Chapter 10

THE BUILDING OF A BIRD

It rained on Wednesday--a warm spring rain, swelling the rivers and ponds, and watering the newly planted garden; but discouraging the birds in their nest-building, and disappointing Nat and Dodo, who wished to have their lesson in the orchard.

"Come in here, children," said the Doctor. "The wonder room, as Dodo calls it, is a good place for a talk about feathers and bones, and the rest of the things birds are built of. I have sent for Rap, too, so that the trio may be complete."

"Feathers and bones for building birds?" said Nat. "What a queer idea for a bird story."

"Not a bird story exactly," answered the Doctor. "But some things are true of all birds, and you must know them if you wish to understand the _reason why_ of any bird in particular."

In a few minutes the three children were seated on the wide settle, with a cheery log fire, to make them forget the outside dampness. Quick, the fidgety little fox-terrier, sat by the hearth, watching a possible mouse hole; and Mr. Wolf, the tawny St. Bernard, chose the rug as a comfortable place for finishing his morning toilet.

Olive presently joined the group. The Doctor took the dead White-throated Sparrow from the table, and began to walk about the room, stopping now in front of the fire and then by the window.

"Here is a Sparrow, different from every other kind of Sparrow, different indeed from any other sort of bird in the world--else it would not be the particular sort of a Sparrow called the White-throated. But there are a good many things that it has in common with all other birds. Can you tell me some of them?"

"I know!" said Dodo; "it has a good many feathers on it, and I guess all kinds of birds wear feathers, except some when they are very little in the nest."

"Quite right, little girl," said the Doctor. "Every bird has feathers, and no other animal has feathers. So we say, 'A bird is known by its feathers.' But what do you suppose its feathers are for?"

"To make it look nice and pretty," said Dodo promptly.

"To make it lighter, so's it can fly," added Nat.

"To keep it warm, too, I guess," was Rap's answer.

"Well, you are all three partly, but not quite, right. Certainly the beauty of a bird depends most on its feathers, being not even skin-deep, as you may well believe, if you ever noticed a chicken Mammy Bun had plucked. But, Nat, how can feathers make a bird lighter, when every one of them weighs something, and a bird has to carry them all? They make a bird a little heavier than it would be without them. Yet it is quite true that no bird could fly if you clipped its wings. So some of its feathers enable it to fly--the large ones, that grow on the wings. Then, too, the large ones that make the tail help the bird to fly, by acting like a rudder to steer with. Perhaps the small ones too, all over the body, are of some help in flight, because they make a bird smooth, so that it can cut through the air more easily--you know they all lie one way, pointing backward from their roots to their tips. Then when Rap said feathers keep a bird warm, he guessed right. Birds wear plumage as you do clothes, and for the same purpose--to look nice and keep warm."

"But what is 'plumage,' Uncle Roy?" asked Dodo; "I thought you were talking about feathers."

"So I was, missy. Feathers are the plumage, when you take them all together. But see here," added the Doctor, as he spread the Sparrow's wings out, and held them where the children could look closely; "are the wings all plumage, or is there something else?"

"Of course there's something else to wings," said Dodo; "meat and bones, because I've eaten chickens' wings."

"Why didn't you say, Dodo, because there has to be something for the feathers to stick into?" said Nat decidedly.

"You both have very good reasons," said the Doctor. "The plumage of the wings grows out from the skin, just as feathers grow from any other part of the body, only the large ones are fastened to the bones, so that they stay tight in their proper places. If they were loose, they would fly up when the bird beats the air with its wings, and get out of order. See how smoothly they lie one over another! When the bird closes its wings, they come together snugly along its sides. But when the wing is spread, they slide apart--yet not too far to form a broad, flat surface, quite stiff, but light and elastic. By beating the air with the wings birds fly along. It is something like rowing a boat. This surface pushes against the air as the flat blade of an oar pushes against the water. That is why these large stiff feathers are called the rowers. When the Wise Men talk Latin among themselves, they say _remiges_, for 'remiges' means rowers."

"But, Doctor," said Rap, who was looking sharply at the Sparrow's wing, "all the feathers are not like that. Here are a lot of little ones, in rows on top of the wing in front, and more like them underneath, covering over the roots of the rowing feathers. Have they any name?"

"Oh, yes! Everything you can see about a bird has its own name. Those small feathers are called _coverts_, because they cover over the roots of the rowers. Those on top are the upper coverts; those underneath are the under coverts, or lining of the wings. Now notice those two pretty bands of color across the Sparrow's wing. You see one band is formed by the tips of the longest coverts, and the other band by the tips of the next longest coverts. Those two rows of feathers are the greater and middle coverts, and all the smallest feathers, next to the front edge of the wing, are called lesser coverts. Now look at the tail, Rap, and tell me what you can find."

"Why, there is a bunch of long stiff feathers like rowers, that slide over each other when you spread the tail, and a lot of short feathers that hide the roots of the long ones. Are they rowers and coverts too?" "A bird does not row with his tail--he steers with it, as if it were a rudder; and the long feathers are therefore called rudder-feathers--or _rectrices_, 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 it. He has no hands or paws, and so he must pick up everything he eats with his beak. He has no teeth, and so he must bite his food with his beak. He feeds on seeds like a Canary bird; so his beak comes to a sharp point, because seeds are small things to pick up; and it is very strong and horny, because seeds are hard to crack, to get at the kernel. Notice, too, children, that his beak is in two halves, an upper half and a lower half; when these halves are held apart his mouth is open, so that you can see the tongue inside; and when the two halves are closed together the mouth is shut. These halves are called the _upper mandible_ and the _lower mandible_."

"Why, it's just like people's mouths," said Nat, "only people have lips and teeth."

"Certainly it is like our mouths. Birds are built like ourselves in a great many things, and live as we do in a great many ways. Bird People and House People are animals, and all animals must eat to live. A bird's beak is its mouth, and the under mandible moves up and down, like our chins when we eat or talk. Birds can talk as well as sing with their beaks. This Sparrow can say 'Peabody,' and some kinds of Parrots can repeat whole sentences so as to be understood. That is another thing in which birds' beaks are like our mouths. Now look again--can you see anything else about the Sparrow's beak?"

"I see a pair of little holes at the root of the upper mandible," said Rap.

"Well, those are the nostrils!" said the Doctor. "Birds must breathe, like ourselves, and when the beak is shut they breathe through the nostrils."

"So do I," said Dodo; and then she pursed up her pretty red lips tightly, breathing quite hard through her nose. "I do think," she said, when she had finished this performance, "birds have faces, with all the things in them that we have--there are the eyes, too, on each side, like people's eyes, only they look sideways and not in front. But I don't see their ears. Have birds any ears, Uncle Roy?"

"I can show you this Sparrow's ears. See here," said the Doctor, who had run the point of his penknife under a little package of feathers on one side of the back of the Sparrow's head, and lifted them up; "what does that look like?"

"It's a hole in the skin that runs into the head," said Nat. "Can birds hear through that?"

"Of course they can. Ears of all animals are made to hear with. This Sparrow can hear quite as well as you can, Nat. Now think, children, how many things we have found about this Sparrow's head that are quite like our own,--ears, eyes, nose, mouth, and tongue,--only there are no lips or teeth, because the horny beak, with its hard edges and sharp point, answers both for lips and teeth. I want you to learn from this how many things are really alike in Bird People and House People, though they look so different at first sight. When we come to the bird stories, you will find that birds differ very much among themselves in all these things. I will show you all sorts of beaks, of different sizes and shapes. Here are pictures of several kinds of beaks--see how much they differ in shape! But they are all beaks, and all beaks are mouths. They all answer the same purposes in birds' lives, and the purposes are the same as those of our mouths. But now, what do you notice about this Sparrow's feet?"

"They are not a bit like my feet," said Dodo; "they are so long and slim and hard, and the toes stick out so all around. I think mine are nicer."

"But they would not be so useful as this Sparrow's if you had to live in a bush and hop about on the twigs," said the Doctor. "The bird's feet are fixed as nicely for that, as yours are for walking on the ground. I can show you, too, little girl, that a Sparrow's feet are a great deal more like yours than you think. Come, Rap! Tell me what you see about this bird's feet."

"Why, they are the ends of its legs, and there is a long slim part beyond the feathers, hard and horny like the beak, and at the end of this are four toes, three in front and one behind, and they've all sharp claws on their ends."

"Very well said, my boy! Now I will show you that such feet as the Sparrow has are as much like Dodo's as a Sparrow's beak is like her mouth. Begin with the claws--"

"I know!" exclaimed Dodo, "toe-nails! Only I think they need cutting!"

"Of course they are toe-nails," said the Doctor. "Don't nails grow on the ends of toes? All kinds of claws, on the ends of birds' and other animals' toes, are the same as nails. Some are long, sharp, and curved, like a cat's or a Sparrow's, and some are flat and blunt, like ours. I could show you some birds with claws that look just like our finger-nails. Toes, too, are pretty much the same; only this Sparrow, like most other birds, has but four, with three of them in a line in front, and the other one pointing backward. That is what makes its foot as good as a hand to hold on with when it perches on slender twigs. Almost all birds have their toes fixed that way. Some, that do not perch, have no hind toe; and birds that swim have broad webs stretched between their front toes, like Ducks. All the different kinds of feet birds have are fitted for the ways they move about on the ground, or water, or among the branches of trees and bushes, just as all their shapes of beaks are fitted for the kind of food they eat and the way they pick it up. Here are two pictures that will show you several different kinds of feet. Now you must answer the next question, Nat; what do toes grow on?"

"Feet!" said Nat promptly, then adding: "But this Sparrow hasn't any feet except its toes; they grow on its legs, because the rest of the horny part stands up--I've noticed that in Canaries."

"But all this horny part is the foot, not the leg," answered the Doctor, "though it does stand up, as you say. How could toes grow from legs without any feet between? They never do! There has to be a foot in every animal between the toes and the legs. Now what do you call the end of your foot which is opposite the end on which the toes grow?"

"It's the heel in people, but I should think the hind toe of a bird was its heel," said Nat doubtfully, and beginning to think he did not understand.

"You might think so," said the Doctor; "but you would be wrong. All this horny part that a bird stands up on is its foot. And the top of it, nearest to the feathers, is the heel. Don't you see, when I bend the foot _so_," continued the Doctor, as he bent the Sparrow's foot forward, "that the top of the horny part makes a joint that stands out backward, in the same position your heel always has? All this slender horny part of the foot, above the roots of the toes, corresponds to the instep of your foot, and of course the heel comes next. You must remember the name of it--the Wise Men call it the _tarsus_."

"Then hasn't a bird got any legs, Uncle Roy, only just feet?" asked Dodo.

"Oh! yes; legs too, with a knee-joint and a hip-joint, like ours. But all these parts are up closer to the body, and hidden by the feathers, so that you cannot see them."

As the Doctor said this there was a great commotion. Quick, who had been watching the mouse hole all the while, gave a sharp bark and pounced on something. There was a feeble squeak, and it was all over with a mouse which had ventured too far from its hole.

"Poor little mousey!" said the Doctor, as he took the limp body from the terrier's mouth. "It is quite dead. I am sorry, but it might have nibbled some of my birds. Besides, this is exactly what I wanted to teach you something about. Who can tell me the difference between a mouse and a Sparrow?"

"I can!" said Dodo; "it's all difference; a mouse hasn't any feathers, or any wings, and it has four feet, and a long tail and whiskers and teeth--"

"That will do, little girl, for differences; do you see anything alike between a Sparrow and a mouse, Rap?"

"I think the fur is something like feathers, Doctor," answered Rap; "and you told us how a beak was like a mouth without any teeth or lips; then a mouse has four feet and legs; but a bird has only two feet, and two wings instead of four legs and feet like a mouse."

"That is just what I want you all to think about," said the Doctor. "Now listen. If a Sparrow has a pair of feet that correspond to a mouse's hind feet, what do you think a Sparrow's wings correspond to in a mouse?"

"I should think they would be something like a mouse's fore feet," answered Rap, after thinking a moment.

"That is exactly right. Birds and beasts are alike in many respects. They have heads, necks, and bodies; they have tails; and they have limbs. Beasts have two pairs of limbs. We call them fore legs and hind legs. People have two pairs also. We call them arms and legs. So you see our arms correspond to the fore legs of beasts, though we never use them for moving about, except when we go on our hands and knees, or climb trees, or swim in the water. And as for birds--why, their fore limbs are turned into wings, to fly with, so that they walk or hop on their hind limbs only, just as we do. Animals that go on all fours are called _quadrupeds_. Animals that go on their two hind limbs only, like Bird People and House People, are called _bipeds_. A Sparrow's wings are just as much like a mouse's fore legs, as a Sparrow's feathers are like a mouse's fur."

"How funny!" said Dodo. "But how are a bird's wings like fore legs, when they haven't got any paws or toes--or fingers--or claws--only just long feathers?"

"They have fingers, and some birds' wings have claws; only you cannot see them, because they are all wrapped up in the skin and covered over with the feathers. Some day--not to-day, because you have had a long lesson already--I will show you a bird's wing with only its bones. Then you will see that it has finger-bones at the end, then hand-bones next, then bones that run from the wrist to the elbow, and then one bone that runs from the elbow to the shoulder--almost the same bones that people have in their fingers, hands, wrists, and arms. So you see wings are the same to a bird that fore legs are to a mouse or arms are to us.

"I could go through all the inside parts of birds, and show you something like the same parts in people,--stomach and bowels, to take care of the food they eat and turn it into blood to nourish them; lungs to breathe with, and keep the blood pure; heart to beat and thus pump the warm blood into all parts of the body; brain and nerves, which are what birds think and feel with, just as we do with ours; and all their bones, which together make what we call the _skeleton_, or framework of the body, to keep the flesh in shape and support the other organs."

"Dear me!" sighed Dodo; "there must be ever so many more things inside of birds that we can't see, than there are outside."

"Of course there are!" said the Doctor. "It won't be very hard for you to remember the outside parts, and learn the names of them all. I have told you most of them that you need to remember, to understand the stories I am going to tell you about birds. See here! What do you think of this?"

So saying, the Doctor unrolled a large sheet of drawing-paper that hung on the wall. "Here is a picture of the White-throated Sparrow, drawn so big you can see it almost across the room, with all the outside parts of which you must learn the names. You see the names are all on the picture, too; I am going to make it smaller, and put it in the book I will write for you, so you can look at it whenever you wish.

"It is almost dinner-time now, and you must be very hungry. But now I must tell you one thing more. You know there are so many, many different kinds of birds and other animals that nobody could remember them unless they were classified. To classify is to put things that are most alike closest together, then next nearest them things that are next most alike, and to keep furthest apart those things that are least alike. Now it is true that all beasts, birds, snakes, lizards, frogs, and fishes have some things alike, though each has some other things different from all the rest. If they were not all alike in some things, we could not call them all animals. One of the things in which all the animals I have named are alike is, that they all have skeletons. One of the things in which all their skeletons are alike is, that they have backbones. Backbones are the chains of bones that run along the back from the head to the tail. Backbones are called by the Wise Men _vertebrae_; animals that have backbones are named _Vertebrates_; and animals that lack backbones are named _Invertebrates_."

"Tell us the names of some Invertebrates, please, Doctor," said Rap.

"Well, all sorts of insects are Invertebrates, and so are lobsters and crabs, oysters and clams, worms, starfishes, jelly-fishes, corals, and even sponges. Then there are some too small to see without a microscope. But never mind about Invertebrates now. I only want you to remember that all beasts, birds, reptiles, and fishes are Vertebrates, and that there are five principal classes of them. If I should tell you as much about them as I have about the Building of a Bird, you would see that they are all built on what we call the Vertebrate plan of structure. Here is a chart of the Classes of Vertebrates--you can study it this afternoon, till you learn it by heart."

VERTEBRATES

_Animals with Backbones_

CLASS I. Mammals.--Warm-blooded animals which have fur or hair, bring forth their young alive, and nurse them. House People are Mammals.

CLASS II. Birds.--Warm-blooded animals which have feathers and lay eggs.

CLASS III. Reptiles.--Cold-blooded animals which have scaly skins, like lizards, snakes, and turtles.

CLASS IV. Batrachians.--Cold-blooded animals which have naked skins, like frogs, toads, and newts.

All the foregoing classes, except a few of the Batrachians, breathe air in lungs, and almost all, except snakes, have legs; none now living can fly, except bats and birds; but bats are Mammals.

CLASS V. Fishes.--Cold-blooded animals which have either scaly or naked skins, but no fur or feathers; which live in the water, breathe it with their gills, and swim in it with fins.