Bald Eagle

The bald eagle (Haliaeetus leucocephalus), America's national bird, is the only eagle unique to North America. The bald eagle's scientific name signifies a sea (halo) eagle (aeetos) with a white (leukos) head. At one time, the word "bald" meant "white," not hairless. Bald eagles are found throughout most of North America, from Alaska and Canada to northern Mexico. 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 for bald eagles. They flourish here in part because of the salmon. Dead or dying fish are an important food source for all bald eagles.

Eagles are a member of the Accipitridae family; which also includes hawks, kites, and old-world vultures.
   Scientists loosely divide eagles into four groups based on their physical characteristics and behavior. The bald eagle is a sea or fish eagle.
   There are two subspecies of bald eagles. The "southern" bald eagle, Haliaeetus leucocephalus leucocephalus, is found in the Gulf States from Texas and Baja California across to South Carolina and Florida, south of 40 degrees north latitude. The "northern" bald eagle, Haliaeetus leucocephalus alascanus, is found north of 40 degrees north latitude across the entire continent. The largest numbers of northern bald eagles are in the Northwest, especially in Alaska. The "northern" bald eagle is slightly larger than the "southern" bald eagle. Studies have shown that "northern" bald eagles fly into the southern states and Mexico, and the "southern" bald eagles fly north into Canada. Because of these finding, the subspecies of "northern" and "southern" bald eagles has been discontinued in recent literature.

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 beak.
    Juvenile bald eagles are a mixture of brown and white; with a black beak in young birds. The adult plumage develops when they are sexually mature. It takes about five years for their head and tail feathers to gradually turn white.
    The bald eagle is the only eagle confined to North America. There are no other large blackish-brown birds with a white head and tail in North American.

Size - A female bald eagle's body length varies from 35 to 37 inches; with a wingspan of 79 to 90 inches. The smaller male bald eagle has a body length of 30 to 34 inches; with a wingspan ranging from 72 to 85 inches. An eagle's average weight is ten to fourteen pounds. Northern birds are significantly larger than their southern relatives.

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.
   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 scavenger 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.  


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.

Eyesight - 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.

 Skeleton - It weighs about half a pound (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.
bird skeleton

Habitat - Bald eagles live along the coast and on major lakes and rivers where they feed mainly on fish.

Longevity (life expectancy) - It's possible for bald eagles in the wild to live longer than thirty years, but the average lifespan is fifteen to twenty years. A captive eagle at West Stephentown, NY lived to be at least 48 years old.

Body Temperature - About 106 degrees Fahrenheit (41 degrees Celsius)

Eagles do not sweat, so they need to use other cooling methods such as perching in the shade, panting, and holding their wings away from their body.

Tolerance to cold temperatures - A bald eagle's skin is protected by feathers lined with down. Their feet are cold resistance, consisting of mostly tendon. The outside of the bill is mostly nonliving material, with little blood supply.

Golden eagles are larger than bald eagles in average height and wingspan, but there isn't much difference in average weight. One way to distinguish a golden eagle from an immature bald eagle is leg plumage. A golden eagle's legs are entirely feather covered; an immature bald eagle's lower legs are bare. As seen while in flight, juvenile golden eagles have white patches at the base of the primaries; the tail is white with a distinct dark terminal band. It takes four years to acquire adult plumage. Adult golden eagles are brown with tawny on the back of the head and neck; tail faintly banded.

Bald eagles are active during daylight hours (diurnal).

Fidelity - Once paired, bald eagles remain together for life. Although, if one dies, the survivor will not hesitate to accept a new mate.

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 up-drafts 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. Several eagles soaring in a thermal together is described as a "kettle of eagles."

   Bald eagles can fly to an altitude of 10,000 feet. During level flight, a bald eagle can achieve speeds of about 30 to 35 mph.

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 up-drafts. 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 interlocking of feathers is an astonishing design of nature. 
   Birds puff up their feathers for various reasons. They puff them up while preening; to insulate themselves to changing temperatures; when they're relaxed; to make themselves appear larger when threatened; and when they're ill.
   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.   Use of feathers permit.

Respiratory system - Eagles have an external naris on both sides of their beak. A bald eagle never reaches speeds that would interfere with normal breathing. An eagle's lungs and air sac system are 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. More about the respiratory system of birds

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.

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.

Above all other birds it is the soaring eagle, with its size and weight, that gives the most abiding impression of power and purpose in the air. It advances solidly like a great ship cleaving the swells and thrusting aside the smaller waves. It sails directly where lesser birds are rocked and tilted by the air currents.

   Bald eagles were officially declared an endangered species in 1967 in all areas of the United States south of the 40th parallel, under a law that preceded the Endangered Species Act of 1973.
   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 "threatened."
   On June 28, 2007 the Department of Interior took the American bald eagle off the Endangered Species List. The bald eagle will still be protected by the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act. The Bald Eagle Protection Act prohibits the take, transport, sale, barter, trade, import and export, and possession of eagles, making it illegal for anyone to collect eagles and eagle parts, nests, or eggs without a permit. Native Americans are able to possess these emblems which are traditional in their culture.