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Bald Eagles are fascinating birds. In addition to being large, graceful, and "tough," they are rare among the animal kingdom in that they
- mate for life
- remain pretty much in the vicinity of their hatching
- take turns (male/female) nesting - warming and protecting eggs
- store up food in "nature's refrigerator" to insure ample food upon hatching (Eagle parents lose almost a quarter of their body weight while awaiting hatching and storing food)
In 1963 the bald eagle population in the continental United States was reduced to just 417 known breeding pairs. Today, there are more than 7,678 pairs of bald eagles in the contiguous United States. As a result, although still protected, they have been removed from the "threatened" list.
The eyesight of eagles is legendary. 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.
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 iit may be overcome by hypothermia.
The eggs hatch in the order they were laid. Eaglets break through the shell by using their egg tooth, a pointed bump on the top of the beak. It can take from twelve to forty-eight hours to hatch after making the first break in the shell (pipping). Once the eggs begin to hatch, the female's vigilance becomes nearly constant. The male provides the majority of the food needed by his rapidly growing family. Eventually the female will take up her share of the hunting, but in the early days, all of her attention is given to the young eaglets in the nest.
Chicks - Sometimes two chicks will survive, but it is not uncommon for the older eaglet to kill the smaller one, especially if the older is a female, as females are consistently larger than males. Should one chick decide to kill its sibling, neither parent will make the slightest effort to stop the fratricide.
Newly hatched, eaglets are soft, grayish-white down covers their small bodies, their wobbly legs are too weak to hold their weight, and their eyes are partially closed eyes, limiting vision. Their only protection is their parents.
Eagles feed their young by shredding pieces of meat from their prey with their beaks. The female gently coaxes her tiny chick to take a morsel of meat from her beak. She will offer food again and again, eating rejected morsels herself, and then tearing off another piece for the eaglet.
While on the nest with very young eaglets, parents move about with their talons balled into fists to avoid accidentally skewering their offspring.
Eaglet Growth - The young birds grow rapidly, they add one pound to their body weight every four or five days. At about two weeks, it is possible for them to hold their head up for feeding. By three weeks they are 1 foot high and their feet and beaks are very nearly adult size. Between four and five weeks, the birds are able to stand, at which time they can began tearing up their own food. At six weeks, the eaglets are very nearly as large as their parents. At eight weeks, the appetites of the young birds are at their greatest. While parents hunt almost continuous to feed them, back at the nest the eaglets are beginning to stretch their wings in response to gusts of wind and may even be lifted off their feet for short periods.
At three or four weeks, this eaglet is covered in its secondary coat of gray down. In another two weeks or so, black juvenile feathers will begin to grow in. While downy feathers are excellent insulators, they are useless as air foils, and must be replaced with juvenile feathers before an eaglet can take its first flight, some 10 to 13 weeks after hatching. Unfortunately, approximately 40% of young eagles do not survive their first flight.The young eagle stays near the nest, practicing its abilities to fly and to hunt. The parents cannot tell juveniles how to hunt, they have to learn by watching the parents and by practicing. During this time they seem to spend more time looking at prey than they do actually attacking it.
Over the next month, they meet with their parents to be fed, but have little other contact with them. They learn to soar and to spot prey. Until the first winter after their fledging, young eagles near the nest are often still fed by their parents. Although a young eagle has the instincts to hunt, it lacks the skills. If food is scarce during the winter, it may die.
Six to nine weeks after fledging, juvenile eagles leave the nesting.
Nesting cycle - From the time the parents build the nest and the young are on their own, takes about 20 weeks. During the nesting cycle the parents remain within one to two miles of the nest. 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.
Size - The female bald eagle is 35 to 37 inches, slightly larger than the male. With a wingspan which varies from 79 to 90 inches.The male bald eagle has a body length from 30 to 34 inches. The wingspan ranges from 72 to 85 inches.Bald eagles weigh from ten to fourteen pounds. Alaskan eagles are significantly larger than their southern relatives.
Longevity - Wild bald eagles may live as long as thirty years, but the average lifespan is probably about fifteen to twenty years.
Body Temperature - 102 degrees Fahrenheit (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.
Fidelity - Once paired, bald eagles remain together until one dies. Once "widowed" 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.
Near Juneau, eagles are extremely plentiful and visible. They feed predominantly on the plentiful fish (salmon and herring) that venture too near the surface. They can soar such that they almost appear still, or fly and dive at speeds over 40 miles an hour!
