CHARACTERS AND HABITS OF BIRDS RELATED TO USE
=Feathers.= The feathers of a bird are the most highly developed form of
protective covering in animals, serving other important functions in
addition to the primary one. Compared with the hair of a mammal or the
scale of a fish or of a reptile, a typical soft feather from the body of
a bird is a very complex structure, partaking of the characters of both
scales and hair. The fact that birds have scales and hair as well as
feathers shows their relation to these other forms of animal covering.
This is best observed on a fowl. The legs of a fowl are normally smooth,
with scales on the front of the shank and on the upper surfaces of the
toes. In feather-legged fowls the feathers appear first along the outer
sides of the shanks and toes. As the number of feathers is increased
they grow longer and more feathers appear, until in the most heavily
feathered specimens the soft skin is covered and the scales are almost
hidden.
The face of a fowl is normally almost bare, the skin being a bright red
like the comb and wattles; but at a distance of a few feet we can
usually see some very small, fine feathers on it, and if we examine
closely we see in addition still finer growths--hairs. Among the body
feathers of a fowl, too, are quite long hairs. These are most easily
observed after a bird is plucked. They do not come out with the
feathers, and are removed by singeing.
=Structure of feathers.= The smallest feather that to the naked eye
appears as something more complex than a hair, looks like a little bunch
of fuzzy filaments. This is called down.
In the next higher form of feather a small round quill appears with
filaments protruding from it like the hairs in an artist's brush. Such
a feather is called a stub feather, or simply a stub. The best place to
find these is on the outside of the shank of a fowl with scantily
feathered legs.
The first form of the complete feather is best observed either on the
head of a fowl or at the hock joint. The feathers in these places are
very small, yet complete. The round quill is lengthened into a shaft.
Extending from each side of this shaft is a single row of filaments,
called barbs, the edges of which, interlocked with little hooks, form
the web of the feather. On other parts of the body of the bird the
feathers are larger, but the general structure is always the same. The
size and special structure of the feather are always adjusted to suit
the part on which it grows or the service which it has to perform.
As the first function of the feathers is to keep the bird dry and warm,
the body feathers are all soft as compared with the large stiff feathers
of the wings and tail; yet as we look at the feathers on different parts
of the body of a bird we notice differences in their structure, and also
notice that the structure of a feather is not always the same throughout
its length. On the exposed parts of the feathers of the neck, back,
wings, and breast the web is perfect and the feathers overlap so closely
that they present a smooth surface. Under the surface, especially next
the skin, the barbs are not smoothly joined, but are fluffy. Thus the
same feathers which present a hard, smooth surface to the weather
provide a soft, warm garment next the skin. Under the wings and on the
underside of the body the feathers are quite fluffy throughout their
whole length.
=Arrangement of the feathers.= As you look at a living bird the feathers
appear to grow on all parts of the body. When the feathers are removed
from the bird you see that while the skin is nearly all rough, with the
little elevations where the feathers were removed, there are quite large
areas where the skin is perfectly smooth, showing that no feathers grew
there. These places are bare because feathers on them would interfere
with the movements of the bird. The feathers on adjacent parts give the
smooth areas sufficient protection.
=Decorative feather forms.= The natural decorative forms of plumage are
found mostly in male birds and consist of extraordinary developments of
the plumage of the neck and back, where the male birds of some species
always have feathers differing in form from the feathers on the same
parts of the female. When a feather appendage not common to a species is
developed on some varieties, as the crest and beard on fowls and the
ruff on pigeons, both sexes have it. The most interesting feather
decorations will be described particularly in the chapters on the
species on which they occur.
[Illustration: Fig. 1. Brown Leghorn chick (one day old)]
=Color in feathers.= While colors in the plumage are distributed very
differently in different species of birds, often making combinations
peculiar to a species, there is in all the same wonderful formation of
patterns, that depends for its effect in a section upon some overlapping
feathers being marked alike and others having a different marking; and
for the effect in a single feather, upon adjacent barbs being now alike,
now different, in the distribution of the pigment in them. The best
common example of a pattern covering a series of feathers is found on
the wing of a Mallard Duck or of a Rouen Duck. Interesting examples of
the formation of patterns on a single feather may be found in the
plumage of barred, laced, and penciled fowls, and also in the lacings on
the body feathers of the females of the varieties of ducks mentioned.
Perhaps the most interesting illustrations of this kind, however, are to
be seen on the plain feathers of the guinea and the gorgeous tail of the
peacock.
The pigment which colors the plumage may be found in soluble form in
the quills of immature colored feathers. It is not conspicuous unless it
is quite dark. In black fowls it is often so abundant that a part
remains in the skin when the feathers are removed. After the pigment is
deposited in the web of the feather the color is fast. Water does not
affect it, but it fades a little with age and exposure. New plumage
usually contains a great deal of oil, a condition which is most
conspicuous in white birds, to whose plumage the oil gives a creamy
tint. In colored birds the presence of a large amount of oil in feathers
is desirable because it gives greater brilliance to the plumage.
[Illustration: Fig. 2. White Leghorn chicks (ten days old)]
=Growth and molting of feathers.= The first covering of a young bird is
down. The young of birds which nest on the ground have the down covering
when hatched; others acquire it in a few days. In small land birds which
feather quickly, as Leghorn and Hamburg chicks, the largest wing
feathers may have started to grow before the chick leaves the egg. In
most kinds of poultry, however, the young show no signs of feathers for
some days. The down is gradually replaced by small feathers, and these
by larger feathers as the bird grows. As feathers in all stages of
growth are found on the young bird at the same time, it is not known
whether all feathers are molted the same number of times. In cases where
some feathers were marked and watched, or where the colors changed with
the changing feathers, it appeared that after the down three sets of
feathers were grown in succession, the third and last making the adult
plumage of the bird. This coat remains until the following summer or
fall, when it is molted and replaced by a new one.
=Flight.= The habit of flying is objectionable in domestic birds because
it makes them more difficult to control. It has no direct use except in
pigeons kept for flying. There is, however, a very important connection
between development for flying and the value of birds for the table. The
muscles of the wings furnish the greater part of the edible meat of most
birds. The most desirable birds for food purposes are those which have
the wing muscles well developed, yet not quite strong enough to enable
them to fly easily. In such birds the breast meat remains comparatively
soft through life, while in birds that fly well it becomes hard in a
very short time. That is why the breast meat of the pigeon is relatively
tougher in an old bird than the breast meat of a fowl or turkey.
The balance between capacity for flight and neglect to use it, which is
desired in birds grown for the table, is secured by giving them
opportunity to exercise their wings moderately but not for progressive
practice in flying, which would soon enable them to fly easily over the
fences used to confine them. To regulate such exercise the perches for
birds that roost are made low, or in an ascending series in which each
perch after the first is reached from the one below it, while fences are
made so much higher than the distance the bird is accustomed to fly that
the failures of its first efforts to go over them discourage it. Ducks
and geese, which do not roost, flap their wings a great deal, and if
they have room often exercise them by half running and half flying along
the ground.
=Mechanism of the wing.= In its structure and in the muscular power that
moves it, the wing of a bird is a wonderful piece of mechanism. A bird
in flying strikes the air with its wings so rapidly that the movements
cannot be accurately counted. The heron, which is a slow-flying bird,
makes from one hundred twenty to one hundred fifty downward strokes of
its wings a minute. As each downward stroke must be preceded by an
upward stroke, this means that the wings make from two hundred forty to
three hundred separate movements a minute. In such swift-flying birds as
the pigeon the movements of the wings can be distinguished but cannot be
counted. The fastest movements of the wings are not made by the swiftest
fliers. In order to fly at all some land birds with comparatively small
wings have to move them so fast that the movements make a blur and a
whirring noise. The partridge is an illustration of a bird of this
class.
If the supporting surface of the wing of a bird were made of skin, like
the web of the foot of a swimming bird, it would be necessary to fold
the wing for each upward stroke. It is here that the structure of
feathers adapts itself to the rapid action required for movement in the
air. The wing is not one surface but a series of narrow surfaces lapping
in such a manner that they unite to form one broad surface when the
downward stroke is made, and with the upward stroke are separated so
that the air passes between them. Greater power in the downward stroke
and less resistance in the upward stroke are also secured by the
curvature of the wing. The under side is concave, the upper side convex.
Thus in the downward stroke the wing gathers the air under it and so
increases the pressure, while in the upward stroke it scatters the air
and reduces the pressure.
If the wing were equally rigid throughout, the movement of the bird
would be mostly upward. The bird in flying moves forward because the
front of the wing is rigid and the tips of the feathers, which are
directed backward, are flexible. So the air compressed by the wing in
the downward stroke escapes backward, and in doing so propels the bird
forward. The principle is the same that is applied in the screw
propeller of a boat or an airship, except that the wing vibrates while
the propeller revolves.
The most important function of the tail in flight is to balance the
bird. It is of some assistance in steering, but a bird steers its course
mostly by manipulation of the wings.
=Scratching.= With the exception of the aquatic birds and the ostrich,
all the species of poultry belong to the group called by naturalists
_Rasores_ or _Scratchers_. Birds of this class have legs of moderate
length and very strong, with toes terminating in a stout claw. Normally
they have three toes upon which the foot rests when they are standing on
a flat surface, and a fourth toe, like a thumb, which assists the other
toes to grasp a perch. Some individual birds and some races of birds
have the fourth or hind toe double. The leg of a bird is so constructed
that when it is bent as the bird sits on a narrow support the toes
contract and grasp the support and hold it without any effort on the
part of the bird. Thus the bird is as secure in its position on a limb
when asleep as if wide awake and looking out for itself.
In proportion to their ability to scratch, birds are able to find seeds
and insects concealed among dead or living vegetation on the surface of
the ground, and also to dig below the surface. Scratching capacity is
most highly developed in the fowl. Compared to it the other land birds
are very feeble scratchers, and do little damage by scratching if free
to roam about. For ages the scratching propensity of fowls was regarded
as a vice in them, but since people began to give special attention to
poultry they have learned that fowls are much more contented and thrifty
in confinement if their food is given them in a litter of leaves, straw,
or shavings, in which they must scratch for it, and have also found that
to some extent fowls may be used to cultivate crops while destroying
insects and weeds among them.
=Swimming.= Capacity for swimming has an economic value in domestic
birds because it adapts those possessing it to places which land birds
rarely frequent. It will be shown when the different kinds of aquatic
birds are described that each has its special place and use in
domestication.
The swimming faculty in these birds is of further interest because of
its relation to the development of the body plumage. If a land bird is
placed in the water, the feathers are quickly saturated, the water
penetrating to the skin. A duck or other swimming bird will remain in
the water for hours without the water penetrating the feathers. This is
commonly supposed to be due to the presence of a large amount of oil in
the feathers, but the difference in the oiliness of the feathers of
fowls and of ducks is not great enough to account for the difference in
resistance to the penetration of water. The peculiar quality of the
plumage of swimming birds is its density. If you take up a fowl and
examine the plumage you will find that it is easy to part the feathers
so that the skin can be seen. It may be done with the fingers, or even
by blowing gently among the feathers with the mouth. Now try to separate
the feathers of a duck so that the skin will be visible. You find it
much harder, because the feathers are so thick and soft and at the same
time so elastic. The familiar phrase "like water from a duck's back" is
not especially appropriate. The feathers on the back of most birds are a
very effective protection against rain. The feathers all over a duck are
such poor conductors of water that it is hard to remove them by
scalding. The structure of the plumage of swimming birds adds to their
buoyancy in the water. They do not have to exert themselves to remain on
the surface, but float like cork.
=Foods and mode of digestion.= All kinds of poultry and most of our
common wild birds are omnivorous eaters, but the proportion of different
foods usually taken is not the same in different kinds of birds. Some
eat mostly grains, some mostly animal foods. Some can subsist entirely
on grass if they can get it in a tender state; others eat very little
grass. The scratching birds like a diet of about equal parts of grain,
leaves, and insects. Pigeons and canaries live almost entirely on grains
and seeds, but like a little green stuff occasionally.
Domestic birds which produce many eggs require special supplies of food
containing lime to make the shells. Until within a few years it was
universally believed--and it is still commonly supposed--that birds
needed grit to take the place of the teeth nature did not give them, and
assist in the grinding of the food in the gizzard. Many close observers
now reject this idea because they find that birds supplied with
digestible mineral foods do not eat those that are not digestible. A
bird does not need teeth to grind its food, because it is softened in
the crop and the gastric juice acts upon it before the grinding process
begins.
=Peculiarities of birds' eggs.= The only animal foodstuff produced in a
natural package, easily preserved and handled, is the egg. In the
vegetable world we have a great many such things--fruits, seeds, roots,
nuts, with coverings of various textures to protect the contents from
the air. In all of these the material stored up is either for the
nourishment of the seeds in the first stages of growth as plants, or for
the nourishment of a new or special growth. An egg is the seed of an
animal. All animals produce eggs, but in mammals the new life
originating from the egg goes through the embryonic stages within the
body of the parent, while in insects, fishes, reptiles, and birds the
egg is laid by the creature producing it before the embryo begins to
develop.
In mammals the embryo grows as a part of the body of the parent, the
substances which build it up coming from the parent form as they are
needed. In birds a tiny germ--the true egg--is put, with all the
material needed for its development as an embryo, in a sealed package,
which may be taken thousands of miles away from the parent, and, after
lying dormant for weeks, may begin to grow as soon as the proper
conditions of temperature are applied. The food value of the germ of an
egg is inappreciable. We use the egg to get the material stored up in it
for the young bird which would come from the germ.
=Development of the egg.= The method of the formation of an egg is very
interesting. It is the same in all birds, but is most conveniently
studied in fowls. If a laying hen is killed and the body is opened so
that the internal organs can all be seen, one of the most conspicuous of
these is a large, convoluted duct having its outlet at the vent. In this
duct, which is called the oviduct, are eggs in various stages of
formation. At its upper extremity, attached to the backbone, is a bunch
of globular yellow substances which are at once identified as yolks of
eggs in all sizes. The organ to which these are attached is the ovary.
The smallest yolks are so small that they cannot be seen without a
powerful microscope. These yolks are not germs, but as they grow the
germ forms on one side of each yolk, where it appears as a small white
spot.
When a yolk is full-grown it drops into the funnel-shaped mouth of the
oviduct. Here it is inclosed in a membranous covering, called the
chalazae, and receives a coating of thick albumen. The function of the
chalazae is to keep the yolk suspended in the center of the egg. It does
not merely inclose the yolk, but, twisted into cords, extends from
either end and is attached to the outer membrane at the end of the egg.
After leaving the funnel the egg passes into a narrow part of the
oviduct, called the isthmus, where it receives the membranous coverings
which are found just inside the shell. From the isthmus it goes into the
lowest part of the oviduct--the uterus. Here the shell is formed, and at
the same time a thin albumen enters through the pores of the shell and
the shell membranes and dilutes the thick albumen first deposited. After
this process is completed the egg may be retained in the oviduct for
some time. It is, however, usually laid within a few hours.
=Rate and amount of egg production.= In the wild state a bird, if not
molested after it begins laying, produces a number of eggs varying in
different kinds, according to the number of young that can be cared for,
and then incubates them. If its first eggs are removed or destroyed,
the bird lays more, usually changing the location of its nest. In
domestication the eggs of most kinds of birds are removed from the nests
daily as laid, and the birds lay many more eggs before they stop to
incubate than they do in the wild state.
It is, and has been for ages, the common opinion that the wild birds and
poultry, when first domesticated, were capable of laying only a small
number of eggs each season, and that laying capacity has been enormously
increased in domestication; but the oldest reports that we have of the
amount of egg production indicate that the laying capacity of fowls was
as great centuries ago as it is at the present time. Recent observations
on wild birds in captivity show that even birds which pair and usually
lay only a few eggs each season have a laying capacity at least equal to
the ordinary production of hens. Quails in captivity have been known to
lay about one hundred eggs in a season, and an English sparrow from
which the eggs were taken as laid produced over sixty.
The constitutional capacity to produce ovules is now known to be far
greater than the power of any bird to supply the material for the
nourishment of germs through the embryonic stage. The principal factors
in large egg production are abundance of food and great capacity for
digesting and assimilating it.
=Incubation.= A bird before beginning to lay makes a nest. Some birds
build very elaborate and curious nests; others merely put together a few
sticks, or hollow out a little place on the ground. In birds that pair,
the male and female work together to build the nest. Even in polygamous
domestic birds like the fowl and the duck, a male will often make a nest
for the females of his family and coax them to it as a cock pigeon does
his mate.
If the birds are left to themselves and the eggs are not molested, an
aerial bird will usually lay a number of eggs equal to the number of
young the parents can feed as long as they require this attention, while
a terrestrial or aquatic bird will usually lay as many eggs as she can
cover. The desired number of eggs having been laid, the process of
incubation by the parents begins.
The incubation of their eggs by birds is one of the most remarkable
things in nature. We say that "instinct" leads birds to build their
nests and to keep their eggs warm for a period varying from two weeks
for small birds, to six weeks for the ostrich; but "instinct" is only a
term to describe the apparently intelligent actions of the lower
animals, which we say have not intelligence enough to know the reasons
for the things that they do.
[Illustration: Fig. 3. Sitting hen]
The mother of a young mammal knows that it came from herself, and she
can see that it is like her and others of her kind. It at once seeks her
care and responds to her attentions. The egg which a bird lays is as
lifeless--to all appearances--as the stones which it often so closely
resembles. Only after many days or weeks of tiresomely close attention
does it produce a creature which can respond to the care lavished upon
it. The birds incubating eggs not only give them the most unremitting
attention, but those that fill their nests with eggs before beginning to
incubate methodically turn the eggs and change their position in the
nest, this being necessary because otherwise the eggs at the center of
the nest would get too much heat and those at the outside would not get
enough. A bird appears to know that if she begins to sit before she has
finished laying, some of the eggs would be spoiled or would hatch before
the others; and, as noted above, aerial birds seem to know better than
to hatch more young than they can rear. But no bird seems to have any
idea of the time required to hatch its eggs, or to notice the lapse of
time, or to care whether the eggs upon which it sits are of its own
kind or of some other kind, or to know whether the young when hatched
are like or unlike itself. If eggs fail to hatch, domestic birds will,
as a rule, remain on the nest until the eggs are taken away or until
sheer exhaustion compels them to abandon the hopeless task. In
domestication, however, those birds which continue laying most freely
when their eggs are removed as laid, tend to lose the habit of
incubation. Turkeys and geese will often begin to incubate after having
laid about the number of eggs that they could cover. Many fowls will do
the same, but most fowls lay for several months before attempting to
incubate, and in many races not more than two or three per cent of the
hens ever incubate.
[Illustration: Fig. 4. Fresh egg[1]]
[Illustration: Fig. 5. Infertile egg (after twenty-four hours'
incubation)]
[Illustration: Fig. 6. Fertile egg (after twenty-four hours'
incubation)]
[Illustration: Fig. 7. Embryo (after seventy-two hours' incubation)]
[Illustration: Fig. 8. Embryo (after seven days' incubation)]
[1] Photographs (Figs. 4-8) from Bureau of Animal Industry, United
States Department of Agriculture.
[Illustration: Fig. 9. Chick ready to break shell]
=Development of the embryo in a bird's egg.= The condition required to
produce a live bird from a fertile egg is the continuous application of
a temperature of about 102 or 103 degrees Fahrenheit from the time the
heat is first applied until the embryo is fully developed and ready to
emerge from the shell. In nature the heat is applied by contact with the
bodies of the parent birds. Development of life will start in an egg at
about 10 degrees below the temperature required to maintain it, but at
this temperature the germ soon dies. The temperature in incubation may
occasionally go higher than 103 degrees or may be as low as 70 degrees
for a short time without injury to the germ. Some germs will stand
greater extremes of temperature than others, just as some living
creatures will.
The first stages of the development of life in the egg of a bird may be
observed by holding the eggs before a strong light in a darkened room.
White-shelled eggs are the best for this purpose. In about thirty-six
hours from the beginning of incubation it will be found that the germ
has turned red, and little red veins radiate from it somewhat like the
legs of a spider. For several days the egg is quite translucent and the
yolk shows plainly. As the germ grows, the contents of the egg become
clouded and dense, and the air space at the large end of the egg is
clearly defined, the density being greatest near it. From the time that
the egg becomes dense, observations of development must be made by
breaking one or more eggs daily or every few days, according to the
number available for observation.
[Illustration: Fig. 10. Egg before exclusion and partially excluded
chick]
[Illustration: Fig. 11. Light Brahma (day old)]
The embryo grows until it fills the egg. The mere application of heat to
the egg has gradually transformed that little germ and the yellow and
white of egg into bones, flesh, skin (and, in some cases, down), and all
the organs of a living creature. When the embryo has filled the shell,
it lies curled up, usually with the head at the large end of the egg and
the beak almost touching the shell, at about one third of the distance
from the large to the small end of the egg. At the point of the beak of
the young bird on the curved tip of the upper mandible is a small horny
scale. Without this scale it would be hard for the embryo to break the
shell because it cannot, as it lies, strike it a direct blow with the
point of its beak. This scale is a remarkable character. Its only use is
to help the bird out of the shell. A few days after exclusion it
disappears.
If you take a hen's egg about the eighteenth or the nineteenth day of
incubation and hold it closely in your hand, you may be able to feel the
chick move. If your hand is a little bit cold, the chick is much more
likely to squirm in the egg and may utter a peep. If, with the egg in a
warm hand, you hold it to your ear, you will about this time hear an
occasional tap, tap, caused by the chicken striking its beak against the
shell. The tapping is kept up more or less steadily until the shell
cracks where the point of the beak strikes it and a little piece is
broken out. The chick usually rests awhile now,--perhaps for some
hours,--then resumes the attack on the shell. It turns in the shell,
breaking out little pieces as it turns, until there is a crack nearly
all the way around, when, by pushing with its head and feet, it forces
the shell apart and sprawls out of it.
The process is the same for all birds, except that those that take
longest to develop in the shell take a longer rest after first breaking
it. The young of aerial birds, which are naked when hatched, are ugly
little things. Young poultry, too, are almost repulsive with their
sprawling forms and the wet down plastered to the skin, but in a few
hours they grow strong, the down dries and becomes fluffy, the bright
little eyes seem to take in everything, and they are the most attractive
of all baby animals.