We were some time ago both delighted and astonished by the performances
of a German artist, who imitated with wonderful exactness the notes of
a variety of birds. The song of the nightingale and the warblings of
the skylark, the whistling of the throstle and the out-poured melody
of the canary, were gone through with such perfect execution, that the
birds themselves, we thought, could scarcely have detected a flaw in the
performance. This gifted individual introduced himself to his audience
by a somewhat humorous account of the manner in which he had acquired
his extraordinary powers. He told us that his father, who was a breeder
of birds, had upon one occasion gone from home, leaving a bag of rice
as provision for his children, and a quantity of bird-seed for his
feathered protégés. By some mistake the rice had been given to the birds,
and the bird-seed to the children, the consequence being, that on the
gentleman's return he found his birds all dead, and his children singing
like piping bullfinches. How far this explanation was satisfactory we
will not stop to inquire; but we have sometimes been almost tempted to
suppose that some similar accident must be of frequent occurrence in
Germany. The deep acquaintance of the ornithologists of that country with
the objects of their study, and the fidelity with which they note down
the minutest incidents connected with the history of their favourites,
surpassing anything achieved by other naturalists, not even excepting
such enthusiastic labourers as Wilson and Audubon, demands our warmest
praise; while the patient industry, so conspicuous in their writings, at
once calls for and excites our admiration.
Among the foremost of his countrymen in the cultivation of ornithological
research stands the author of the magnificent work whose pages it is our
wish to lay before English readers. Not content with studying the natural
history of his favourites from books, or even in the rich scientifically
arranged collections contained in so many Continental museums, his zeal
led him to follow them even into their own wild retreats, and, gun
in hand, to penetrate the burning deserts of Eastern Africa, and the
equally inhospitable, and then but little known, regions of Abyssinia.
By thus familiarising himself with the habits of birds in their native
haunts, and amid the scenery whereby they are surrounded in a state of
nature, he has been enabled to impart a freshness to his descriptions as
characteristic of the real naturalist as the smell of new-made hay is
redolent of fields and hedgerows, and no more to be imitated by the mere
compiler than the voice of an orator by the reporter of his speeches.
Before, however, we permit our author to speak for himself, it may
perhaps be desirable to preface his remarks by a few general observations
concerning the structure of the beautiful creatures that form the
subjects of his teaching, inasmuch as it is obviously desirable to have
clear notions concerning the machinery employed before its adaptation to
its intended uses can be made manifest; and further, because in the study
of ornithology, as in every other branch of natural history, there are
certain conventional terms that may require explanation before the words
used in describing an object are intelligible to the uninitiated.
The Bird is an inhabitant of the air in the fullest sense of the
expression. The atmosphere is emphatically the sphere of its activity; it
mounts it as it would a ladder; it sails through it in triumph, and rides
upon the winds as upon a fleet steed. Moreover, it is the atmosphere
itself which endows the feathered Ariel with such capabilities, and
it is in the perfection of his respiration that we must search for an
explanation of his wonderful achievements.
[Illustration: Fig. 1.--RESPIRATORY APPARATUS OF A FOWL.
_a_, the Lungs, immovably fixed; _c_, _d_, the Breast-bone, moving as
upon a hinge at _b_, so that it can be raised to the position indicated
by dotted lines at _h_. 1, 2, 3, 4, 5, 6, Cells, with membranous walls,
into which the air is freely admitted during the act of inspiration.]
The muscular activity of every animal is intimately dependent upon the
efficiency of its breathing apparatus, upon the freedom with which
the vital element finds admission to the blood which it is destined
to renovate, and upon which it confers those qualities so inseparably
connected with the elimination of increased temperature, and the vigour
of muscular action. In this respect, as we shall see immediately, the
feathered races surpass all living creatures, with the exception,
perhaps, of the members of the insect creation.
The lungs of a bird are not suspended, like those of a quadruped, within
a circumscribed chest or thoracic cavity, in such a manner as to become
inflated by each inspiration; they are rather to be described as soft,
porous, and highly vascular organs, through which the air passes as
through the interior of a sponge. The movements of the chest, upon which
depend the inspiration and expiration of the atmospheric fluid, may be
compared to those of a bellows continually employed in taking in and
expelling the surrounding element by a mechanism represented in the
accompanying figure (Fig. 1). The framework of the chest, consisting
of the ribs and of the breast-bone, is so put together that at each
inspiration it can be raised, as shown in the drawing, from the position
_d_ to the position _h_, thus materially enlarging the thoracic chamber,
just as the upper board of an ordinary bellows is raised for the purpose
of taking in the air; but, in this case, the surrounding element, instead
of entering through a valve-defended orifice, rushes down the windpipe,
and through the immovable, sponge-like lungs, permeating the wide
passages with which they are perforated, and not only filling the entire
thorax, but penetrating into the interior of the very bones, which are
left marrowless for its reception.
The mechanism whereby expiration is effected is equally simple; just as,
when the upper board of the bellows is depressed, the air is forced out
through the nozzle, so, by the return of the breast-bone to its former
position, the inspired air is again forced to pass through the lungs and
make its escape by means of the windpipe. By this process it is obvious
that the vital element--the oxygen of the atmosphere--being admitted to
every part of the system, the blood is vitalised to the greatest possible
extent, its temperature is raised until the heat of the body of a bird
is far greater than that of an ordinary quadruped, and its vitality is
proportionately exalted. Consequently, as the blood circulates through
the system, it carries with it heat and life in superabundance; the
energies of the entire system are roused to the uttermost; the fibres of
every muscle quiver with intense life, like a steam-engine working under
high pressure, thus enabling the falcon to cleave the skies with the
velocity of a falling thunderbolt, and not only qualifying the swallow
for its rapid flight, but enabling it to achieve its wonderful migrations.
This admission of air into every part of the system serves not only
to fan the vital flame, and rouse the energies of the bird to an
extraordinary degree of tension; it likewise assists in giving buoyancy
to its movements, bearing it upward, as the gas does a balloon; for it is
evident that the air received into the body being raised to a temperature
corresponding to the heat of its blood, the specific gravity of the
bird is proportionately diminished, and it rises into the air almost
without an effort, and even hovers in the sky with scarcely a perceptible
movement of its wings.
A knowledge of the mechanism of their mode of respiration will likewise
enable us to explain another remarkable feature in the history of the
feathered tribes, namely, their power of song. Who that has listened to
the prolonged warblings of a linnet, the flood of melody poured forth
from the little throat of the canary, the "lengthened sweetness long
drawn out" which almost pains the enraptured ear as we listen to the
song of the nightingale, but has wondered how such tiny birds can ever
find sufficient breath for the utterance of such long-sustained, such
interminable notes? What would our prima-donnas at the opera give for but
the tithe of the capacity of these favoured little songsters? No human
breast could ever hold sufficient breath for such performances. We now
see, however, that the vocal organs of a bird are exactly adapted to
the nature of their music. Their whole body is a bellows, as large in
proportion to their size as the bellows of an organ is in relation to the
pipes into which it has to pour the sound. The little bird is, in fact,
a living harmonium--its singing apparatus is not situated at the top of
its throat, but is implanted in the inferior termination of its windpipe;
and just as the tongue of the harmonium is thrown into vibration by the
issuing current of air caused by pressure upon the bellows, so are the
vocal chords of the feathered songster rendered sonorous as the air
passes over them. In proportion to the capacity of the bellows must be
the duration of the note, and we have already seen that the air-cells of
the bird are capable of furnishing a supply not easily exhausted. There
is, however, this remarkable difference between the two instruments:
the tongue of each key of the harmonium can give utterance but to one
sound--one never-varying tone--while the corresponding part of the
bird, rendered more or less tense by muscles provided for the purpose,
contains within itself a whole gamut, and there is not a note in the
scale that is not instantly at the command of the inimitable little
musician. In the perching birds, among which are found by far the most
accomplished singers, five pairs of muscles are connected with this
exquisitely-contrived apparatus, and are so disposed as to influence
both the diameter and the length of the air-passages. In the parrots
three pairs are met with; some of the swimming birds have two, while
others have only one; and in a few--as the king of the vultures and the
condor--vocal muscles are quite wanting.
Seeing that the temperature of birds is raised so much above the usual
standard by the arrangements described above, some clothing is requisite,
adequate to retain the vital heat. Another indispensable provision is
therefore met with in the FEATHERS with which all birds are so warmly
clad. Indeed, so peculiar is the texture of these admirable fabrics,
that no better distinctive appellation could be devised for the entire
class than that of the "feathered tribes," by which they are frequently
designated. A feather realises in its structure more qualities than
imagination could have conceived it possible to combine--lightness,
thickness, warmth, durability, elasticity, softness, strength, and
beauty. It is one of the master-works of creation. Whoever has examined a
feather under the microscope will testify to the incomparable perfection
of the contrivance. Every feather is a mechanical wonder. If we look at
the quill-portion, or barrel, we find it possessed of attributes not
easily brought together--strength and lightness. If we cast our eye upon
the upper part of the stem, we see a material made for the purpose,
which is used in no other class of animals, and in no other part of
birds--tough, light, pliant, elastic--the pith. This is also a substance
_sui generis_; it is neither bone, flesh, membrane, nor horn.
[Illustration: Fig. 2.--WING OF A BIRD PARTIALLY STRIPPED OF FEATHERS, TO
SHOW THE INSERTIONS OF THE QUILLS.
_a_, the Arm; _d_, the Fore-arm; _g_, the Thumb; _c_, the Secondary
Quills, implanted into the Fore-arm; _f_, the Primary Quills, implanted
into that portion of the Wing which represents the hand; _e_, the
Spurious or Bastard Quills, derived from the Thumb.]
But the most wonderfully constructed part of a feather is the _plume_,
or, as it is sometimes called, the _web_. This is affixed to each side of
the stem, and constitutes the broad expansion of the feather, that part
which we usually strip off when making a pen. One of the first things to
be remarked is that the web is much stronger when pressed in a direction
perpendicular to the flat plane of the plume than when rubbed either up
or down in the direction of the stem; the reason of this is that the
web is composed of numerous flat, thin, and broad laminæ, arranged with
their flat sides together, so that, although they easily bend towards
each other, they offer great resistance in the direction in which they
have to encounter the impulse and pressure of the air; and it is in this
direction only that their strength is wanted and put to the test.
Another particularity is still more admirable. Whoever examines a feather
cannot help noticing that the laminæ of which we have been speaking,
in their natural state seem to be fastened together. Their adhesion to
each other is manifestly something more than mere apposition; they are
not to be separated without a certain degree of force, and, as there is
evidently no glutinous cohesion between them, it is plain that by some
mechanical means or other they catch or clasp among themselves, thereby
giving to the web its closeness and compactness of texture. Nor is this
all. When two laminæ which have been separated by accident or design
are brought together again, they immediately reclasp; the connection,
whatever it was, is perfectly restored, and the web of the feather
becomes as smooth and firm as if nothing had happened to it. Draw your
finger down the feather, which is, so to speak, against the grain, and
you will probably destroy the junction between some of the contiguous
laminæ; draw your finger up the feather in the opposite direction, and
you restore all to their former state of coherence. This is no common
contrivance. Let us now inquire concerning the mechanism whereby it
is effected. The laminæ above mentioned, examined individually, are
found to be provided with vast numbers of long fibres, or teeth, which
project from their edges in such a manner that, when placed in contact,
those of contiguous laminæ hook and grapple together. The fibres are
extremely minute; indeed, fifty of them have been counted by means of
the microscope in the space of the 1/20th of an inch. Every fibre is
crooked, but bent after a definite manner; those that proceed from one
edge of a lamina are long, flexible, and bent downwards, whereas those
that proceed from the opposite edge are shorter, firmer, and turned
upwards. The manner in which they are united is, therefore, as follows:
When two contiguous laminæ are pressed together, so that the long fibres
are forced far enough over the short ones, their crooked parts fall into
the angles formed by the crooked parts of the others, just as the latch
of a door falls into the cavity of the catch fixed to the door-post, and
there hooking itself, fastens the door. This admirable structure, which
may be readily seen with a very ordinary microscope, ensures not only
the union of the laminæ, but renders it possible that when any two of
them have been separated by violence they will become re-connected with
facility and expedition. In the ostrich, this apparatus of crotchets and
fibres, of hooks and eyes, is wanting; the filamentary laminæ hang loose
and separate, forming a kind of down; but such a plan of construction,
however it may fit the plumes for the flowing honours of a lady's
head-dress, must be considered as detrimental to the bird, inasmuch as
wings composed of such feathers, although they may assist in running,
will not serve for flight.
[Illustration: Fig. 3.--NASCENT FEATHER OF A CHICKEN.
_c_, the External Horny Sheath, slit open; _d_, _d_, Web of the Feather
produced in successive layers from the central stem, _e_.]
The power of inflating their whole body with air, and the possession
of feathers, are therefore the most distinctive endowments of a bird,
inasmuch as these attributes are quite peculiar to the class.
To creatures thus gifted with strength and activity so extraordinary,
it is manifest that perceptions of great acuteness are requisite,
corresponding with the rapidity of their movements and the intelligence
necessary for the performance of the important duties entrusted to their
charge; and in this respect, as will be made manifest by a perusal of
their history, they occupy a position in the economy of nature fully
equal or even superior to that enjoyed by the most favoured quadrupeds.
The mental faculties of the parrots correspond with those of the monkeys,
whom in their habits and capabilities these birds closely resemble; in
cunning they are quite upon a par with their four-handed neighbours,
with which, in the forests of tropical countries, they are so generally
associated; and when removed from their native woods, and made, as they
often are, the companions of mankind, the facility with which they can
be taught to imitate human actions--nay, to mimic our very speech--bears
ample testimony to the exalted character of their mental capacities.
On examining the brain of a bird, the anatomist is therefore by no means
surprised to find that, both in its development and in the perfection of
its structure, it surpasses that of many quadrupeds. The proportionate
volume of the brain of some of our singing birds, as compared with the
dimensions of their body, is astonishing, and reveals to us at a glance
the reason why these little favourites are so sagacious and so eminently
susceptible of education. (See Fig. 4.)
[Illustration: Fig. 4.--HEAD OF A SWAN (_Cygnus olor_).
The upper part of the skull has been removed to show the brain and eyes
_in situ_. _a_, _a_, the Cerebral Hemispheres; _b_, the Cerebellum; _c_,
the Spinal Cord. All the above parts are represented covered by their
investing membranes. _e_, Sinuses of the Dura Mater; _g_, _g_, Walls of
the Skull; _h_, _h_, Base of the Beak; _m_, Optic Nerve of the Left Eye;
_p_, _p_, Large sentient Nerves supplying the Bill; _v_, Bony Ring in
front of the Eye-ball; _x_, _x_, Transparent Cornea; 1, 3, 5, 7, Muscles
moving the Eye-ball.]
In strict correspondence with this exalted condition of their cerebral
organisation are the senses whereby they hold intercourse with
surrounding nature. Their power of vision is beyond our comprehension,
and the elaborate contrivances whereby the eye of a bird is adapted
to its peculiar mode of life, might furnish materials for a lengthy
treatise, imperfect as is our knowledge of the numerous delicate
arrangements demonstrable by anatomical skill in every part of its
structure. At present we can but briefly allude to a few of the more
conspicuous peculiarities wherein the visual apparatus of a bird differs
from that of other creatures.
The distances from which the vulture and the hawk can see their prey
are almost incredible. To have the "eye of a hawk," to see with "eagle
glance," are expressions which, though common enough, give but a very
feeble idea of the extent to which those birds are gifted in this
respect, or of the vast expanse bounded by their horizon. The falcon sees
its diminutive prey from an altitude at which it is itself invisible,
and from the very sky swoops down upon its quarry with the velocity of a
shot, rarely missing its victim, and thus proving at once the perfection
of its sight and the steadiness of its aim. The eye of these birds must
therefore be constructed after the plan of a telescope, and its focus
adapted to long-sightedness. Its axis must be lengthened to an extent
greater than is compatible with a spherical form of the eye-ball. To
meet this requirement a circlet of bony plates, constituting a firm but
at the same time somewhat flexible ring or hoop, is introduced into
the composition of the outer coat of the eye, whereby the requisite
elongation is effected, and the organ is thus adapted for perfect vision
at a great distance. (See Fig. 4.)
The above beautiful arrangement, however, constitutes but a part of the
mechanism required. A telescope adjusted for distant vision is quite
useless when brought to bear upon an object close at hand, and its focus
must necessarily be altered in accordance with the changed conditions.
In the case of the telescope, the needful adjustment would be effected
by shortening or lengthening the sliding tube; but in the bird some
other plan is evidently indispensable, and few contrivances in animal
mechanics are more admirable than that which is adopted. Embedded in the
transparent vitreous humour of the eye is a peculiar apparatus called
the "marsupium," the texture of which resembles that of the human iris.
Now the iris, as we all know, being eminently sensitive to the intensity
of light, by its spontaneous contractions and dilatations is enabled to
alter the diameter of the pupil of the eye, and thus exactly control
the quantity of light admitted. The marsupium, equally sensitive, and
equally spontaneous in its action, swells or contracts its dimensions,
filling or emptying itself like a sponge, and thus adjusting the lenses
of the eye so as to secure perfect vision at whatever distance the object
to be seen may be placed. The quickness of sight with which birds are
gifted is equally remarkable. The swallow is proverbially one of the
swiftest flyers in the feathered creation, and yet in the full career
of its flight it is looking on the right hand and on the left, upwards
and downwards, for its food. The insects upon which it preys are often
exceedingly minute, sometimes flying above and sometimes below the level
of the swallow's course, and yet they are seen and captured without any
diminution of the prodigious rate at which the bird is flying. Nay,
more, any one who attentively watches one of these birds skimming over a
meadow, may perceive that it will capture two or even three insects in
such quick succession as to convince him that the swallow must have "had
an eye upon them" all at once, and yet they are caught, as it were, in a
moment.
[Illustration: Fig. 5.--SECTION OF THE HEAD OF AN EAGLE, SHOWING THE
STRUCTURE OF THE EYE.]
Another admirable contrivance peculiar to the feathered race, is the
existence of a thin, semi-transparent veil, which, when requisite, can
be instantaneously drawn over the front of the eye. This apparatus,
generally known as the "nictitating membrane," is useful for a variety of
purposes; it sweeps over the eye to cleanse it from dust, it diffuses the
tears which keep it bright and polished, it will act as a screen to shut
out the too great intensity of light, so that with its assistance the
eagle can confront the sun even at noon-day; it will likewise defend the
eye from sudden injuries, and yet, even when drawn like a curtain over
the pupil, not shut out the light. The commodious manner in which this
membrane lies folded up in the inner corner of the eye, and the quickness
with which it executes its purpose, are known to every observer; but what
is equally admirable, though not quite so obvious, is the employment
of two kinds of material, and the combination of two kinds of force,
by which the movements of this membrane are effected. It is not, as
in ordinary cases, by the action of two antagonist muscles, the one
pulling it forward and the other backward, but the membrane itself, being
elastic, is capable of being drawn out like a thin sheet of india-rubber,
and of returning to its former position when the force acting upon it
is removed. Such being its nature, in order to adapt it for its office
it is connected by a tendon with a muscle situated at the back part of
the eye. This tendon, though strong, is so fine as not to obstruct the
sight, even when it passes across the pupil, and the muscle which moves
it being situated deeply within the orbit, derives from its situation
the advantage of not only being secure from injury, but of being out of
the way, which it hardly would have been in any position that could be
assigned to it in the front of the eye, where its function really lies.
When this muscle contracts, the membrane, by means of the communicating
tendon, is instantly drawn, as it were, by a thread, over the transparent
cornea, and when the muscle ceases to act, the elasticity of the membrane
is sufficient to bring it back into its former position. (See Fig. 6.)
[Illustration: Fig. 6.--EYE OF AN OWL, SHOWING THE ARRANGEMENT OF THE
NICTITATING MEMBRANE.
Both eyelids are divided through their middle, and everted, so as to
display the Nictitating Membrane, _a_, and the passage for the tears
(_puncta lacrymalia_), _b_.]
But this is not all. In the arrangement of the muscle which, though
placed behind the eye, draws the nictitating membrane in front of
it, there is what justly deserves to be called a marvellous piece of
mechanical contrivance. The extent of contraction necessary to draw
the membrane over the whole front of the visual organ would require a
much longer muscle than could have been placed in such a situation;
in order to meet this difficulty, the tendon which draws forth the
nictitating membrane is made to pass through a loop in another muscle, as
represented in the next wood-cut (Fig. 7), where it is evident that, by
the simultaneous contraction of both these muscles, the extent of their
action when drawing the nictitating membrane over the eye is considerably
increased. Neither is this the only advantage derived from so ingenious a
contrivance; were it not for the plan adopted, the tendon of the muscle
_u_ _x_ would press upon the optic nerve, and thus materially interfere
with vision--an inconvenience that by the existing arrangement is totally
prevented. Devices like these, whereby special machinery is introduced
for special purposes, speak for themselves; we acknowledge their beauty,
and in them we recognise at once the wisdom and the goodness of the
CREATOR.
[Illustration: Fig. 7.--MUSCLES OF THE EYE-BALL AND OF THE NICTITATING
MEMBRANE.
The Muscles of the Eye-ball, _p_, _q_, _r_, _s_, are separated from their
origins, and turned aside, to show the "trochlearis" or "quadratus," _t_,
and the "pyramidalis," _u_, _x_; the latter of which passes through a
loop in the former, so as to gain a double extent of effect with a given
length of fibre.]
The SENSE OF SMELL in birds has afforded subject-matter for much
discussion, and great obscurity still exists with reference to the
extent to which they make use of their olfactory organs. It has been
generally asserted that birds of prey are gifted with an acute perception
of odours, and are thus enabled to discover their food at a distance;
but the rapidity with which vultures are known to assemble round the
carcase of an animal too recently killed to attract them by putrefactive
exhalations, has induced many observers to consider them as being
directed entirely by sight. That this latter is the preferable theory
appears to be sufficiently established by the experiments of Audubon,
which go to show that these birds possess a sense of smell very far
inferior to that conferred upon carnivorous quadrupeds, and that, so
far from guiding them to their prey from a distance, it affords them no
indication of its presence even when close at hand.
Having procured the skin of a deer, M. Audubon stuffed it full of
hay, and after the whole had become perfectly dry and hard, he placed
it in the middle of an open field, laying it down on its back in the
attitude of a dead animal. In the course of a few minutes he perceived
a vulture flying towards and alighting near it. Quite unsuspicious of
the deception, the bird immediately proceeded to attack the carcase, as
usual, in the most vulnerable points. Failing in this, he next, with much
exertion, tore open the seams with which the skin had been stitched, and
appeared earnestly intent upon getting at the flesh which he expected to
find within, and of the absence of which not one of his senses was able
to inform him. Finding that his efforts, which were long reiterated, led
to no other result than the pulling out of sundry quantities of hay, he
at length, though with evident reluctance, gave up the attempt, and took
flight in pursuit of other game.
Another experiment, the converse of the preceding, was then tried:--A
large dead hog was concealed in a narrow and winding ravine, about twenty
feet deeper than the level of the ground around it, and filled with
briars and high cane. This was done in the month of July, in a tropical
climate, where putrefaction takes place with great rapidity; yet,
although many vultures were seen sailing in all directions over the spot
where the putrid carcase was lying covered only with twigs of cane and
light underwood, none of them appeared at all to suspect its presence.
Nevertheless, notwithstanding the apparently decisive result of the above
experiments, anatomy teaches us that the olfactory apparatus in this
class of animals is largely developed, and indicates by its extent that
it is well adapted to investigate the odorous properties of the air taken
in for respiration.
The SENSE OF HEARING in birds is remarkably acute, as might be readily
inferred from the vocal capabilities conferred upon many of these
gifted songsters. Their music is certainly not less appreciated by
the performers than it is by their auditors. "Nobody can doubt,"
observes Bishop Stanley, "who sees a bird singing, clapping its little
wings, turning from side to side, and glancing its bright eyes in all
directions, as if courting attention and admiration, that it feels
delight and satisfaction. Did we require further proof, we have but
to recollect that the song-bird is most alert with the music of its
voice when its affections and interests are awakened by its mate during
the time of rearing its young." It is, indeed, principally during the
breeding-season that the singing power of birds is in full activity; and
seeing that in general it is only the male that possesses the musical
faculty, we may naturally suppose that its exercise is intended for the
solace and amusement of his mate during her confinement to her nest. The
nightingale himself becomes voiceless so soon as the appearance of his
nestlings calls him to more profitable employment.
[Illustration: Fig. 8.--EXTERNAL EAR OF A YOUNG OWL.
_a_, the Upper Part of the Head, partially denuded of feathers; _b_, the
Beak; _d_, the Eye; _c_, _e_, _f_, Marginal Fold of Skin surrounding a
cavity, the interior of which somewhat resembles the folds of the human
ear; _g_, Auditory Passage leading to _h_, the Drum of the Ear (_membrana
tympani_).]
It is, however, among the nocturnal birds that the faculty of hearing
is more specially developed. In the generality of birds there is no
provision made externally for catching or concentrating sonorous
impressions; but in the owls, the bustards, and a few others that venture
forth at night, we find a different arrangement. In the owls, more
especially, an external auditory apparatus is very conspicuous; not only
does the integument exhibit a variety of folds, the disposition of which
forcibly reminds us of the human ear, but the feathers upon the sides of
the head are so disposed as to fulfil in some degree the purposes of a
hearing trumpet. (See Fig. 8.) In such species the sense of hearing is
exquisitely developed.
In the generality of birds the SENSE OF TASTE can scarcely be said to
exist. The manner in which they obtain and swallow their food precludes
the possibility of enjoyment from this source, so that their tongue is
in many cases appropriated to some totally different use. In by far
the greater number the tongue is small, thin, and cartilaginous; the
extremity is flat, and incapable of being protruded beyond the bill. (See
Fig. 9.) There are, however, great varieties in the construction of this
organ, a few of which will require our notice.
The tongue of the parrot, although its substance is not so fleshy, has
some resemblance to that of man, and it is probable that this is one of
the circumstances enabling these birds to imitate the human voice with so
much facility.
In the family of the toucans and some others, the tongue, without being
extensible, is fully as long as the largely developed bill, and,
moreover, its sides are fringed like those of a feather. A tongue of this
description may probably be endowed with some delicacy of taste, enabling
these birds to appreciate the flavour of the fruits on which they feed.
Birds of the duck family have the largest tongues. Owing to its fleshy
appearance it more nearly resembles the human tongue than even that of
the parrot. Birds of this family discriminate their food not by sight,
but by the delicate sense of touch with which their tongue is endowed.
They thrust their bill into the mud, and from the mouthful thus obtained
select, by means of their tongue alone, whatever is fit for food,
rejecting the rest.
The smallest tongues are found in the night-jars and swallows, two groups
which at the same time are distinguished by having the largest mouths in
proportion to the size of their bodies; and in this case the design is
equally apparent. These birds feed upon living insects captured during
their rapid flight, and immediately swallowed whole; taste is out of the
question. A large tongue would only be in the way, and it is therefore
reduced to a mere rudiment.
[Illustration: Fig. 9.--THE THROAT OF A FOWL, SHOWING THE PARTS _in situ_.
_a_, the Lower Mandible; _c_, the Tongue; _h_, _m_, interior of the
Gullet; _i_, the Upper Larynx.]
In the preceding examples the length of the tongue never exceeds that
of the bill; but in the case of the woodpeckers it is protrusible to a
wonderful extent. On opening the bill of a woodpecker immediately after
it has been killed, the tongue seems of ordinary length, or indeed
rather short, and shaped somewhat like the spears used by the Caffres in
South Africa, called _assagais_, pointed at the end and furnished with
numerous barbs. (See Fig. 10.) This, however, is only the tip of a very
remarkable instrument. If the barbed portion be drawn out of the mouth, a
person unacquainted with its nature would think that he had got hold of
a very long earthworm that the bird had incautiously tried to swallow,
but which had stuck in its throat; hence a tongue of this description
is called _vermiform_. The point in its usual position reposes in the
ordinary manner between the mandibles; the rest is concealed, but is
susceptible of extension, at the pleasure of the bird, to four or five
times the length of the bill. The act of protrusion is effected by the
remarkable structure of the root of the tongue, or more properly of the
_os hyoides_, or bony apparatus whereby it is attached. The posterior
prolongations derived from the _os hyoides_ are compactly curved around
the back of the skull; and occasionally they are prolonged forwards
to such an extent as actually to reach the nostrils. By means of this
somewhat complex arrangement the woodpecker, having broken away the bark
of a tree by the powerful strokes of its bill, and thus laid open the
retreat of the insects beneath, suddenly darts out its tongue, spears
its prey, and instantly brings the transfixed insect into its mouth.
The SENSE OF TOUCH must be of very limited utility; indeed, there seems
to be no part of the body of a bird so constructed as to be capable of
tactile impressions. The wings, the representatives of hands and arms,
are obviously entirely unfit for the exercise of such a function; neither
do the legs and feet seem to be better suited to this purpose. The only
organ of touch about which there can be no doubt is the bill, yet even
this is generally covered with a hard sheath of horn. Nevertheless, in
some races the extremity of the bill is soft and largely supplied with
nerves. In snipes and wood-cocks, for example, the sensitive extremity of
the beak materially assists in procuring their food.
For the systematic arrangement of the class of birds, the conformation
of their feet has been found to afford characters of great importance to
the ornithologist, inasmuch as the organisation of these members must
obviously be in strict relation with the localities they inhabit. To
account for the distribution of the feathered tribes, and to explain the
relationships that exist between them and other animals, a great variety
of ingenious theories have been broached, all of them more or less
fanciful. The different families, sub-families, and minor groups into
which they have been divided have been again and again sorted, like a
pack of cards, frequently more in accordance with the whim of the player
than with the established rules of the game. And yet a little reflection
will show that the great principles of zoological classification are so
simple, and at the same time so immutable, that we sometimes cannot but
admire the ingenuity displayed in going wrong.
[Illustration: Fig. 10.--TONGUE OF THE WOODPECKER,
SHOWING THE MECHANISM EMPLOYED FOR ITS PROTRUSION.
_a_, harpoon-like Tip of the Tongue; _d_, _e_, _f_, _g_, _h_, Framework
of the Throat; _i_, _k_, Glands furnishing adhesive secretion.]
Few things are more manifest to the student of nature than that, in the
distribution of the animal creation, it has been ordained that every
locality shall be peopled by forms of life pre-eminently adapted for
its occupation. If, therefore, we are asked whether birds ought to be
arranged in circles or in squares, in hexagons or in pentagons, in groups
of five or in groups of seven, our simple reply would be by inquiring how
many localities could be pointed out as requiring appropriate occupants,
and to this question it is not difficult to find a satisfactory answer.
The earth, the water, and the air, throughout their broad domains, must
each of them be provided with inhabitants peculiarly constructed to
live in their diversified regions. Upon the earth, we find the level
ground, the mountain, and the glen; we find the pathless forests, and
the solitary trees and shrubs, and bushy underwood. We cast our eyes
upon the waters, and we see the world of ocean covering two-third parts
of this great globe, stretching from pole to pole, rolling its mighty
waves through every zone; we see the creeks and shallow bays that margin
it all round, and watch the waves as they approach the shore and lay
them down to sleep upon the beach. There are the rivers, too, and lakes,
and swamps and marshes which are neither land nor water, sometimes
overspread with floating vegetation, sometimes a broad expanse of ooze
and rushes far too soft to bear the weight of creatures that might try
to walk upon the treacherous surface. We look into the air, and there we
find between the earth and sky abundant room for birds of every wing.
If, therefore, with this little map of the world before us, we reply to
the question propounded above, we should be tempted to say that there
must necessarily be as many different types of organisation as there
are districts therein enumerated; and doubtless a reference to any
system of ornithology, however much the classification may be confused
by preconceived theories, will convince us that such is essentially the
foundation of any natural arrangement.
In taking, therefore, a brief survey of the principal groups, or ORDERS,
under which the feathered races have been distributed, we will begin
with those appointed to live on trees, inasmuch as these are regarded
by the author of the following pages as being entitled to the highest
rank in the class to which they belong, rivalling in intelligence, as
some of them do, the apes and monkeys of which they are in general the
inseparable companions.
Few people in this country have any adequate conception of a tropical
forest, and, consequently, are scarcely prepared to see whole races
of animals constructed specially for a residence in the umbrageous
wilderness within its pathless precincts. The great forest of the Amazon,
in all its primeval grandeur, stretches for a thousand miles from north
to south, and probably three or four hundred from east to west, and
over all this vast extent of territory, so closely are the branches
interwoven that, as we are told, a monkey might make his way passing
from tree to tree without ever coming to the ground except at those
points where the rivers hold their course through the tangled yet sublime
scenery. "In these untrodden vastnesses the trees, rising frequently
to a height of sixty or eighty feet, with stems perfectly straight and
without a branch, give support to the huge creepers that climb around
their trunks like immense serpents waiting for their prey, or sometimes
stretching obliquely from their summits like the stays of a lofty mast,
here twisting round each other till they form living cables, as if to
bind securely the patriarchs of the forest; there wreathed in tangled
festoons, and themselves covered with smaller creepers and parasitic
plants." Such is Mr. Wallace's description of the interior of the
Amazonian forest.
[Illustration: Fig. 11.--VISCERA OF SMALL BIRD (_Euphone violaceus_).
_a_, Crop; _b_, termination of the Windpipe, or inferior larynx; _c_, one
of the Vocal Muscles; _d_, lower portion of the Gullet; _e_, the Gizzard;
_g_, Lung of the right side; _h_, Liver; _i_, Alimentary Canal.]
"The forests of Rio Janeiro," says Mr. Darwin, "are ornamented with the
cabbage palm trees 110 feet high, with a stem so narrow that it might
be clasped with two hands. The woody creepers themselves are of great
thickness, some of them measuring two feet in circumference. If the eye
was turned from the world of foliage above to the ground beneath, it was
attracted by the extreme elegance of the leaves of the ferns and mimosæ
(sensitive plants). The latter in some parts covered the ground; in
walking across these thick beds, a broad track was marked by the change
of colour produced by the drooping of their sensitive leaves. It is easy
to specify the individual objects of admiration in these grand scenes,
but it is not possible to give an adequate idea of the higher feelings of
wonder, astonishment, and devotion, which fill and elevate the mind."
These are the localities amongst which species of the ARBOREAL
ORDERS find their Paradise, and hold undisturbed possession. Myriads
of climbing birds--parrots, macaws, and cockatoos--fill the whole
atmosphere with joyful screams, deafening the very monkeys with their
din; gorgeous toucans, with enormous bills and feathers dipped in flame,
and woodpeckers scarcely less gaily clad, make the woods echo, as with
axe-like beaks they chop their way in search of insect food.
The peculiar structure of the feet in the arboreal races is evidently
adapted to a life amongst the branches of trees: the outer toe can be
directed backwards like a thumb, enabling them to grasp the boughs as
with a hand.
If, leaving the trackless gloom of the forest, we approach the sylvan
scenery of the surrounding country, the "bosky woods" and isolated trees,
or the sparse undergrowth of bushy shrubs, we find innumerable forms that
have their feet contrived for _perching_ only. These INSESSORIAL races,
called also PASSERES, from their general resemblance to sparrows, live
upon insects, fruit, and grain; but those with strong beaks live more
exclusively upon grain, and those with slender beaks upon insects. The
proportional length of their wings is as variable as their habits. They
have four toes, generally so disposed that there are three in front and
one behind; sometimes all four in front. Their legs are slender, and they
hop rather than walk.
The forests and the trees, the bushes and the brakes, the thickets and
the hedgerows, being thus provided with appropriate denizens, we turn
our attention to the level ground; and here we find species as obviously
designed for a terrestrial existence as were the preceding groups for a
residence among the branches. The terrestrial or GALLINACEOUS birds live
principally upon the ground. Their body is large and heavy, and their
wings short and rounded, so as to be but ill adapted to prolonged flight.
They have three toes in front, which are united at their base by a short
fold of the skin, and their hinder toe is affixed above the level of the
rest. In many species the male is provided with formidable weapons in
the shape of _spurs_. To this order belong the turkeys, pheasants, and
barn-door fowls. Their legs are thick, strong, and muscular, their toes
short and powerful. They always prefer running to flying, and, indeed,
will rarely take to their wings, except when compelled to do so by the
urgency of the occasion.
If any doubt could be entertained as to the terrestrial character of the
gallinaceous birds, there can be none whatever as to those distinguished
by the name of CURSORES or runners. The principal characteristic of the
cursorial race consists in the undeveloped condition of their wings,
which are quite disproportioned to the size of their body. In some cases
these rudimentary wings are but imperfectly furnished with feathers, and
seem only to be used after the manner of sails, to catch the wind, and
thus assist in running. The living species form two families, of one of
which the Ostrich, and of the other the Apteryx, is the type.
Leaving the firm dry land, we next turn our attention to the marshes--the
dubious confines between land and water--and here we find the order of
WADERS, or, as they have been named on account of their long stilt-like
legs, GRALLATORES or stilt-walkers. These birds, as their name imports,
are characterised by the height of their legs, which are naked, and
thus adapted for wading to a certain depth into the water, where many
species catch their prey. A remarkable example is met with in this order
of the facility with which difficulties, apparently insurmountable, in
the adaptation of certain species to peculiar circumstances, have been
encountered and overcome. In India, the tanks and ponds of considerable
depth are more or less covered with the broad leaves of water-lilies
and other floating vegetation. In such places, which are far too deep
to be occupied by wading birds, and yet too extensive to be left
without inhabitants, we find a family provided with toes so enormously
lengthened, and moreover eked out by claws of such extraordinary length,
that the spread of their feet extends over a very large surface, thus
enabling them to walk over the floating weeds.
Another order of birds comprehends those whose feet are specially
constructed for swimming, constituting a NATATORIAL TYPE; for this
purpose they are placed far back upon the body, the legs are short and
compressed, and the toes are united by a web. Their plumage is thick and
shining, impregnated with oil, and closely packed with soft down, so as
to preserve them from all contact with the water. They are the only birds
the length of whose neck much surpasses that of their legs, thus enabling
them, while swimming at the surface, to obtain their food at the bottom.
Such are the DUCKS and SWANS, which are, moreover, further characterised
by having their bill covered with a soft skin, and furnished occasionally
at the sides with ridges and tooth-like points. The DIVERS, trusting to
their superior powers of battling with the watery element, are met with
further from the shore; while, at distances still more remote from land,
daring the utmost fury of the tempestuous ocean, walking upon the waters,
or riding upon the seas--
"Up and down, up and down,
From the base of the wave to the billow's crown,
In the midst of the flashing and feathery foam,
The Stormy Petrel finds _her_ home."
Lastly, in this our rapid survey of the distribution of the feathered
tribes, we have to speak of those whose element is the air. And here,
perhaps, the reader may feel inclined to remark that, with the exception
of the cursorial birds, such as the Ostriches and the Apteryx, all
the species we have had occasion to mention are more or less capable
of flight--that this is the special attribute of the whole class.
Nevertheless, upon a little consideration, he will find that amongst the
many races that fly well, there are some so pre-eminent in this respect
that all others quail before them. It is one thing to be able to fly, and
another to be furnished with wings so powerful that they never seem to
tire. It is one thing to be the champion of the coppice, but another to
be the tyrant of the sky!
The greatest powers of flight are of course conferred upon the rapacious
birds, whose business is to overtake and destroy their swift-flying
prey. To enable them to do this, their wings are necessarily of the most
perfect structure; and they may also be recognised by their feet, which
are strong, and armed with formidable talons. Of the swiftness of the
falcon we have spoken elsewhere; and any one who has witnessed the flight
of the eagle is not likely to have forgotten so grand a spectacle; his
movements are majestic, and as he sails above the clouds on outstretched
wings he seems to feel himself the monarch of the scene around. And
yet even the falcon and the eagle cannot, as regards their powers of
flight, be looked upon as the most highly gifted of flying birds. The
spread of wing of the frigate-birds measures ten feet from tip to tip,
and their flight is so powerful that they are everywhere to be seen in
tropical climates at immense distances from land; while the albatross
has been known to fly around a ship for weeks together, exhibiting such
indomitable strength of wing that it has been supposed to be capable of
circling round the world.
It is by no means our intention to trouble the reader with unnecessary
details concerning the anatomy of the creatures upon the history of which
he is about to enter; nevertheless, it is indispensably requisite that we
should give at least an outline of their internal organisation.
No one can have examined attentively the bony framework whereby the
body of a bird is sustained, without being forcibly impressed with the
lightness as well as the compactness of its construction. The most
wonderful economy is exhibited in the arrangement of the weighty material
of which it consists. The bones present in their interior extensive
cavities, whereby they are considerably lightened, and their walls,
although exceedingly dense and strong, are much thinner than in any other
animals. The extremities of the cylindrical bones are occupied by a light
open network of slender filaments shooting across in every direction from
wall to wall, and as these attenuated buttresses are likewise hollow,
it is easy to perceive how incomparably lightness and strength are here
conjoined.
The extent to which the skeleton is thus filled with air varies in
different birds in relation with their powers of flight. In the Swifts
and the Humming-birds every bone of the skeleton, even to the toes
and the claws, is permeated by the atmospheric fluid. In the opposite
extreme, the terrestrial Apteryx and the aquatic Penguin have not a
single bone thus excavated.
[Illustration: Fig. 12.--SKELETON OF A BIRD.
_a_, the Skull; _b_, Vertebræ of the Neck; _c_, Dorsal Region of
the Spine; _d_, Vertebræ that support the Tail; _e_, _e_, _e_,
the Sternum or Breast-bone; _f_, _f_, _f_, _f_, the Ribs; _h_,
the Scapula, or Shoulder-blade; _i_, _i_, the conjoined Clavicles
or Collar-bones, forming the Furculum, or "Merry-thought;" _k_,
the Coracoid Bones; _l_, the Humerus, or Arm-bone; _m_, _n_,
Bones of the Fore-arm; _o_, _b'_, Bones of the Wrist or Carpus;
_p_, _p_, the Metacarpal Bones and Rudimentary Thumb; _q_, _q_,
Pieces representing the Middle Finger; _r_, _s_, _s_, the Pelvis,
formed by the consolidation of the hinder Vertebræ of the Back
into one piece; _t_, the Thigh-bone; _u_, the Leg; _x_, _x_,
the Tarso-Metatarsal Bones, usually called the Tarsus; _y_, the
Hallux, or Hinder Toe; _z_, _z_, the Front Toes.
]
The skeleton of an animal formed for flight must be constructed upon
mechanical principles of a very refined character. The utmost lightness
is indispensable; nevertheless, in a framework which has to sustain the
powerful action of muscles so vigorous, strength and firmness are equally
essential. It is in combining these two opposite qualities that the human
mechanician exhibits the extent of his resources and the accuracy of his
knowledge; but let the best and most ingenious mechanic carefully examine
the skeleton of a bird, and we doubt not that in its construction he
will find all his ingenuity surpassed, and perhaps derive not a little
instruction from the survey.
In order to render the following account of the structure of a bird's
skeleton intelligible to the non-scientific reader, we have delineated
that of the Pigeon, and with this figure before us we shall have but
little difficulty in indicating those points with which it is essential
that the reader of the present volume should be intimately acquainted.
(See Fig. 12.)
In the back-bone, or vertebral column, we find three principal regions,
each of which will merit distinct notice.
The _cervical region_, or that portion belonging to the neck (Fig. 12,
_b_), is exceedingly variable in its proportionate length, and forms the
only flexible portion of the spine; it performs, indeed, the functions of
an arm, at the end of which the beak, the chief instrument of prehension,
is situated. The number of vertebræ entering into the composition of this
part of the skeleton is very variable; in the Swan there are as many as
twenty-three, in the Crane nineteen, while in the Sparrow there are only
nine. As a general rule, it may be observed that the neck of a bird is
never so short as not to be able to reach to every part of the body; in
many aquatic species it is remarkably elongated, whether they swim upon
the surface by means of webbed or natatory feet, like the Swan, or wade
into rivers and marshes, like the Crane or the Heron. Throughout the
entire class a very beautiful contrivance is observable in the S-shaped
curvature of this region, the joints of the upper vertebræ being so
disposed that they will bend forwards, while in the lower part they can
only be bent backwards, thus enabling the bird to lengthen or shorten its
neck with the utmost facility and gracefulness.
But if flexibility is thus admirably provided for in the cervical
region, in the thoracic portion of the skeleton which has to support the
framework of the wings, and sustain the efforts of the powerful muscles
connected with flight, firmness and rigidity become essential requisites,
and, accordingly, in the dorsal region, every means has been employed
to prevent those movements which in the neck are so advantageously
permitted. The vertebræ of this region (Fig. 12, _c_) are therefore so
consolidated as to be almost immovable; and, moreover, splints of bone
laid along the back materially add to its stability and strength. There
are likewise two sets of ribs, one firmly lashed to the back-bone, the
other strongly attached to the sides of the sternum; these dorsal and
sternal ribs are moreover united to each other by firm connections, and
a thorax is thus formed, possessing sufficient mobility to perform the
movements connected with respiration, but still affording a strong basis
for muscular action; nay, still further to strengthen this part of the
skeleton, from the hinder margin of each dorsal rib a broad flat plate of
bone (Fig. 12, _f_) is prolonged backwards, so as to overlap the rib next
behind, and thus bind the whole together as firmly as possible.
The sternum or breast-bone (Fig. 12, _e_) is developed in proportion to
the size of the three pectoral muscles subservient to flight, and is
prolonged beneath into a deep keel-like projection. In the cursorial
races, such as the Ostriches and the Apteryx, whose wings are not
available for flying, the keel is entirely wanting.
Whoever considers the position of the hip-joint in the skeleton of a
bird, and reflects how far it is necessarily removed behind the centre of
gravity when the bird walks with its body in a horizontal position, will
at once perceive that the hinder portion of the spinal column, having
to support the whole weight of the body under the most disadvantageous
circumstances, and at the same time to give attachment to the strong
and massive muscles that wield the thigh, must be consolidated and
strengthened in every possible manner, and that even the slight degree of
movement permitted in the region of the back would here be inadmissible.
Most of the hinder vertebræ are, therefore, solidly conjoined into a
single piece (Fig. 12, _r_, _s_), sufficiently strong and massive to bear
the great strain to which it is continually subjected, leaving only a few
of the hindmost pieces (Fig. 12, _d_) free, upon which the feathers of
the tail are supported.
The fore limb of a bird, although used for the purpose of flight, when
stripped of the feathers and quills that, as we have already seen,
form the extensive surface of the wing, will be found very much to
resemble the human arm in its general arrangement, presenting only
such modifications as are required for the performance of its peculiar
function.
The framework of the shoulder consists of three bones (Fig. 12, _h_,
_i_, _k_), named respectively the _scapula_ or _shoulder-blade_, the
_clavicle_ or _collar-bone_, and the _coracoid bone_. The scapula (_h_)
is a long and comparatively slender piece placed upon the ribs, and
embedded in the muscles, to which it gives attachment. The coracoid bone
(_k_) is the strongest piece of the shoulder; it supports the wing at
one extremity, while at the opposite it is firmly united to the sternum
by a broad and massive joint. But the most peculiarly formed part of the
shoulder is the _furculum_, or "merry-thought," as it is usually called
(_i i_), consisting of the two collar-bones united, so as to form but a
single fork-shaped apparatus, the presence of which materially enlarges
and strengthens the shoulder, without unnecessarily adding to the weight.
It is by the union of the three last-mentioned bones that a place is made
for the socket of the shoulder, with which the wing is more immediately
connected.
The skeleton of the wing presents the bone of the arm, called the
_humerus_ (Fig. 12, _l_), and the two bones of the fore-arm, named
respectively the _radius_ (_m_) and the _ulna_, or _cubit_ (_n_). The
_wrist_, or _carpus_, consists of two bones (_b' o_), and the metacarpus
(_p_) is likewise made up of two pieces; these, with two, or sometimes
three, rudimental fingers (_p' q q_), complete the framework of the wing.
The largest finger consists of two, or sometimes of three joints; a
second offers but a single joint; and the third, when present, is a mere
appendage to the carpus, representing a sort of apology for a thumb.
The bones of the leg likewise exhibit the same parts as exist in the
human skeleton, but modified. The _thigh_, or _femur_ (Fig. 12, _t_),
is a short and strong bone, to which succeeds the leg, consisting of
two bones (_u_), named the _tibia_ and the _fibula_, but the latter
is generally very imperfectly developed. That part which is commonly
considered to be the leg consists of the bones of the ankle and a part
of the foot (the tarsal and metatarsal bones) consolidated into a single
piece, called by anatomists the _tarso-metatarsal_ bone, but known to
ornithologists as the _tarsus_ (_x_). At the lower extremity of the
tarsus are three joints that support the three front toes (_z, z_), while
a fourth toe (technically called the _hallux_) (_y_), which is directed
backwards, is attached to it by the intervention of a small accessory
piece. In the gallinaceous order there exists a bony spur, considered by
some as representing a fifth toe.
In order to facilitate the description of a bird, it is usual for the
ornithologist to consider its exterior as being mapped out into sundry
_regions_ (see Fig. 13), to each of which has been assigned a definite
and appropriate name; with the names of these regions, and their precise
application, it is requisite that the reader should be intimately
acquainted.
A bird, like any other vertebrate animal, is divisible into the head,
the body, and the limbs; under one or other of which divisions all
subordinate parts may be classed.
The head consists of the _skull_ and the _bill_, and is joined to the
body by the _neck_. Commencing with the bill, we see that it is composed
of two pieces, corresponding to the jaws of quadrupeds; that which is
above is called the _upper mandible_ (Fig. 13, 1), that which represents
the under jaw is called the _lower mandible_ (2). The upper mandible
contains the _nostrils_ (3); its highest part is called the _culmen_
or _ridge_ (4), while the corresponding ridge of the lower mandible is
called the _gonys_ or _keel_ (9).
The lateral edges of the mandibles which meet when the bill is closed are
called the _margins_. In some birds the margins of the upper mandible
fold over those of the lower, while in others the edges meet; when
this is the case, the line of junction between the two is called the
_commissure_ (5).
In many birds the upper mandible is continued far back over the forehead,
and there dilated, so as to form a _casque_ or _helmet_. In rapacious
birds and parrots there is a belt of soft naked skin at the base of
the upper mandible, named the _cere_, in which the nostrils are placed,
while around the eye is a space, often denuded of feathers, called the
_ophthalmic_ region (11).
The HEAD is that part which lies immediately over the skull, extending
from the base of the beak to the commencement of the neck. The _front_
or _forehead_ (12) is that part of the head which lies close above the
nostrils; then follows the _crown_ or _summit_ (17), which occupies the
middle or centre of the head, forming that part which is usually occupied
by the crest in birds so ornamented. The _hind head_(18) commences at
the declivity of the skull; its lower portion is called the _nape_ (19).
[Illustration: Fig. 13.--ORNITHOLOGICAL REGIONS OF THE BODY OF A SMALL
BIRD.
1. Upper Mandible.
2. Lower Mandible.
3. Nostrils.
4. Ridge, or Culmen.
5. Commissure, or cutting edges of the Mandibles.
6. Apex, or point of the Beak.
7. The Chin.
8. Upper Throat.
9. Keel, or Gonys.
10. } Coloured Bands, usually called Bridles and Stripe.
11. }
12. The Forehead.
13. The Gape, or Rictus.
14. Space around the Eye.
15. Lower Throat.
16. Superciliary Region.
17. Crown, Summit, or Vertex.
18. Hind Head, or Occipital Region.
19. The Nape, or Nucha.
20. The Ear, or Ear-feathers.
21. The Throat.
22. The Breast.
23. The Neck above, or Upper Neck.
24. The Back, or Mantle.
25. Scapular Wing-covers.
26. Lower Back, or Tergum.
27. The Shoulder.
28. Body, or Lower Breast.
29. The Belly.
30. The Vent.
31. The Tail Feathers.
32. The Under Tail-covers.
33. Spurious Quills.
34. Secondary Quills, or Secondaries.
35. Primary Quills, or Primaries.
36. The Shoulder Margin.
37. Wing Covers.
38. Under-surface or Under-part of the Body.
39. The Tarsus, or Leg.
40. The Front Toes.
41. The Hinder Toe, or Hallux.
42. Upper Tail-covers.
]
On the sides of the head the following parts have received distinct
names:--The feathers that cover the ears, to save repetition, are usually
called the _ears_ (20): they are generally rather more rigid and their
webs more disconnected than the surrounding feathers. The space between
these and the corner of the mouth (usually called the _gape_)(13), is
termed the _cheek_.
The parts of the NECK are thus designated:--The back of the neck is
called the _upper neck_, or _nucha_ (23), beneath which is the _lower
neck_ or _auchenium_. The under-side of the neck is divided into three
regions; first, there is the _chin_ (7), or that small space just
beneath the lower mandible; to the chin succeeds the _upper throat_ (8),
between which and the broad part of the body is the _lower throat_ (15).
The BODY presents the following regions: first there is the _breast_
(22), which extends over the space which covers the breast-bone. To
this succeeds the _belly_ (29), which is terminated by the _vent_ or
_crissum_ (30). Immediately behind the vent are the _under-tail covers_
(32), which are frequently of a different colour from the surrounding
feathers.
On the upper aspect of the body we have the _interscapular region_,
sometimes called the _back_ (24), to which succeeds the _lower back_
(26), which terminates at the _rump_, or that part where the _upper-tail
covers_ (42) are inserted.
Last of all comes the TAIL, composed of long stiff feathers, called the
_tail-feathers_ (31), concerning which it is only necessary to observe
that the two middle tail-feathers are the _intermedial_, while those on
the sides are the _lateral_ tail-feathers.
The WING of a bird will be found to present a structure worthy of our
highest admiration. The object aimed at in the arrangement of its
different parts is evidently to obtain a very large and firm expanse of
surface, by employing the smallest possible quantity of material. For
the purposes of flight it is obviously necessary that the superficial
extent of the wings shall be sufficiently ample, not only to sustain
the weight of their possessor in the thin and yielding element in which
it flies, but, by the vigour of their stroke and the violence of their
impulse, to propel the bird with a rapidity proportioned to the occasion,
and, moreover, by the lightness of their touch and the accuracy of
their movements, to steer and steady its course through all the varied
evolutions whereby it is enabled to capture prey, or sportively display
the wonderful activity conferred upon the feathered tribes.
We have already seen, while examining the construction of the skeleton,
that the bony framework of the wing essentially resembles that of the
human arm, and that the limb when stripped of its feathers is no more
adapted for flying than our own. The needful expansion is obtained
altogether by the addition of the quill feathers, which, as explained in
a preceding page, combine in their structure all the qualities requisite
for the intended purpose, lightness, firmness, strength, elasticity, and
extent of surface: the central part of the arm or wing forms merely a
basis of support, into which the quills and other appendages to the wing
are securely implanted. It will therefore be easily understood that the
importance of the individual quills as instruments of flight will depend
very much upon the position they hold in the wing, of which they form
so considerable a portion, and, consequently, that they have received
names expressive of their relative efficiency. Those that are affixed to
the bones representing the hand (Fig. 12, _p_, _q q_), by the length of
their stroke, and the peculiarity of their arrangement, are obviously of
primary importance, both from their size and the situation they occupy,
and have consequently been named the "_primaries_," or the "_primary
quills_," (Figs. 2, _f_; 13, 35); they might be called with equal
propriety the "_hand-quills_," a term more particularly expressive of
the parts to which they are attached. Upon the relative length and other
proportions of the primary quills the shape and mechanical power of the
instrument principally depend; if the first primary be the longest, the
termination of the wing is sharp and pointed (_acuminate_), as in most
birds that are remarkable for the swiftness of their flight; whereas if
the second, third, or fourth of these quills should exceed the others in
this respect, the wing becomes more and more rounded (_obtuse_), and the
perfection of its action visibly deteriorated.
The "_Secondary Quills_," or "_Secondaries_" (Figs. 2, _c_; 13, 34),
are exclusively sustained by the bones of the fore-arm (Fig. 12, _m_,
_n_); from their situation being much nearer to the shoulder-joint than
the preceding, the extent of their sweep is more limited, and their
stroke much feebler; they are, consequently, as their name indicates, of
secondary importance in locomotion.
[Illustration: _Plate 4 Cassell's Book of Birds_
1. Tyrant Shrike (_Tyrannus intrepidus_).--2. Virginian Chordeiles
(_Chordeiles Virginianus_).--3. Cow-bird (_Icterus pecoris_).--4.
Crimson Honeysucker (_Myzantha garrula_).--5. Masked Weaver-bird
(_Ploceus larvatus_).--6. Fire-crested Wren (_Regulus pyrocephalus_).--7.
Rice-bird (_Padda oryzivora_).--8. Variegated Grakle (_Quiscalus
versicolor_).--9. White-tailed wheatear (_Saxicola leucura_).--10. The
Wittal Oriole (_Oriolus galbula_).--11. The Alpine Accentor (_Accentor
Alpinus_).--12. Nordman's Glareole (_Glareola Nordmanni_).--13. Alpine
Tit (_Parus Alpinus_).--14. Crested Tit (_Parus Cristatus_).--15. African
Parra (_Parra Africana_).--16. Piririguan Tick-eater (_Crotophaga
Piririgua_).--17. Ptarmigan (_Lagopus Scoticus_).--18. Scapulated Crow
(_Corvus Scapulatus_).--19. The Kestrel (_Tinnunculus Cenchris_).--20.
The Senegal Thick-knee (_Oedicnemus Senegalensis_).--21. Rock Kestrel
(_Tinnunculus rupicolus_).--22. Corythus (_Corythus enucleator_).--23.
The Red-legged Stilt-Walker (_Himantopus rufipes_).--24. The Stone Thrush
(_Turdus saxatilis_).--25. The Silk-tail (_Bombycilla garrula_).--26.
Long-tailed Tit (_Parus biarmicus_).--27. The Wall-creeper (_Tichodroma
muraria_).--28. The Troopial (_Agelaius phœniceus_).--29. The
Yellow Bunting (_Emberiza Cia_).--30. The Red-eyed Coccyzus (_Coccyzus
erythropthalmus_).--31. The Cirl-Bunting (_Emberiza cirlus_).]
The _Spurious_, or _Bastard Quills_ (Figs. 2, _e_; 13, 33), are attached
to the rudimental bone that represents the thumb (Figs. 2, _g_; 12,
_p_); their size is diminutive, and their use in flight comparatively
unimportant.
The _Wing Covers_ or _Coverts_ (Fig. 13, 37) are small feathers arranged
in several rows, which overlap and strengthen the bases of the quills;
they are often variously coloured, and thus afford important features
whereby different species may be distinguished. Besides the above, there
are certain conventional terms employed by the ornithologist that will
require enumeration. The arm-part of the wing in the living bird is
generally known as the _shoulder_ (27); the elbow-joint is the _flexum_;
while that part of the fore-arm which corresponds to the edge of the wing
is denominated the _shoulder-margin_ (6).
The names appropriated to the different parts of the hinder-limb have
been already sufficiently indicated when describing the composition of
the skeleton.
There are many birds which have stripes of variously coloured feathers
situated above, before, and behind the eye; while others sometimes occur
at the base of the lower mandible. To all these distinct names have
been appropriated. A _superciliary_ stripe is situated _above_ the eye,
occupying a position analogous to that of the human eyebrow. An ordinary
eye-stripe is either _anterior_, _posterior_, or _entire_. It is called
_anterior_ when it only occupies the space between the eye and the bill;
_posterior_ when it commences behind the eye, and advances towards or
unites with the ear-feathers; and _entire_ when it is both posterior
and anterior. A _maxillary_ stripe commences at the base of the under
mandible, and descends on the sides of the neck.
[Illustration: Fig. 14.--CHICKEN IN THE EGG, NEARLY ARRIVED AT MATURITY,
Showing the little Hammer or "Bill-scale" on the end of its beak,
wherewith it is enabled to break through the egg-shell.]
Such is the by no means very long list of names of parts used by the
ornithologist in his description, and which in the course of the present
volume will necessarily be of very frequent occurrence.
The oil with which birds preen their feathers, and the glands that supply
it, constitute a remarkable provision peculiar to the feathered creation.
Embedded among the feathers at the root of the tail, there is on each
side a small nipple, yielding upon pressure a butter-like substance,
which the bird extracts by squeezing the orifice with its bill. By means
of the oil, or rather ointment, thus procured, it dresses its feathers,
either for the purpose of increasing their brilliancy, or, as in the case
of the swimming birds, to make them impenetrable to wet.
The pairing of birds is a feature in their history which draws a broad
line of distinction between the feathered tribes and the generality of
quadrupeds. Among mammiferous quadrupeds the young derive their nutriment
during the earlier period of their existence entirely from the maternal
breast, the male parent contributing nothing towards its support; but in
the winged races the callow brood derive their supply of food from the
industry of both parents, whose united exertions are not more than is
requisite to procure the needful supply. In this circumstance we may see
a reason for the faithful love of the feathered mate as contrasted with
the vagrant disposition of the quadruped. The parental fondness of birds
towards their young has escaped no observer; no historian of nature is
silent upon this subject. "How well they caress them," says Derham, "with
their affectionate notes, lull and quiet them with their voice, put food
into their mouths, cherish and keep them warm, teach them to peck and
eat, and gather food for themselves, and, in a word, perform the part of
so many nurses deputed by the Sovereign Lord and preserver of the world
to help such young and shiftless creatures."
It would lead us far beyond the limits of our space were we to do more
than indicate the close relationship that exists between the exalted
temperature and warm clothing of the feathered creation and the wonderful
instinct which urges them to build nests for the reception of their
eggs, or the still more remarkable blind perseverance with which they
devote themselves to the task of incubation. "There is nothing," says
Paley, "either in the aspect or in the internal composition of an egg
which could lead even the most daring imagination to conjecture that it
was hereafter to turn out from its shell a perfect living bird. From the
contents of an egg would any one expect the production of a feathered
goldfinch? To suppose the female bird to act in this process from a
sagacity and reason of her own is to suppose her to arrive at conclusions
there are no premises to justify." And yet HE who made the egg not
only ordained that such should be the result of the simple process of
incubation; but, as though to confound scepticism, by giving, as it were,
the last touch to HIS inscrutable work, provided the young bird with the
means of escaping from incarceration, by attaching to the end of its beak
a little hammer, called the "bill-scale," the only use of which is to
crack the egg-shell, and allow the little prisoner to come forth. (See
Fig. 14.)
With these few prefatory remarks, we leave our author in the reader's
hands, at the same time promising that he will find in the succeeding
pages a rich store of valuable information.
[Illustration: Fig. 15.--A YOUNG BLACKBIRD SHORTLY AFTER ITS ESCAPE FROM
THE EGG, SHOWING THE ARRANGEMENT AND CONDITION OF THE FEATHERS.]