BIRDS IN FLIGHT
[Illustration: _Kingfisher and Young_]
BIRDS IN FLIGHT
BY
W. P. PYCRAFT
Zoological Department, British Museum (Natural History).
Fellow of the Zoological Society of London.
Hon. Member of the American Ornithologists' Union.
Associate of the Linnean Society.
Member of the Marine Biological Association of the United Kingdom.
Member of the Royal Anthropological Institute.
Author of "A History of Birds," "The Infancy of Animals," "The
Courtship of Animals," "The Sea-shore," Etc., Etc., Etc.
_Illustrated by_
ROLAND GREEN, F.Z.S.
LONDON
GAY & HANCOCK LIMITED
34 HENRIETTA STREET, COVENT GARDEN, W.C.2.
1922
_All Rights Reserved._
CONTENTS.
CHAPTER PAGE
I. Concerning Wings 1
What a wing is--The quill feathers and their function--The
skeleton of the wing--The muscles of the wing--The
great air-chambers of the body--The Bat's wing--The
wing of flying Dragons--The wings of Dragon-flies
and beetles.
II. The First Bird 15
The ancestors of birds--The first known bird and its
many remarkable features--The gradual evolution of the
birds of to-day.
III. The Sizes and Shapes of Wings and
their relation to Flight 21
The evasiveness of flight--The size of the wing in relation
to that of the body--Noisy flight--"Muffled" flight--The
swoop of the sparrow-hawk--The "flighting" of
ducks--The autumn gatherings of starlings and swallows--"Soaring"
flights of storks and vultures--The wonderful
"sailing" feats of the albatross--The "soaring" of the
skylark--The "plunging" flight of the gannet, tern, and
kingfisher.
IV. Modes of Flight 35
The movements of the wing in flight--Marey's
experiments--Stopping and turning
movements--Alighting--"Taking off"--Hovering--The use of the
tail in flight--The carriage of the neck in flight--And of the
legs--The flight of petrels--The speed of flight--The height
at which birds fly--Flight with burdens--Experiments on the
sizes of the wing in relation to flight--Flight in "troops."
V. Courtship Flights 53
The wing-play of black-game and grouse--The "musical
ride" of the snipe--The "roding" of the woodcock--The
musical flights of redshank and curlew--The "tumbling"
of the lapwing--The raven's somersaults--The
courting flight of the wood pigeon--The mannikin's
"castanets"--Wings as lures--The strange pose of the
sun-bittern--The "wooing" of the chaffinch and the
grasshopper-warbler--Darwin and wing-displays--The
wonderful wings of the argus-pheasant.
VI. How to tell Birds on the Wing 71
The small perching-birds and the difficulty of distinguishing
them--The wagtails--The finches--The buntings--The
redstart-wheatear, Stonechat--The thrushes--The
warblers--The tit-mice--The nuthatch, and tree-creeper--The
spotted flycatcher--The red-backed shrike--Swallows,
martins, and swifts--The night-jar--Owls--Woodpeckers.
VII. How to tell Birds on the Wing 97
(_continued_)
Falcons--Golden eagle--Harriers and sparrow-hawk--The
heron--The cormorant, shag, and gannet--The petrels--Guillemots,
razor-bills, and puffins--The ducks--The
great crested grebe and dabchick--The pigeons--The
"plover tribe"--The gulls and terns--The game birds.
VIII. The Wings of Nestling Birds 117
The wing of the unhatched bird--Of the coots and water-hen--The
hoatzin's wings--The wing of Archæopteryx--Moulting--The
nestling game-birds and ducks--Teaching
the young to fly.
IX. Flightless Birds 127
The steamer duck--The owl parrot--The flightless grebe
of Titicaca--The dodo and solitaire--The ostrich tribe--The
penguin's wings.
ILLUSTRATIONS
Coloured Plates
Kingfisher and Young _Frontispiece_
Jays _Facing Page_ 6
Pheasants " " 22
Brown Owl " " 30
Wild Duck " " 38
Woodcock carrying Young " " 54
Herons " " 64
Chaffinch and Young " " 76
Gold-crested Wrens " " 86
Great Spotted Woodpeckers " " 92
Some Types of Wings and Tails " " 102
Grouse " " 118
Black and White Plates
Swans, Heron, Geese _Facing Page_ 4
Black-game " " 26
Ducks " " 42
Lapwings " " 58
Some Common Birds _Facing Page_ 72
Some Types of Birds in Flight " " 80
Birds of Prey " " 106
Flightless Birds " " 130
Line Illustrations
Wings _Page_ 13
Archæopteryx and Pterodactyles " 19
Bat, Beetle, Dragon Fly, etc. " 33
Peregrine chasing Duck " 51
Sunbittern Displaying " 69
Drumming Snipe " 95
Buzzard Soaring " 115
Gulls " 125
Vultures " 133
Preface.
There are hosts of people who have a genuine
love of our native birds without yearning to possess their skins, or
desiring to acquire the reputation of being "Ornithologists." They
would call them all by name if they could, but seek, alas! in vain, for
some book wherein they will find some magic phrase which will enable
them to identify every bird they meet by the wayside.
Most of our native birds have learnt that "discretion is the better
part of valour," when in the neighbourhood of Man. Hence one gets but
too often no more than a fleeting glance at their retreating forms,
which, from frequent encounters, have become familiar, yet they leave
no more than a vague image in the memory. "What bird _was_ that? I have
often seen it but have never succeeded in taking it unawares." This is
a question, and its comment, often put to me.
Those who are in this quandary, and they are many, are always hoping to
find some book which will enable them to correctly name the retreating
forms. That book will never be written. In the following pages an
attempt is made to aid such enquirers, and at the same time the
difficulties of the task are pointed out.
It is hoped, however, that this attempt will find a welcome among
those for whom it is made. If it helps them to understand something,
at least, of the absorbing and fascinating problems which the study of
flight in the animal kingdom presents, it will at least have served
some useful purpose.
The pursuit of the flying bird will inevitably stimulate a desire
to know more about the bewildering changes of plumage presented at
different seasons of the year, as well as by the striking differences
which often distinguish the two sexes, and the immature birds. The
endeavour to satisfy this desire will open up a new world. Those
who would pass to this knowledge should possess themselves of the
"Practical Handbook of British Birds." Though most severely practical,
and designed for the serious student alone, even the beginner will find
interest in the description of these several plumages, and much else
beside that it is essential to know.
Now that the study of flight is so much to the fore, some may turn to
these pages in the hope of gaining useful information on the theme of
mechanical flight. Some help they may find. But it was not for this
that they were written. The flight of an aeroplane and the flight of a
bird have little in common--at present; though something may be learned
by the study of gliding flight and soaring, which of course have their
place in this book. But anatomical details and mechanical formulæ,
necessary to the serious student of flight, would have been entirely
out of place here, and they have been omitted.
My task has been by no means easy. But it has been enormously helped
by the extremely skilful and beautiful work of the artist, Mr. Roland
Green. Where birds are concerned, few artists in the past, and very few
in the present, have shown any ability to combine accuracy in drawing
with ingenuity of composition and faithfulness in colouring. Mr. Green
has shown this rare combination; his coloured plates and line-drawings
speak for themselves.
W. P. PYCRAFT.
_London_,
_September, 1922_
CHAPTER I.
Concerning Wings.
"Divinity within them breeding wings
wherewith to scorn the earth."--_Milton._
What a wing is--The quill feathers and their function--The skeleton
of the wing--The muscles of the wing--The great air-chambers of
the body--The Bat's wing--The wing of flying Dragons--The wings of
Dragon-flies and beetles.
The flight of birds has always aroused man's
envy and stirred his imagination. David longed for the wings of a dove:
the writer of the Book of Proverbs tells us that "the way of an eagle"
surpasses his understanding. Icarus, spurred on by dire necessity,
actually, we are told, contrived to fly--but his maiden effort ended in
disaster! To-day we have, in a sense, succeeded where he failed. But
only because we have given up the idea of flight by personal effort,
and make our aerial journeys in a flying machine.
That we owe much of our success to a study of the flight of birds is
common knowledge, but the machine which has evolved as a consequence
of this study pursues its way through the air after a very different
fashion from that of the birds, for its vast body is thrust, or drawn,
through the air by means of a propeller, driven at incredible speed,
its immobile wings sustaining the weight. The wings of the bird, on the
other hand, not only lift the body from the earth, but they sustain it
in the air by their marvellously complex movements. And this is true,
in varying degrees of bird, and bat, and butterfly: of dragon-fly and
beetle.
Even they who must perforce dwell in crowded cities see daily the
miracle of flight performed. For even here sparrows and pigeons, at
least, are everywhere, and it is just because this is so, just because
they have become so "common-place," that their very presence escapes
notice. Yet the wonder of their movements in the air might become a
never-ending source of delight if only we went about our business with
open eyes and minds alert.
Watch the wary sparrow spring from the ground and dart across the road,
or up to the nearest house-top. How is it done with such incredible
speed and accuracy?
To understand even the broad principles of flight, it is necessary to
realize, at the very beginning, that the wing, in the case of the bird,
or the bat, is a specially modified fore-leg. So also is the human arm
and hand. But its transformation has not been so drastic as that of the
bird, or the bat. Wherein the hand has been, as it were, completely
re-modelled to fulfil the peculiar and complex functions demanded of
it.
How should one describe the wing of a bird, as one sees it in flight?
The Dictionary, obscure and inaccurate as Dictionaries usually are,
defines a wing as "the organ of a bird, or other animal, or insect,
by which it flies--any side-piece." Might not the impression one
gathers of a wing, during flight, be defined as of a lateral extension
of the body, presenting a relatively large surface, but having no
appreciable thickness? That surface, examined in a dead bird, is seen
to be formed, for the most part, of a series of parallel, tapering,
elastic rods, fringed with an innumerable series of smaller, similar,
but much shorter rods, closely packed, and linked together by some
invisible means to form an elastic web? These we call the "quill,"
or "flight-feathers." The rest of the wing, and the body itself, is
clothed with precisely similar structures, differing only in their
smaller size. We call them "feathers" commonly, without realizing that
they are the "Hall-mark" of the bird, for no other creature has ever
been similarly clothed.
These quill-feathers play such a tremendously important part in flight
that their arrangement, and relation to the underlying skeleton must
be carefully examined by all who would understand the flight of birds.
To begin with, then, note that they are so arranged as to overlap one
another, the free edges of the quills facing the outer edge of the
wing. Only by this arrangement would flight be possible, for on the
upstroke of the wing through the air the quills act like the shutters
of the sails of a windmill, allowing the wind to pass between them and
so relieving pressure on the uplifting wing-stroke. On the down-stroke,
the opposite effect is produced. The full force of the stroke is
conserved, because, owing to the overlap, the several feathers are now
pressed closely together to form an impervious sheet.
How are they fixed to the skeleton? To see this all the smaller
feathers and the muscles, or "flesh" of the wing must be removed.
It will then be found that the flight-feathers are divisible into
two series. One, widely spaced, runs along the upper surface of the
fore-arm: the other, closely packed, along what answers to the back
of the hand. In effect this is but a single rod of bone, but it is
composed of three elements, answering to three of the digits of the
human hand--the thumb and the first and second fingers. But they are
scarcely recognizable as such, for the thumb is reduced to a mere
stump, while the two fingers have become welded together. The third
finger, indeed, has become reduced to the palm-bone, and a short stump
answering to the first finger joint. To this frame-work, which can be
folded up into the shape of a Z when the bird is at rest, the quills
are fixed by their base by means of slender, but very strong elastic
tendons. In birds which have a long upper arm bone, like the Albatross,
Gull, or Heron, there is a third series of long, almost "quill-like"
feathers running from the elbow to the body, thus closing up what would
otherwise be a gap between the wing surface and the body, rendering
flight impossible.
[Illustration:
Swans.
Heron.
Geese.
]
The most important muscles of the wing are those which have to provide
the power for the down-stroke of the wing. And these are the "pectoral"
or "breast-muscles"--which form such dainty meat in a roast fowl.
Owing to their great bulk the breast-bone itself would be insufficient
to afford them attachment. This is furnished by the development of a
deep, median keel, so that the breast-bone of a bird, such as a pigeon,
bears a fanciful resemblance, when seen in profile, to the hull of a
ship--unusually shallow--with a very deep keel. The front end of the
breast-bone supports two slender rods of bone, and these in their turn
support the long, sword-like blade-bone, and the "merry-thought."
The general appearance of this frame-work for the support of the wing
and its muscles can be seen in the adjoining illustrations. But it
must be remembered that in their relative sizes and disposition these
various parts present a very considerable range of differences. That
these differences are correllated with different forms of flight goes
without saying, but, be it noted, no one, as yet, has attempted to
discover in what way they are related. Some of the readers of this book
may, perhaps, be tempted to try and solve the problems which these
differences present. To begin with, a collection of breast bones of
different species of birds with their attached shoulder-girdles should
be made, and these should be studied together with careful observations
of the flight of the living bird. So far only a few comparisons of this
kind have been made.
It must not be supposed that the whole secret of flight in birds
is concentrated in the skeleton of the breast-bone and its
shoulder-girdle, and the muscles attached thereto. But those who would
investigate the modifications of the rest of the body which have taken
place in harmony with the requirements of flight, must turn to more
learned treatises. There is, however, one point which demands notice
here. And this is the popular belief that birds have the power of
materially reducing their weight when on the wing by drawing air into
their lungs, and storing it in large air-chambers enclosed within the
body. These chambers are indeed concerned with the needs of flight. But
the precise part they play is yet to be discovered. They certainly have
no effect of rendering the body lighter. So far as our knowledge goes
it would seem that they act as regulators of the temperature and as
reservoirs of breathing air, during the strenuous efforts of flight.
[Illustration: _Jays_]
It is a mistake to suppose that it is unnecessary to consider other
kinds of flight when studying that of birds. Even those who are not
interested in the abstruse problems of the mechanism of bird's flight,
will find that comparisons made between birds, bats, butterflies and
beetles when on the wing, are immensely interesting, and help to bring
out the peculiarities of each.
During the twilight hours of a still summer evening one may compare,
with advantage, the rushing swoop of the screaming swift, borne with
lightning speed upon long, ribbon-like pinions, with the curiously
erratic flight of the woolly bat with beaded eyes, who has ventured
abroad for his evening meal. One cannot but feel astonishment at the
marvellous dexterity with which he twists and turns, now shooting up
into the sky, now darting downward. What bird can beat him, or even
match him, in the art of doubling back on his tracks? And one can put
his skill at lightning turns to the test if one attempts to catch him
in a butterfly net. Often indeed have I attempted this feat, but never
yet with success.
In the glare of noon-day this aerial athlete may perhaps be found in a
deep slumber, hanging head downwards behind the shutters of a cottage
window, or in some crevice of a barn-roof. Gently seize him and as
gently stretch out his wing. The moment one opens it one sees that it
is constructed upon a totally different plan from that of a bird. In
the first place a thin membrane, or fold of skin is seen to take the
place of the series of quill-feathers found in the wing of the bird. In
the second it will be found that this membrane is stretched between
a series of long and very slender bony rods. These are excessively
attenuated fingers. And if the hinder border of the wing-membrane be
traced inwards it will be found to be attached to the hind limb. In
some species it will be found that this membrane passes backwards
beyond the leg to attach itself to the tail. Here, then, is a wing
as efficient for its purpose as that of a bird, but constructed on a
totally different plan.
Ages ago, before even the birds or the beasts had appeared on the
earth, the winged dragons, which the Men of Science call Pterodactyles,
held the proud position of being, not only the first, but the only
creatures blessed with a backbone that could fly. Their wings
resembled those of the bats, but differed in this, that instead of the
wing-membrane being stretched between all the fingers, leaving only
the thumb free, it was attached only to the fifth finger, leaving the
remaining fingers free, and these were reduced to mere vestiges. As
with the birds, the breast-bone was very broad and was furnished with a
keel, while in the bats it takes the form of a jointed rod, down which
no more than a slight keel is ever developed.
But millions of years before the Flying-dragons, birds, and bats came
into being, the stupendous problem of flight had been solved. Far away
in the distant Devonian Epoch, when the distribution of land and water
over the earth's surface was totally different from that of to-day,
dragon-flies and caddis-flies disported themselves in the summer sun,
amid landscapes that would seem strange to our eyes. For there were no
trees and flowering plants, such as we know.
* * * * *
The dragon-flies of that remote epoch were very like those of to-day,
whose dancing flights and graceful, swooping movements are such a
delight to watch by reed-fringed pools, or river-banks, during the
sweltering days of summer. This flight is very different from that of
a bird, though it would be hard to say precisely in what it differs.
But we have no such difficulty in regard to the broad outlines of the
mechanism of such flight. To begin with there are two pairs of wings,
and these appear to be fashioned out of some curiously gauze-like
material, a sort of mesh-work tissue, often strikingly coloured. And
they are obviously driven after a very different fashion from those
of the bird. For in the bird they are moved by quivering muscles,
attached to a bony, internal skeleton. In the dragon-fly--as with all
insects--the hard skeleton, composed of a material known as "chitin,"
forms the outside of the body and encloses the muscles. Finally, for we
may not dwell very long over this aspect of flight, it is clear that
the wings cannot have been derived from modified fore-legs, like those
of the bat, or the bird. Rather, it would seem, they have developed out
of plate-like breathing organs.
The restful twilight hours of summer tempt not only bats from their
hiding places, but a host of other winged creatures which are rarely
to be seen, or heard, during the glare of noon. Among these is the
lumbering dor-beetle, who, with lazy drone steers clear of solid
objects only with difficulty. Many, indeed, are his failures. He and
his kin are no match for bats and owls, who find them juicy morsels! On
the next opportunity catch one and examine him. His wings are curiously
interesting. There are the usual two pairs: but the fore-wings have
been changed to serve as covers for the hind-wings. During flight they
are spread outwards, and indirectly, no doubt, assist flight. But the
hind-wings are the real propellers. And it will be noticed that when
not in use they can be folded up in a perfectly wonderful manner, so as
to lie completely underneath the fore-wings, or "elytra," so that when
the creature is crawling it appears to be wingless.
Now compare these with the transparent wings of the bee, or the
gorgeously scale-covered wings of the butterfly. It is well worth
while. If this examination be done very carefully, and with the aid
of a magnifying glass, it will be found that the fore and hind wings
are yoked together in the wing of the bee, by a delicate mechanism
of hooks. In the moths, but not in the butterflies, a bristle, or
sometimes two or three bristles, serve the same purpose. Further, in
the case of the bee it will be found that the fore-wing, when at rest,
is folded longitudinally back upon itself.
Finally, turn to the flies. Herein it will be seen that there is but
a single pair of wings, the hind pair having become reduced to mere
stumps, known as "balancers."
Much, very much more, might have been said of these wings: but our
conversation is of birds. We cannot, however, properly appreciate
either the essential characters of their wings, or their flight,
without some such standards of comparison as is afforded by the wings
of other creatures.
[Illustration:
A Primaries. B Secondaries. C Tectrices. D Bastard Wing.
The upper figure shows the under side of wing with the coverts removed
to show attachment of flight feathers to skeleton.
The lower figure shows the quill or flight feathers and the coverts in
their natural condition.]