Bald Eagle

My favorite bird is the Bald Eagle, so I decided to research the status of this majestic bird for today's blog posting.

On June 28, 2007 the Department of Interior took the American bald eagle off the Federal list of endangered and threatened wildlife and plants. The bald eagle will still be protected by the Migratory Bird Treaty Acct and the Bald and Golden Eagle Protection Act.   

The number of nesting pairs in the lower 48 United States increased 10-fold, from less than 450 in the early 1960s, to more than 4,500 adult bald eagle nesting pairs in the 1990s. In the Southeast, for example, there were about 980 breeding pairs in 1993, up from about 400 in 1981. The largest concentrations were in the states of Florida and Louisiana. Today, there are an estimated 9,789 nesting pairs of bald eagles.

Bald Eagles, like many birds of prey, were especially affected by DDT. This insecticide chemical itself was not lethal to the adult bird, but it interfered with the bird's calcium metabolism, making the bird either sterile or unable to lay healthy eggs. Female eagles laid eggs that were too brittle to withstand the weight of a brooding adult, making it nearly impossible for the eggs to hatch. It is estimated that in the early 18th century, the Bald Eagle population was 300,000–500,000, but by the 1950s there were only 412 nesting pairs in the lower 48 states of the US. Other factors in Bald Eagle population reductions were a widespread loss of suitable habitat, as well as both legal and illegal shooting. In 1930 a New York City ornithologist wrote that in the state of Alaska in the last 12 years approximately 70,000 Bald Eagles had been shot. Many of the hunters killed the Bald Eagles under the long held mistaken beliefs that Bald Eagles grabbed young lambs and even children with their talons.

The bald eagle (Haliaeetus leucocephalus), our 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 "northern" bald eagle is slightly larger than the "southern" bald eagle.

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. Bald eagles are active during daylight hours. 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.

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.

Lifting Power - A bald eagle can lift up to four 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).

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.

Fidelity - The eagle is sexually mature at four years or five years of age. 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.

Feathers - 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.

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.