which is Latin for rudders. But the short ones are called coverts, like those of the wings—upper tail-coverts, and under tail-coverts."
"How funny!" said Dodo, "for a bird to have to row himself and steer himself all at once. I know I should get mixed up if I tried it with a boat. How do feathers grow, Uncle Roy?"
"Just like your hair, little girl," said the Doctor, patting her on the head, "or your nails. Didn't you ever notice the dots all over the skin of a chicken? Each dot is a little hole in the skin where a feather sprouts. It grows in a sheath that pushes out of the hole, like a plant coming up out of the ground from its root. For a while this sheath is full of blood to nourish the growing feather; that is why new feathers look dark and feel soft—pin-feathers they are called. The blood dries up when the feather has unfolded to its full size, leaving it light and dry, with a horny part at the root that sticks in the hole where it grew, and a spray-like part that makes up most of the feather. The horny part becomes hollow or contains only a little dry pith; when it is large enough, as in the case of a rowing feather from a Goose's wing, it makes a quill pen to write with. But the very tiniest feather on this Sparrow is built up in the same way.
"See! here is one," continued the Doctor, as he twitched out a feather from the Sparrow's back. "You see the quill part runs in the middle from one end to the other; this is called the shaft. On each side of it all along, except just at the root, the spray-like parts grow. They are called the webs or vanes. Now look through this magnifying glass at the web."
The children looked in turn, and each, exclaimed in wonder at the sight.
"Yes, it is very wonderful. The web, that looks so smooth to the naked eye, is made up of a great many small shafts, called barbs, that grow out of the main shaft in rows. Every one of these small side-shafts has its own rows of still smaller shafts; and these again have little fringes along their edges, quite curly or like tiny hooks, that catch hold of the next row and hold fast. So the whole feather keeps its shape, though it seems so frail and delicate."
"Are all feathers like this one?" asked Rap.
"All are equally wonderful, and equally beautiful in construction; but there is a good deal of difference in the way the webs hold together. Almost all feathers that come to the surface are smooth and firm, and there is not much difference except in size, or shape, or color. For example, the largest wing-feather or tail-feather of this Sparrow is quite like the one I pulled out of its back in texture, only the back-feather is smaller and not so stiff. But near the roots of these feathers you notice a fluffy part, where the webs do not hold together firmly. Some feathers are as fluffy as that in their whole length. Such are called down-feathers, because they are so downy. Birds that run about as soon as they are hatched are always clothed in down, like little chickens, before their other feathers sprout; and some birds, like Ducks, wear a warm underclothing of down their whole lives. Then again some feathers do not have any webs at all—only a slender shaft, as fine as a hair."
"Do feathers keep on growing all the time, like my hair?" asked Dodo.
"No, my dear. They stop growing as soon as they are of the right size; and you will find your hair will do the same, when it is long enough—though that won't be for a good many years yet, little girl. When the blood that has fed the growing feather is all dried up, the feather ceases to grow. Then after a while longer, when it has become ragged and worn, it gets loose in the skin and drops out—as I am sorry to say some of my hair is doing already. That is what we call moulting."
"I know about that," interrupted Nat. "It's when hens shed their feathers. But I didn't know that it was moulting when people grow bald."
"It is very much the same thing," said the Doctor, "only we don't call it moulting when people lose their hair. But there is this difference. Birds wear out their feathers much faster than we do our hair, and need a new suit at least once a year, sometimes oftener. All young birds get their first new clothes when the down is worn out. Old birds generally moult as soon as they have reared their broods, which in this country is late in summer or early in the fall. Many also moult again the following spring, when they put on their wedding dress; and one of the curious things about this change of plumage is, that the new feathers often come out quite unlike those that were cast off. So a bird may differ much in appearance at different seasons and ages—in fact, most birds do. The male also differs in many cases from the female, being more handsomely dressed than his mate."
"I don't think that's fair," said Dodo. "I shouldn't like Nat to have nicer clothes than I wear."
"But it is best for Bird People," replied the Doctor, "that the mother bird, who has to keep house and tend to the little ones, should not be too conspicuous. She is best protected from enemies when her colors are plain, and especially when they match the foliage in which she sits on her nest. If her mate has only himself to look out for, it does not so much matter how bright his plumage may be. The colors of some birds are so exactly like their surroundings, that you might look long before you could find the sober, quiet female, whose mate is flashing his gay plumage and singing his finest song, perhaps for the very purpose of attracting your attention away from his home. 'Protective coloration,' is what the Wise Men call it."
"What makes all the different colors of birds, Doctor?" asked Rap.
"That is a hard question to answer. It is natural for birds to have particular colors, just as some people have black eyes and hair, while others have blue eyes and yellow hair. But I can tell you one thing about that. Look at this Sparrow. All the colors it shows are in the feathers, whose various markings are due to certain substances called 'pigments,' which filter into the feathers, and there set in various patterns. The feathers are painted inside by Nature, and the colors show through. You see none of these colors are shiny like polished metal. But I could show you some birds whose plumage glitters with all the hues of the rainbow. That glittering is called 'iridescence.' It does not depend upon any pigment in the substance of the feathers, but upon the way the light strikes them. It is the same with the beautiful tints we see on a soap-bubble. The film of water itself is colorless, but it becomes iridescent. You might divide all the colors of birds into two classes—those that depend upon pigments in the feathers, and those that depend upon the play of light on the feathers."
"That's pretty hard to remember," said Nat; "but I know how a soap-bubble looks, though I never saw any birds look that way. Please show us one."
"I will show you two," answered the Doctor, who then went to his glass case, and took out a Wild Pigeon and a Hummingbird. "Look at the shining tints on the neck of this Pigeon, and see how the throat of this Hummingbird glitters when I turn it to the light."
"That's the prettiest color I ever saw," said Nat, "and I can remember about it now. But," he added, thinking of the way he had seen hens mope when they were moulting, "does it hurt birds to lose their feathers, uncle?"
"It is probably not as comfortable as being nicely dressed, and sometimes they seem quite miserable, especially if they shed old feathers faster than new ones can grow to replace the lost ones. Some birds, like Ducks, lose their wing-feathers all at once, and cannot fly for quite a while. But Heart of Nature is kind to his children, as a rule. Most birds shed their rowing feathers one at a time in each wing, so that they never lose their power of flight. Now this will do for wings, tails, and feathers. Come! what is the next thing you notice about this Sparrow? Is it entirely covered with feathers?"
"Of course it isn't," said Dodo; "it hasn't any feathers on its beak or on its feet, else how could it eat and hop about?"
"That is right. These parts of a Sparrow are bare; they never have any feathers; and the skin on them is hard and horny, as different from soft thin skin as finger-nails. Now look at the beak, and think how many things a Sparrow has to do with
