That Magnificent Black Eagle
By “Awake!” correspondent in South Africa
A HARSH cry is heard overhead. Two falcons are attacking a female black eagle in midair. Down hurtles one falcon, but the eagle meets the attack by rolling onto her back and extending her talons. Now both falcons dive, one behind the other. Again the eagle rolls to meet the first falcon. But can she sustain inverted flight long enough to deal with the second? With perfect control she executes a double roll just in time to ward off the second attack. What magnificent flying!
The black eagle, with a wingspan of 1.8 meters (6 ft.), is found from South Africa through East Africa and into Israel. As the name implies, the bird is glossy black in color. A white patch on the back forms a “V” over the shoulders. When the bird is in flight, pale patches at the wing tips give the wings a transparent appearance.
Well-made Nests
Usually the nesting site is an inaccessible ledge on a precipice. A pair of black eagles may have two, or even three sites—all in the same area—and may use them, in turn, according to fancy. Rotating the use of the nests may assist in keeping them free from parasites. Black eagles are scrupulously clean.
The nest is well made and is enlarged and remodeled each time it is used. It may be 1.5 meters (5 ft.) across at the base and almost as high and is made of sticks as thick as the human thumb. Both the male and the female birds contribute to the building of the nest. However, while the male may place the sticks where he feels they are best suited, his mate will often rearrange them. In doing this, she may eventually return a stick to its original position; but she is then satisfied that this is the best place. The nest is no haphazard pile of sticks.
The depression in the center of the nest is finally lined with green twigs and leaves that are renewed frequently. This serves as a soft lining and may also provide the humidity needed for hatching the eggs.
An Elaborate Courtship
In the middle of May, after nest repairs have been made, an elaborate courtship commences. This is not for the purpose of winning a mate, as these eagles mate for life, and some may live for 50 years. Rather, it is a preliminary to mating, and both eagles share in thrilling flight displays.
At times the male will descend on the flying female, and she will roll over at his approach. The pair lock talons and fall, spinning for a considerable distance before they separate. At other times, the birds will climb and dive on a course like that of a swinging pendulum, turning at the end of the swing by wheeling over on one wing. The ratios of weight times wing area and wing length times breadth provide an excellent compromise for an eagle’s flight requirements.
Rearing a Chick
Eggs are laid by black eagles in the early part of June. Usually there are two eggs, with an interval of one to four days between them, and they are incubated for about 44 days. The male shares with his mate in sitting on the eggs during daylight, but the female always takes the full night watch.
Although two eggs are in the nest, only one eaglet will be raised. Sometimes the female will destroy one of the eggs when it is evident that a live chick is in the other. On other occasions, both will be allowed to hatch. When that is the case, the firstborn chick usually dominates the other one, which soon dies. The parents do nothing to prevent this, although there is ample food for both birds. Why?
The reason for instinctive limiting of the family is not clear. It definitely is not due to a shortage of food. The thorough training that an eagle requires may be a factor, since one chick seems to occupy the full attention of both parents.
But why, then, should there be two eggs? If only one egg were laid, there would be times when, through infertility, accident or the action of predators, it would be lost. Two eggs increase the chances of a successful hatching and ensure the survival of the eagle. When two hatch, if something should be wrong with the firstborn, the second-born chick would be dominant and survive its older sibling.
The tapping by the chick on the egg shell is the signal to the male bird that a hatching is imminent. He hunts for a tender young rock hyrax (Procavia capensis, the “rock badger” of the Bible [Lev. 11:5]). Under normal circumstances, this creature makes up 99 percent of the black eagle’s diet. The hyrax weighs up to 4.1 kilograms (9 lbs.) and is usually eaten entirely—flesh, skin and bones. That may seem strange, but the bones provide calcium, essential to the eagle’s diet. The skin, with its fur, seems to serve as an aid to digestion.
The choicest portions of the prey are fed to the hatched chick, which resembles a small ball of white down. It eagerly takes the strips of meat torn from the carcass by the parent. As the chick grows older, it learns how to strip a carcass and to swallow such awkward parts as the bones and skin.
There are other things that the chick must be taught early in life. For the nest to remain clean, the chick must learn to defecate over the rim of the nest, paying attention to the direction of the wind. The mother may move the chick by putting a foot under it and walking the little one to the rim of the nest until it learns to relieve itself in the right place. As the bird gets older, a firm foot placed on its foot and a meaningful stare suffice to convey the thought that it must move.
The rearing of an eagle manifestly takes much time. In fact, 95 to 100 days will pass before the young eagle will fly.
The Eaglet Flies
As the time for the first flight approaches, the eaglet becomes increasingly frustrated by the restrictions of the nest. It watches other birds, stretches its wings and legs, flaps its wings and jumps up and down. The feathers are fully grown, but the plumage is not the glossy black of the parents. The young bird is a mottled brown and russet color and will not attain adult plumage until the third-year molt. The parents sense that the time for flight is near and stop bringing food to the nest for a day or so. No doubt it is best for the first flight to be undertaken on an empty stomach!
What starts the youngster on the maiden flight? It is usually a call from the parents, made from a nearby perch or as they fly by. If all else fails, an unexpected push will propel the eaglet into space. With the sensitive primary feathers at the wing tips, the eaglet feels the pressure and movement of the air. At this stage, however, the bird does not know how to act on the information received, and so the flight is short-lived. Down the mountainside the youngster goes, to the lower slopes, there to make an ungainly landing and to rest, with rapidly beating heart. At that, the parents feed their offspring. Then, with confidence restored, the young bird is ready to try again. A few more awkward attempts and it will begin to master wing control.
A Thorough Education
The art of hunting comes next in the program of education. Often both parents put on an aerial display, attracting the attention of the hyraxes, which enjoy sitting on sunbaked rocks, keeping a wary eye on their enemy—the black eagle. Eventually, one eagle will drop low and, using the cliffs for cover, will make a rapid sweep around a corner and pick up an unsuspecting hyrax from behind. Death comes instantly. With the force of the swiftly flying bird behind it, the rear talon penetrates the prey. The fore talons close in a lock, and the dead hyrax is swung forward, to be carried in one claw to the “butcher block,” often a rock, where the prey will be decapitated and dismembered. The young eagle observes these actions.
Much work goes into making the young eagle a proficient flier. The bird must learn how to ride the winds deflected upward by a precipice, how to swoop and how to soar. For long trips, an eagle chooses a day when the wind is blowing in the direction opposite of flight. Then, when the sun is up and warming the air in the valleys, the bird launches itself from a rock perch. Soon a bubble of heated air is found. By turning within it, the eagle rises to perhaps 4,000 meters (13,000 ft.). With the lift of the air petering out, the bird turns toward its destination. By planing down, the eagle maintains momentum. At the same time, the flow of the wind over the wings imparts lift. In this way hundreds of miles may be covered with no more than a few flaps of the wings at the time of taking off.
Fully equipped for its role in life, the young eagle is escorted from home by the parents. Taking their offspring far afield, they leave it to find a mate and to establish a home of its own.
At the sight of an eagle in the skies, we may well exclaim, ‘How magnificent!’ The study of earth’s creatures can indeed be absorbing. We marvel at the beauty of design evident in the animal creation. Not only do such creatures fill a necessary niche in the whole balance of the natural world; they do so with a grace and beauty that reflect the qualities of their Creator. We must agree with the Bible writer Agur, who marveled at “the way of an eagle in the heavens.”—Prov. 30:18, 19.