William Beebe.

The bird, its form and function online

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due to environment (using that word in its widest sense)
cover a vastly greater field and one as yet comparatively
unexplored.

Advancement of actual knowledge of any subject in



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290 The Bird

science depends upon two things: first, the accumula-
tion of facts; and secondly, a philosophical spirit capable
of generalizing and bringing order out of the chaos of



Fig. 229.— Breast of Scaled Partridge.



Fig. 230. — Carp, a fish with distinctly marked scales. (Keller, photographei.)

these myriad observations. A knowledge of museum
facts is of but slight use in such a subject as the one under
consideration, which requires more adequate knowledge



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The Body of a Bird 291

than we now possess of the Hfe-habits and the psychology
of birds. This is especially true of the great number of
cases which we can explain only by calling them orna-
mental and decorative. Hence we find one ornithologist



Fig. 231. — White-throated Sparrows. The Hght-coloured bird is in normal plu-
mage; the dark bird was subjected to moisture-laden air through two moults.

explaining a certain colour as due to one cause, while
another scientist gives an entirely different interpretation
of the same fact.

From personal observation among the birds of the



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292 The Bird

New York Zoological Park, I have had opportunity to
record many cases of the effect of food upon colour. An
experiment very commonly known is that of feeding
canaries on red pepper, thus causing their plumage, after




Fig. 232. — Variation due to climate, etc., in races of North American Song Sparrows.
(From a photograph provided by the American Museum of Natural History.)

successive moults, to become of an intense orange colour.
This is the more remarkable since the actual red pigment,
or capsicin, of red pepper is not the direct cause of the
canaries' changed hue, but a fatty substance known as
triolein, which is a constituent of the pepper.



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The Body of a Bird



293



It is generally thought that the fact that, in captivity,
Purple Finches and orioles frequently moult into yellow-
ish hues, instead of their rightful tints, is due to some
change in food. Indeed in many species the bright colours
are wholly lacking after a year or two in captivity. But
I have transferred a male Purple Finch, which had for
several years moulted yellow, from a dark cage to one
which was exposed to
bright sunlight, and in
one moult the bird as-
sumed his original and
normal colour.

A more probable ex-
ample of the effect of
food upon colour is seen
in our American Flamin-
goes. In captivity these
birds fade out moult by
moult, until they become
almost white, like the
European species. By
mixing with their food
a quantity of some
strong but harmless dye,
I have had them either retain their original colour for
years, or at least the fading process has been appreciably
lessened.

The effect of climate upon colour is even more readily
proved, and may be noticed in wild birds as well as in
those in captivity. In regions which have a very dry



Fig. 233. — Effect of environment on Bob-
white, shown by specimens from Min-
nesota, Florida, and Cuba. (From a

3h provided by the American

of Natural History.)



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294



The Bird



climate, the birds, and in fact all of the animals, are of
a much lighter hue than those living in an atmosphere
of great humidity, where moisture does not readily evapo-



FiG. 234. — Male Scarlet Tanagers, showing moult from the scarlet summer dress,
(a), through the parti— coloured garb (b), into the green winter plumage (c).

rate. In such a place birds tend to be very dark-coloured.
In the case of captive birds, I have seen White-throated
Sparrows and Wood Thrushes become almost like black-



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The Body of a Bird 295

birds in colour when confined in a bird-house where the air
was constantly moist. Correlated with the effect upon
colour is often a difference in size, and in many instances
among birds the more northerly individuals are larger,
those inhabiting warmer regions being less in stature.

Among wild birds, the Quail, or Bob-white, shows an
almost unbroken series from the northern, light-coloured
variety, ten inches in length, to the Cuban bird, very



Fig. 235. — Siberian Black Lark, male bird in the spring.

much darker in shade and measuring only eight inches
from beak to tip of tail. The race of Bob-whites seems
very susceptible to climatic influence; as in Mexico there
are nearly a dozen different geographical races, each in-
habiting a distinct portion of the country. Many other
wide-spread groups of birds, such as the Song Sparrows,
vary in a similar manner. It is strange what a marked
effect this greater or less amount of moisture has upon
birds, even in very limited districts. A South Ameri-
can pipit, the individuals of which spend their lives on
very circumscribed plots of earth, exhibits two colour



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^9^ The Bird

forms entirely different, and thought to be due solely
to the amount of moisture in the ground on which it lives.
Very dark-coloured and very pale individuals live within
a few hundred yards of each other, in dry and swampy
situations respectively, each, it is said, keeping entirely
to its own little beat.

We are all familiar with the changes of colour due to



Fig. 236. — Night hawk i^erchmg lengthwise on a fallen branch.

age, as, for instance, in the young Rose-breasted Gros-
beaks, which are very different from the male parent, and
the young Bald Eagles, which lack the white colour of the
feathers of head and tail. Certain wild pigeons show
marked differences in colour patterns between the young
birds and the adults, and ver}^ good evidence of the gradual
evolution which must have preceded these changes is



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The Body of a Bird 297

to be found by plucking out a few of the feathers of the
young bird. Those which replace the ones pulled out
will show intermediate stages, which have long since been
dropped from the sequence of patterns, as observed in
the regular moults of the birds.

Another important phenomenon is the seasonal moult,
which was spoken of in the chapter treating of feathers-
In the fall of the year the brilliant Scarlet Tanager assumes
the olive-green dress of the female, and the Indigo Bunt-
ing and the Bobolink likewise don the dull garb of their
mates.

There is another very interesting cause of change in
colour, namely, the wearing off of the brittle tips of the
feather-vane. An excellent example of this is seen in the
Snowflakes, which come south in the depth of severe
winters, flying in small flocks about our fields, like an
animated flurry of the actual crystals. When we see
the birds at this time they are brownish and brownish
white. In the spring, in their northern home, they change
to a clear-cut black and white, not by shedding the entire
plumage, but merely by the breaking off of the brown
feather-tips. By a similar process the Bobolink changes
from the buffy female dress to his rich black-and-white
spring suit, and, as we saw in Chapter II, Fig. 35, the
English Sparrow gains his cravat of jet.

Another excellent example is found in the Black Larks
of Siberia, the males of which, in winter, are of an almost
uniform sandy colour, like a Skylark, but by the wearing
off of the buff tips of the feathers, the birds become jet-black
in the summer — a most remarkable and radical change.



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The Body of a Bird 299

The relation of a bird's colours to its haunts and its
habits of life is a subject of intense interest. This is,
of course, not in the same category as the subjects of the
foregoing paragraphs, but indeed includes them all. The
most common class of colours is known as protective.
These are such that the bird resembles its environment
or surroundings and is thus given a better chance of escap-
ing the observation of its enemies. It is evident that,
in a study of this nature, observation of the bird in its
natural haunts is of far greater value than any other
method.

We find that the majority of sparrows, sandpipers,
and quail are gray or brown, like the grasses, sedges, and
leaves among which they Uve; while the birds which
spend their lives higher up among the branches of trees
are greenish, or at least more brightly coloured.

Many birds which are protectively coloured are dark
above and white or whitish beneath. The significance
of this pattern of coloration has been beautifully demon-
strated by an American artist, Mr. Abbott Thayer. His
experiment, which is as follows, may be repeated by any
one: Take two wooden decoy ducks, and place them
against a sand-bank. Colour one the exact tint of the
sand, or even coat it with that substance. Repeat this
with the upper parts of the second decoy, makmg its
back darker than the surroundmg sand, but grade the
under part of this one to pure white below. At a little
distance away, decoy number one will still be distinctly
seen; while number two will absolutely disappear, merg-
ing perfectly mto its background. The reason for this is



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300 The Bird

that the conspicuous white of the under surface of the
second bird is, when normally lighted up by the sun,
neutralized by the shadow of the bird, and the darker
upper parts are softened and toned down by the strong
direct light; while if the entire bird be unshaded, although



FiQ. 238. — Sooty Tern on her nest.

coloured like the environment, the dark shadow beneath
will reveal it clearly.

Whether or not birds really appreciate the value of
the protective colour of their plumage, it is certain that
a quail or ptarmigan will remain crouching on a brown
bit of turf, until all hope of evading danger is gone; while
birds which are very evidently not protectively coloured
are invariably more wary and difficult of approach. When



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Fig. 239. — Seven young Flickers clinging to a tree. (R. H. Beebe, photographer.)

301



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302



The Bird



a ptarmigan, while yet in the brown garb of summer,
is exposed against a hillside of snow, it becomes very
wary.

It is interesting, in this connection, to observe how a
Nighthawk carries out its colour resemblance to a knot
or a rough piece of bark, by perchiyg, not crosswise, but
lengthwise, along a branch or fallen tree-trunk.

A volume might easily be written of the various ways
in which protective coloration works out among birds,
but there is so great a difference of opimon, and indeed
so many exceptions to every theory which may be ad-
vanced, that it is better, for the most part, to go to Nature
without a priori theories, and putting ourselves as nearly
as possible in the position of the creatures themselves,
to hope for better ability to see with their eyes. And
it is right along this line that we most need fresh data
and experiments, namely, the actual ability of birds
and insects to distinguish shades, colours, forms, and
motion, — ^whether efficient in certain ways or not. We
know that many men cannot distinguish a scarlet ball
lying upon green grass; that is, they are partly colour-
blind. If this were the case with certain hawks, a male
Scarlet Tanager would be forever safe from them among
the green foliage.

An important fact, which for years had been appar-
ent to me, but unexpressed until Mr. Abbott Thayer put it
into words, is that colours which we would ordinarily term
conspicuous are often exactly the opposite when found in the
plumage of a bird. Writing of the Motmot in my volume
''Two Bird-lovers in Mexico,'' I say: ''I have often



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The Body of a Bird 303

wondered, when I saw mounted specimens in museums,
with what special immunity from danger these birds
were blessed, their beautiful colouring would seem to be
such a startling advertisement of the bird's whereabouts.
But in reality the very diversity in hue is their protec-
tion, and they merge per-
fectly into their environ-
ment of green foliage and
bright sunlight/'

Indeed absolute uniform-
ity of coloration instantly
reveals the outline of the
bird entire, and renders it
very conspicuous. Birds
which have but few ene-
mies are often thus mono-
crome in hue. But look
at the photographs and

see how a broken COlora- Fig. 240.-Brown Creeper circling up the

tion baffles the eye. If trunk of a spruce.

the Sooty Tern, Fig. 238, were totally black, it would
be conspicuous even against a patch of dark-coloured
mottled shingle. But the transverse lines of white across
the back totally destroy the symmetry of form, while
the white wing-edges fairly force the eye to call them,
not part of a bird sheltering her eggs, but only two among
a myriad irregular edges of coral rock!

Observe closely the seven young Flickers clinging to
their natal stump. As the warriors of Jason sprang forth
from the ground fully armed, so the very bark, mottled



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304 The Bird

with spots of lichen and sunlight, seems to have gendered
these baby birds. Yet they were hatched in a dark hole
from the whitest of white eggs. Is this and a thousand
of other resemblances to be termed accidental? Then
is all Nature one great accident! When the Flicker flies
with swift wing-beat from tree to tree, then the white



Fig. 241. — Laughing Guil on nest.

rump blazes forth. At such moment no protection is
needed; but in these young Flickers upon the tree-trunk,
how exquisitely do their spots deceive the eye! They
are, we say, perhaps sunlight splashes, — nothing more.
Yet others which, like the Brown Creeper, haunt the
tree-trunks of the forest, seem veritably to be but stray
bits of roughened bark creeping here and there.



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306 The Bird

Let us glance at one more bird upon her nest, — a Laugh-
ing Gull. At a distance we see a shapeless blotch of white
sand among the reeds, that is all. We walk over a hundred
other similar patches; but when near enough, we at
last are able to distinguish the dark head and wing-tips,
all but invisible among the shadows, and even through
the centre of the head we can see two spots of light be-
yond, — or no, it is the little subtle ring of white about
the eye!

Two majestic Black-necked Swans may swim closely
along in full view near the opposite bank of a pond, and
yet be totally unrecognizable; showing to the eye as
bodiless necks or neckless bodies, according to the chang-
ing conditions of light and shade around them.

We see a troop of ostriches rushing past. Surely
nothing could hide birds such as these! Again we see
one of these birds prone upon the ground, and a mighty
creature towering eight feet or more above the earth,
becomes naught but a dark ant-hill, which the photo-
graph picks out clearly, but which in the desert, dotted
with ant-hills, would seldom be noticed even by the hungri-
est of lions.

Of course, like most other theories, this of protective
coloration can easily be carried too far, but there are
hundreds of instances where it seems to answer every
requirement of the case. Few fields offer such opportuni-
ties for original work of the most delightful character.
As one example out of untold numbers, what explanation
can we give of the Blood-breasted Pigeon or Bleeding-
heart Pigeon, which, as its name denotes, has a splash



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The Body of a Bird 307



Fig. 243.— Group of Ostriches on the run. (Cawston, photographer.)



Fig. 244. — Ostrich as it hides from an enemy.



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3o8 The Bird

of blood-like scarlet in the centre of its breast? The re-
markable and inexplicable resemblance is heightened
by the stiffened vanes of the centre feathers, causing them
to appear bedraggled and clotted, as if by an actual wound 1
The photograph does but little justice to the bird's real
appearance.

Another class of colours, while still protective, is so
for a purpose very different from those cases which we



Fig. 245. — Bleeding-heart Pigeon.

have been considering. The colours which we are now
to mention have been aptly called aggressive colours, as,
by their means, a bird of prey is enabled to approach
its victim more easily- So, throughout the entire animal
world we find two phases of phenomena constantly pres-
ent: on the one hand the pursued ones, striving to escape
by all means in their power; and on the other hand the
pursuers, ever trjdng to outwit those upon which they
prey. If a duck acquires great speed of flight, the Duck



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The Body of a Bird 309

Hawk must leam to fly still faster. If the duck learns
to crouch close to the reeds when his flight-feathers are
moulted and he is helpless, the hawk must develop
ever sharper eyesight. We may puzzle and puzzle over
a characteristic habit or a colour of some bird, finding
no solution, until we discover some special enemy or
other factor in its life which makes all clear.

So, among aggressive colours we may mention the
garb of the penguin, which is steel-gray on the back and
silvery white below; not to protect it from danger, but
to enable it the better to approach fish without alarming
them. It is curious how fish-like the coloration of these
birds really is, and they are said frequently to lay feet
and tail together and, drawing their flipper-like wings
to their sides, spring clear of the water again and again,
by a single motion of the back muscles, exactly as the
mammalian dolphins leap ahead of a vessel's bow.

Again, while we find the ptarmigan mimicking the
snow in colour, we find the Arctic Fox, the Snowy Owl,
and the Gyrfalcon, all of which are enemies of this bird,
also garbed in white. The ptarmigan may crouch upon
a drift, but it must ever be on the alert, lest from amid
the snowflakes a white death come suddenly upon it.
Nature is terribly just in her plan of life's battles.

In the same region with these lives the Ivory Gull,
immaculate as the ice-floe over which it flies, and in its
whiteness we can perhaps read two purposes: a better
chance to elude the fierce Gyrfalcon, and a better chance
to float cloud-like unperceived over the unsuspecting fish
which it seeks for food.



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Fig. 246.— Black footed Penguin.



Fig. 247. — Pickerel. (Keller, photographer. From life, swimming.)
PREDACIOUS, AQUATIC ANIMALS, SHOWING AGGRESSIVE

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The Body of a Bird 3 1 1

An instance of what has been called unconscious
mimicry seems to exist in the cuckoo of the Old World,
which, like our cowbird, is parasitical in habits, making
no nest of its own, but depositing its eggs in the nests of
other species of birds. The cuckoo bears a striking



Fig. 248. — Ivory Gull. Aggressive and protective coloration in an Arctic Gull.

resemblance to a small hawk, both in general pattern and
in its darting flight. The name Hawk-cuckoo has been
applied to a genus of these birds in India; the name being
given because of the resemblance to a hawk. This simi-
larity may be of great use in temporarily frightening
away the owners of the nest in which the bird wishes



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3 1 2 The Bird

to deposit an egg. A few other instances are known, as
where a fierce, bird-killing hawk resembles a harmless,

insectivorous species,
perhaps by this decep-
tion deluding small
birds.

Many of the plovers
have one, or even two,
bands of black encir-
cling the neck or
breast, and in the
Crook-billed Plover of
New Zealand there is
a most interesting mod-
ification of this ap-
parent ornament. This
bird feeds by running
rapidly around boulders
and inserting its crook-
ed bill beneath them
to obtain the insects

Fig. 249.— Gyrfalcon. Agcressive coloration which COmpoSe its diet.
in an Arctic Hawk.

The pectoral ring of
black, instead of being complete, is said to be often less
developed on the left-hand side. BuUer accounts for this
fact by arguing that that side of the bird is much more
exposed to danger, as it continually scurries about the boul-
ders, keeping always to the right, and thus the side next
to the stone needs no protective colouring; and so we
find this one-sided development of the band. How much,



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The Body of a Bird 3 1 3

in this and in many other so-called protectively coloured
birds, other factors, such as the direct effect of light on



Fig 250.— Snowy Owl. Aggressive coloration in an Arctic Owl.

the plumage, enter into the causation, can only be solved
by future thorough investigation.

Albinos are occasionally found among widely different



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314 The Bird

Families of birds; but white blackbirds and such freaks
of Nature have but slight chance for life when keen-eyed
hawks are ever on the lookout, and owls are alert for
every tell-tale plume. Again and again hawks have been
known to single out white or whitish birds from a number,
making them the object of attack. When any species
of bird, through change of habit, absence of enemies, or
any other cause, is able to increase greatly in numbers,
albinism is likely to occur more frequently. A good ex-
ample of this is to be found in the naturalized English
Sparrows of our cities and towns, among which a remark-
able number with white feathers, or even with the entire
wings and tail white, are to be seen. This is one of
Nature's remedies to reduce the excess number, all need
for protective colours having disappeared in the new
environment of these birds. We may be certain that if,
by any fortunate means, hawks or shrikes can be in-
duced to live within the limits of the cities, the albinistic
individuals will be the first to fall victims.

Black phases of plumage occur among some birds,
and a double colour-scheme is found in the common
Screech Owl, — red and gray individuals being often found
in the same brood, the two phases existing independently
of age, sex, or season.

A vast field for future study and investigation lies in
the meanings of the difi*erences in colour between the
sexes, and in the young birds from both. A hint of the
value of ultimate results in this field (which is without
the scope of this book) is to be found in our young Ameri-
can Robin, whose lower parts, from throat to flanks, are



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Fia. 252. — Young Robin.



Fig. 253. — Fallow Deer fawn one day old.
BOTH SHOWING SPOTS WHICH ARE ABSENT IN THE ADULTS.

316



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The Body of a Bird 317

thickly spotted- This gives a clue to the coloration of its
ancestors, — ^birds probably resembling our Wood Thrush,
and lacking the rufous, immaculate breast of the parents.
We find a similar condition existing among many deer,
whose young are spotted, entirely unlike the brown coats
of their parents.



Fig. 254. — Nestling Turkey Vulture. (T. H. Jackson, photographer.)

In many cases the colouring of the downy young is
the opposite of the adult, as in the Turkey Vulture, the
nestling being clad in down of purest white, and ultimately
moulting into the blackish plumage of the parent birds.

It would be out of place in this volume to speak further
of the wonderful colours which the Class of birds, as a



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3i8 The Bird

whole, exhibits, or of the beautiful plumes which, as
in the case of the Snowy Egret, are assumed only during
the season of courtship. The great majority are now
explained either as decorations to charm the female, or
as mere by-products of the vitality of the bird, according
as to whether one believes in a greater or less degree of
aesthetic appreciation among birds. When we consider
the nervous, high-strung natures of birds and realize with
what ease they are thrown into what seems a kind of
trance, it seems unnecessary to credit them with too great
an appreciation of pure beauty. The repetition of many
similar bright spots, as, for example, the eyes of a pea-
cock's train, may well serve to attract and hold the atten-
tion of the female; while the antics and sounds which
many birds bring into play in courtship may appeal in
some more directly psychic way than we know. That
birds do have a certain appreciation of beauty and har-
mony there can be little doubt. When we remember the


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Online LibraryWilliam BeebeThe bird, its form and function → online text (page 13 of 22)