listed as threatened in Wisconsin, Minnesota, Michigan, Washington and Oregon. In July of 1995, the US Fish and Wildlife Service upgraded the status of bald eagles in the lower 48 states to threaten.
Only a handful of species have fought their way back from the United States’ endangered species list. The California gray whale, the American alligator, and the bald eagle are a few. Once endangered in all of the lower 48 states, the bald eagle’s status was upgraded to “threatened” in 1995, two decades after the banning of DDT and the passing of laws to protect both eagles and their nesting trees.
About half of the world’s 70,000 bald eagles live in Alaska. Combined with British Columbia’s population of about 20,000, the northwest coast of North America is by far their greatest stronghold. They flourish here in part because the salmon. Dead or dying fish are an important food source for all bald eagles.
Causes of death to the bald eagle are:
1. Fatal gun shot wounds by careless and ignorant recreational hunters, malevolent people, and those hunting them for their feathers and talons to sell on the black market.
2. Electrocution from taking off and landing on power poles when their large wings bridge two wires, resulting in fatal burns or heart failure.
3. Lead poisoning from eating wounded deer, ducks, and other game which eluded the hunter and later died. Three pellets can kill an eagle.
4. Less adept at hunting, young eagles are more likely to eat carrion, and possibly ingest poisoned meat used to bait wolves and coyotes.
5. Collisions with vehicles.
6. Starvation where the food is scarce. Up to half of them starve to death their first winter, due to lack of hunting skills.
7. If an eagle ends up in the water due to misjudgment of altitude or snagging a large fish, there’s a danger they may die of exposure.
Bald Eagle Body Description
Color. Both male and female adult bald eagles have a blackish-brown back and breast; a white head, neck, and tail; and yellow feet and bill.
Juvenile bald eagles are a mixture of brown and white; with a black bill in young birds. The adult plumage develops when they’re sexually mature, at about 4 or 5 years of age.
The bald eagle is the only eagle confined to North America, and there are no other large black birds in North America with white heads and tails.
Habitat. Bald eagles live along the coast and on major lakes and rivers where they feed mainly on fish.
Longevity. Wild bald eagles may live as long as thirty years, but the average lifespan is probably about fifteen to twenty years.
Body Temperature. 38.8 degrees Celsius.
Tolerance to cold temperatures. A bald eagle’s skin is protected by feathers lined with down. The feet are cold resistance because they are mostly tendon. The outside of the bill is mostly nonliving material, with little blood supply.
Eagles sit at the top of the food chain, making them more vulnerable to toxic chemicals in the environment, since each link in the food chain tends to concentrate chemicals from the lower link.
Fidelity. Once paired, bald eagles remain together until one dies, the survivor will not hesitate to accept a new mate.
Voice. Shrill, high pitched, and twittering are common descriptions used for bald eagle vocalizations. Eagles do not have vocal cords. Sound is produced in the syrinx, a bony chamber located where the trachea divides to go to the lungs. Bald eagle calls may be a way of reinforcing the bond between the male and female, and to warn other eagles and predators that an area is defended.
Skeleton. It weighs about 250 to 300 grams, and is only 5 or 6 percent of its total weight. The feathers weigh twice that much. Eagle bones are light, because they are hollow. The beak, talons, and feathers are made of keratin.
The wings and soaring. An eagle’s wings are long and broad, making them effective for soaring. To help reduce turbulence as air passes over the end of the wing, the tips of the feathers at the end of the wings are tapered so that when the eagle fully extends its wings, the tips are widely separated.
To help them soar, eagles use thermals, which are rising currents of warm air and updrafts generated by terrain, such as valley edges or mountain slopes. Soaring is accomplished with very little wing-flapping, enabling them to conserve energy. Long-distance migration flights are accomplished by climbing high in a thermal, then gliding downward to catch the next thermal, where the process is repeated.
Bald eagles can fly to an altitude of 10,000 feet. During level flight, a bald eagle can achieve speeds of about 60 to 70 km/h.
The tail. is very important for flight and maneuvering. While the bald eagle is soaring or gliding in flight, the tail feathers are spread, in order to attain the largest surface area and increase the effect of thermals and updrafts. The tail also helps to brake the eagle when landing and assists in stabilization during a controlled dive or swoop toward prey. The strength of the feathers and the follicles holding the feathers is quite impressive, while watching the tail move back and forth and up and down during maneuvers.
Bald eagles have 7,000 feathers. Eagle feathers are lightweight yet extremely strong, hollow yet highly flexible. They protect the bird from the cold as well as the heat of the sun, by trapping layers of air. To maintain its body temperature an eagle simply changes the position of its feathers. While an eagle suns itself on a cold morning, it ruffles and rotates its feathers so that the air pockets are either opened to the air or drawn together to reduce the insulating effect. Feathers also provide waterproofing and protection, and are crucial for flight.
Feather structure makes pliability possible. Overlapping feathers can form a dense covering, which the birds can open or close at will. The bald eagle has several layers of feathers, each serving a different function. Under the outer layer of feathers is an inner layer of down or smaller feathers. The inter locking of feathers is an astonishing design of nature.
The feathers enable eagles to live in extremely cold environments. Eagles do not have to migrate to warmer areas each year to fulfill temperature requirements; they migrate to available food supplies.
A lone eagle feather is believed to convey great power. North American Indians incorporated the eagle’s primaries and tail feathers into their ceremonies and legends.
Respiratory system. Eagles have external nares opening on both sides of the bill. A bald eagle never reaches speeds that would interfere with normal breathing. The eagle’s lungs and air sac system is adequate for its size. Air moves in through the lungs and on into the air sacs before moving back through the lungs and out again. Air passes through the lungs twice with each breathing cycle – twice that of mammals.
Talons. Talons are important tools for hunting and defense. Eagles kill their prey by penetrating its flesh with their talons.
Eagles can open and close their talons at will. If an eagle is dragged into the water by a fish too large for the eagle to lift, it is because the eagle refuses to release it. In some cases this is due to hunger. An eagle might drown during the encounter with the fish or if it’s unable to swim far enough to reach shore.
Beak. The hook at the tip is used for tearing. Behind the hook, the upper mandible, the edge sharp enough to slice tough skin, over laps the lower, creating a scissors effect. A bald eagle’s beak is a strong weapon, but is also delicate enough to groom a mate’s feathers or feed a small portion of food to a newly hatched chick.
The beak of a female eagle is deeper (distance from top to chin) than the beak of a male.
The beak and talons grow continuously, because they are made of keratin, the same substance as our hair and fingernails. The beak of a captive eagle is not warn down naturally, so must be trimmed annually.
All eagles are renowned for their excellent eyesight, and the bald eagle is no exception. They have two foveae, or centers of focus, that allow the birds to see both forward and to the side at the same time. Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding, or in flapping flight. This is quite an extraordinary feat, since most fish are counter-shaded, meaning they are darker on top and thus harder to see from above. Fishermen can confirm how difficult it is to see a fish just beneath the surface of the water from only a short distance away.
Young bald eagles have been known to make mistakes, such as attacking objects like plastic bottles floating on or just below the surface of the water. Bald eagles will locate and catch dead fish much more rapidly and efficiently than live fish, because dead fish float with their light underside up, making them easier to see.
Eagles have eyelids that close during sleep. For blinking, they also have an inner eyelid called a nictitating membrane. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while it is over the eye.
Eagles, like all birds, have color vision. An eagle’s eye is almost as large as a human’s, but its sharpness is at least four times that of a person with perfect vision. The eagle can probably identify a rabbit moving almost a mile away. That means that an eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles from a fixed position.
Eagles are not distinguished for their hearing, but this does not mean that they have poor hearing. Diurnal (active by day) birds of prey like hawks and eagles use their hearing to locate prey or other birds, but the sharpness is not as essential as in some owls, which can locate prey in the dark only by their sound.
A Bald Eagle’s Diet and Feeding Habits
The bald eagle is a member of the sea and fish eagle group. Its closest relatives, similar in appearance and habit, are found in Africa and Asia. Even though they are fish eaters, they will take whatever prey is available and easiest to obtain. Bald eagles which live along the coast and on major lakes and rivers feed mainly on fish. Bald eagles fish in both fresh and salt water.
Eagles sit at the top of the food chain, making them more vulnerable to toxic chemicals in the environment, since each link in the food chain tends to concentrate chemicals from the lower link. Because of their size, they have few enemies and require a large hunting area.
A bald eagle’s lifting power is about 4 pounds. They do not generally feed on chickens or other domestic livestock, but they will make use of available food sources. Bald eagles will take advantage of carrion (dead and decaying flesh). Because of its scavanger image, some people dislike the bald eagle. Other people do not care for powerful and aggressive birds. Still other people object merely on the grounds that it is a bird of prey, which kills other animals for food.
Once an eagle spots a fish swimming or floating near the surface of the water, it approaches its prey in a shallow glide and snatches the fish out of the water with a quick swipe of its talons. Eagles can open and close their talons at will. If an eagle is dragged into the water by a fish too large for the eagle to lift, it is because the eagle refuses to release it. In some cases this is due to hunger. An eagle might drown during the encounter with the fish or if it’s unable to swim far enough to reach shore. The eagle can not fly again until it’s out of the water, so it uses its large wings to swim. The eagle is a strong swimmer, but if the water is very cold, it may be overcome by hypothermia.
The hunting area or home range patrolled by a bald eagle varies from 1,700 to 10,000 acres. Home ranges are smaller where food is present in great quantity.
Because of the energy expended during hunting, an eagle has to spend a lot of time resting quietly. It’s estimated that only one out of eighteen attacks are successful.
Though not as fast as falcons, bald eagles are fast fliers. When diving, where lift is less important than reaching drag, the eagle pulls in its wings to minimize their surface area.
Bald eagles have been seen hunting in pairs.
An eagle protects its food by partially opening its wings, or tenting.
An eagle can consume one pound of fish in about four minutes. The eagle holds its prey with one talon, holds onto its perch with the other, then tears off each bite with its beak.
The bald eagle steals food from other bald eagles as well as other species. Chasing another raptor is usually enough to persuade it to drop its kill, but occasionally bald eagles will attack.
Bald eagles do not have to eat every day. But if the bird goes too long without food, it may not be able to hunt effectively in order to survive.
Eagles have an out pouching of the esophagus, called a crop, where they can store food when the stomach is full. The crop also separates indigestible substances, such as feathers, fur, and scales from the meat. The indigestible substance is mixed with mucus and formed into a mass. After the meal, the eagle eventually regurgitates the mass as a casting.
For a scavenger like the bald eagle, the carcass of a seal is an unexpected large food supply. Rich with fat and protein, the seal’s body will feed a group of eagles for days. Though many calories will be obtained, they will be lost in fighting over the food.