CONSUMPTION OF FOOD— FLYING CAPACITY-WALKING, ETC. 



From these bones of the bird's hand (it, o) arise the great quill 

 feathers or primaries of the wings, usually ten in number. These, 

 by their form, stiffness, and relative strength, indicate the power 

 of flight. The secondaries spring from the principal bone of the 

 forearm (7),.and are generally stouter, longer, and more flexible 

 than the primaries, differing considerably less from the general 

 covering of the body. Their number varies in the different kinds 

 of birds. From the bone of the upper arm (humerus) springs an- 

 other class of feathers, called the tertiaries* These, in many birds, 

 as in the Plover, Curlew, and others, are greatly lengthened ; but 

 are weaker in their structure than the secondaries. Two, or, gen- 

 erally, three short and stiff feathers form the thumb (Plate B), and 

 are called the bastard wing, winglet, or spurious wing. These lie 

 upon the base of the first primaries, at the edge of the wing. Be- 

 sides these, and corresponding with the series of feathers, there 

 are, both on the outer and inner surface of the wing, several rows 

 of smaller feathers, called coverts, from their protecting the basal 

 part of the quills. 



The covering feathers of the body do not cover it equally all over, 

 but form single rows or patches, so that, in fact, the larger part of 

 a bird's body is not covered at all. These rows of covering feath- 

 ers vary in the different kinds of birds. The birds that have an 

 even covering of feathers all over are unable to fly. The feathers 

 of the body lay over each other like shingles on a roof — the large 

 feathers of the wings and of the tail resembling a fan. 



Great Consumption of Food. 



No other animals undergo such rapid transformations of the bod- 

 ily tissues ; none have such warm blood as birds. It is the in- 

 creased capacity for breathing that gives to birds such an increase 

 of activity and power. They inhale larger quantities of air than 

 other animals. Not only the lungs, but also the air bladders, the 

 hollow bones, the cells of the bones, and also, sometimes, peculiar 

 cells of the skin, are filled with air. The blood contains more 

 oxygen than the blood of other animals, and its circulation is more 

 rapid and powerful. The arteries in birds are comparatively 

 thicker ; the blood is redder, and contains more globules, than that 

 of other vertebrates. Hence arise the unsurpassed mobility of birds 

 and their wonderful power of digestion. 



Birds eat more in proportion to their size than any other animals 

 belonging to the class of vertebrates. Not a few of them eat as 

 long as they are awake, and many of those that live on insects, con- 

 sume daily two or three times their own weight. But flesh-eaters 

 consume daily only about one-sixth of their weight, and plant-eat- 

 ers about the same ; yet we shall be compelled to call these birds 

 gluttinous, if we compare them in this regard with mammals. Many 

 birds fill the throat with food up to the bill, and others so fill the 

 crop that it stands out like a ball on the neck. Birds of prey even 

 digest old bones ; while the larger grain-eaters so work pieces of 

 iron or needles in their gizzards, that the forms of these articles are 

 considerably changed, or their sharp points altogether disappear. 

 Indigestible food often lies for weeks in the stomachs of birds. 

 Bones, hair, etc., are often found in the stomachs of birds of prey, 

 wrought into balls, which the birds disgorge at their will. In spite 

 of the rapid changes of tissue in birds, large quantities of fat col- 

 lect under the skin and between the intestines. But a few days of 

 hunger will dissipate this surplus. Yet birds endure hunger, or 

 want of food, longer than some mammals. The mole, for example, 

 will, if destitute of food, die in a few hours. 



The Flying Capacity of Birds. 



Compared with those of other animals, all the voluntary motions 

 of birds are quicker and more enduring ; their muscles are more 

 compact, stronger, and more irritable, contracting more power- 

 fully. All other animals, capable of flying or moving through the 



air, flutter merely. Birds fly. This is due to the construction of 

 their wings. All the wing feathers lie like shingles lapping over 

 each other, and so curved as to give the wing a convex appear- 

 ance upward. When the wings are raised, the connection of the 

 single feathers is loosened, and the air rushes between them ; on 

 the other hand, when the wings are pressed down, all the feathers 

 become closely locked to each other, and offer considerable resist- 

 ance to the air. The bird necessarily rises by each stroke of its 

 wing, and when the stroke is made from the front backward, and 

 from above downward, a forward movement is gained. The tail 

 serves as a rudder, and is a little raised in ascending, and pressed 

 down in descending, and in turning round, either to the right or 

 left. The strokes of the wings, in perfectly accomplished flyers, 

 are at times quicker or slower, or cease altogether ; the wings being 

 more or less turned, with the front border sometimes higher and 

 sometimes lower than the hinder part, according as the bird intends 

 to fly more quickly upward or forward, or sail ahead, or reverse 

 its course. If the bird intends to dart downward from a great height 

 in the manner of Hawks, the wings are completely drawn in ; the 

 evolved form of the wing requires a counter-wind, for the current 

 of air in front fills the wing and raises the bird, while the rear 

 wind, or current of air, loosens the feathers, and presses the bird 

 downward. 



The relative velocity and manner of flight depend upon the shape 

 of the wing and the construction of the feathers. Long, slender, 

 sharp-pointed, and stiff-feathered wings contribute to a rapid flight ; 

 short, broad, and rounded wings and loose feathers allow only a 

 slow flight. A proportionally long and broad tail makes sudden 

 turns possible. Large, rounded, and broad wings facilitate longer 

 continued hovering. The flying velocity of some birds is remark- 

 able. For example, the Swallow and Eagle dart through the air 

 at the rate of about seventy-five miles an hour ; the Falcon, at the 

 rate of sixty miles an hour, and the wandering Pigeon literally out- 

 strips the wind. Other birds, in a few days, fly across wide seas. 

 Birds of passage fly for days without any cessation ; hovering 

 birds play for hours in the air, and only the most untoward condi- 

 tions can cause them finally to desist. It is wonderful how a bird, 

 at the most different and the greatest heights, flies with the same 

 comparative ease. Humboldt, when almost at the highest point 

 of Chimborazo, observed a Condor flying at such an immeasurable 

 height above him as to present the appearance of a small dot, and 

 yet apparently flying with the same ease as in a much denser at- 

 mosphere. But this must have been only apparently, since Pig- 

 eons, let loose by aeronauts at great heights, fly very insecurely, 

 until they reach lower and denser regions of the atmosphere. 



Walking and Swimming. 



Walking. — The perfect flyers among birds are, as a rule, inca- 

 pable of walking. An excepted few only can walk with ease. 

 The walk of birds is various. There are runners, trotters, cursors, 

 jumpers, steppers, walkers, and, finally, some unskilled sliders and 

 waddlers. All birds, except a few swimmers, walk on their toes. 

 Those that have the center of gravity corresponding with the cen- 

 ter of the body, walk the best, if not the quickest. High-legged 

 birds walk well, but with measured steps; the short-legged walk 

 badly, usually hopping, and those with middling long legs walk 

 rather quickly, their movement being more like a run than a walk. 

 Birds having a more erect posture, and those with their legs far be- 

 hind, move heavily and awkwardly. Some good flyers can not 

 walk at all, and some excellent divers only slide or waddle. Many 

 birds use their wings to assist them in walking. 



Swimming and Diving. — Not a few birds move with ease in the 

 water, and every bird swims, if thrown upon the water. The 

 swimmers proper, like all birds living on the water, have a denser 

 plumage than the land birds. Their plumage is always richly 



