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we have probably thought that a similar habit was being
shown, — ^half -digested grain taking the place of the
heron's fish. But such is not the case. At the time
of the breeding season, the folds of membrane in the
crops of both parent pigeons thicken and secrete or
peel ofiF in curdy cheesy masses — ^'pigeon's milk" some
call it— and this forms the food of the young birds So
in pigeons the crop not only receives food, but at times
provides it.

Now for a glance at some of the oddities in the struc-
ture of crops. The Hoatzin — a strange bird of Brazilian
swamps — which harks back to its reptilian ancestors in
many ways, has a very curious crop. There are strong
muscles in its walls, the use of which, it is said, is to

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Organs of Nutrition 131

squeeze out the juice of the thick leaves of the Arum
arborescens which forms its food- Thus it has a gizzard-
like function, and has become so important in the life-
economy of the bird that it has developed out of all
proportion, and occupies so much space that the keel
on the breast-bone has had to give way in part to make
room for it, and even the arms of the "wish-bone'' have
been bent outward- In this remarkable bird the pro-
ventriculus and gizzard are reduced, their functions being
usurped by the crop.

The facility with which most birds are able to eject
the contents of their crops serves several useful pur-
poses, besides the feeding of the young of herons, cor-
morants, and others. When vultures have gorged them-
selves to repletion on the flesh of any animal, they usually
retire to some near-by retreat and sleep until digestion
has taken place. But if they are suddenly approached
or alarmed, they will instantly eject all they have swal-
lowed and, thus lightened, take safety in flight. Pelicans
and Wood Ibises also have the habit of *uns wallowing'
their fishy meals when frightened. Petrels and many
fish-eating sea-birds appear to have a supply of oil always
in readiness, which they shoot from the mouth to a con-
siderable distance, surving as an efficient means of self-
defence when taken in the hand after being wounded.

In birds of prey generally, but especially in owls,
another use for this habit is found. Owls always swallow
their smaller prey entire, sometimes crushing the skulls
of mice and plucking out the longer wing and tail-feathers
of birds. Although their crops are not nearly so mus-

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132 The Bird

cular as that of the Hoatzin, yet there must be powerful
movements of the walls, for the mice and birds are de-
nuded of hair and feathers and even the bones are in
some way removed from the body, and all are ejected
in a neat oval ball.

If we find some hollow tree where an owl has its

Fig. 103.— Keel of Hoatzin, repressed by crop.

regular sleeping-place, many of these pellets may be
found on the ground below, showing the results of each
night's hunting. The skulls in them are often in such
perfect condition that the species of rodents may be
identified. Besides allowing the bird conveniently to get
rid of the indigestible portions of its food, this habit
seems to be necessary to the health of the bird. In

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Organs of Nutrition 133

captivity, owls and hawks are never so healthy and active
when fed on fleshy meat alone, as when a dead mouse or
sparrow, rat or pigeon is given occasionally. In dissecting
specimens which have had nothing but a flesh diet for a
year or more, I have found the throat and gullet in a very
bad condition, as if the lack of some scouring process,

Fig. 104. — Food-pellets ejected by Great Horned Owl, containing
remains of rodents.

such as is afforded by the pasage up and down of the
indigestible hair and feathers, had actually resulted in
the death of the bird. I have seen owls try to eat the
straw on the floors of the cages, when not provided with
food in the condition in which they find it when at lib-

In cormorants and birds of similar voracious fish-eating
habits, the entire gullet serv^es as a receptacle for food,
while the fish first swallowed are undergoing the process

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134 The Bird

of digestion lower down. Here, as in many other in-
stances, we have a condition very similar to that in some
reptiles — crocodiles in particular. These ravenous scaly
creatures have such powerful organs of digestion that even
bones are dissolved, but the stomach is comparatively
small, and when a crocodile makes a large meal, it is at
first stored away in the wide gullet.

The Stomach and Gizzard

In the present chapter we might easily be led into

details which would strand
us in the midst of dry
technicalities, but we will
try to avoid all this and
choose only the interesting

The chief organ of di-
gestion, in birds as in other
animals, is of course the
stomach. In many fish-
eating birds this organ is
merely a simple, more or
less enlarged chamber, rather
crop-like except that it con-
tains numerous digestive

"""• ''' - STwitter ""'' "^- The typical bird-stom-

ach, however, is compound,

or formed of two more or less distinct parts. The first

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Organs of Nutrition 135

portion — known as the proventriculus — is the smaller, and
contains very active digestive glands, sometimes ar-
ranged in patches, but more usually forming a band. If
the lower part of the oesophagus of an English Sparrow
is removed, slit open and washed, these glands can be
easily seen, being more of a rose tint than the paler tissue
of the portion nearer the mouth. The walls are thicker
in this glandular area. This can be seen to better ad-
vantage in a young chicken,
where the glands take the
form of conical protuber-
ances which dot the entire
surface. Nature has pro-
duced curious modifications
of this typical fore-stomach,
as in snake-birds, which have
the glands of this portion en-
closed in a sac, in shape not
unlike a small crop. Here
the food is softened and acted
Fig. 106.— Glands of the stomach of a upon chemically by the secre-

young chicken. . - , , , ,

tions from the walls.
The second division of the stomach is the gizzard,
an organ made ^ to perform most powerful compressing
motions, thus crushing and macerating the food, so that
when passed on into the intestine, every particle of nour-
ishment may be extracted from it. When we think of
beauty of colouring in birds, it is their plumage which
at once presents itself to the mind, and yet a gizzard
has a real beauty both of shape and hue. This organ.

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I 36 The Bird

in a chicken, is in shape like a double convex lens. The
cavity in the centre is lined with a tough yellow membrane,
sometimes almost as hard as bone. Two great tendons
spread over the outer surface on each side, and although
in life forever buried in the absolute darkness of the
bird's body, yet when brought into sunlight they shine
with an iridescence like the beam from a spectrum.

It is hardly possible for the gizzard to grind up food
in the sense of having much lateral motion, like the move-
ment of the jaws in chewing, but it shuts together again
and again with great force. Gravel and sharp stones are
swallowed by many birds, and are of great importance
in helping to grind the food. The number and size of
these stones are sometimes almost beyond belief. I
have known a cassowary to swallow over a quart of rubble
in one day, and have given a quartz pebble twice as large
as a hen's egg to one of these birds and watched it slip
down the bird's throat as easily as a cube of carrot. This
particular bird preferred smooth white quartz pebbles,
and would search through a whole heap, picking out stones
of this character. The same preference was exhibited
by the gigantic extinct birds of New Zealand called moas.

Mr. Frederick Chapman, writing of a portion of New
Zealand where the skeletons of moas were found in great
abundance, says: **VVhen we came upon the ground
disturbed by the wind (the soil being shifting sand)
we soon found a number of distinct groups of gigantic
gizzard-stones. It was impossible to mistake them. In
several cases they lay with a few fragments of the heavier
bones. In all cases they were in distinct groups; even

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Organs of Nutrition 137

where they had become scattered, each group covered
only a few square yards of ground, and in that space
lay thickly strewn. . . . The peculiar feature of the
stones was that they were almost all opaque, white quartz
pebbles. In one place I found a small group of small
pebbles of dijfferent colour, more like the few brown water-
worn pebbles which may be picked up hereabouts. These
lay with a set of bones much smaller than the very large
bones I found with most of the clusters of pebbles.

*'I did not gather these brown pebbles, as I thought
it uncertain whether they were gizzardnstones or not,
though it is possible that the species to which the smaller
stones belonged was not so careful in selecting white

*'A glance at the pebbles lying around in the sur-
rounding country showed that the quartz-pebbles were
not collected here. . . . Mr. Murdock and I collected
three sets of pebbles, and these I can pronounce com-
plete, or nearly so. It is beyond question, too, that each
set belongs to a distinct bird. No. 1 weighs 3 lb. 9 oz.;
No. 2 weighs 4 lb.; while No. 3 weighs no less than 5 lb.
7 oz.! This giant set contains individual stones weighing
over 2 oz.; indeed, I have picked out eight stones weigh-
ing almost exactly 1 pound.''

The gizzard of a bird is reflective of its diet, and is
very quickly affected by any change in the food. For
example, a captive gull when fed exclusively on fish
has but little muscular power in the gizzard, but a diet
of grain will produce a change in that organ, giving it
grinding power sufficient to crush the kernels of corn.

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138 The Bird

That this is something more than an abnormal con-
dition brought about by artificial means is proved by
the fact that in the Orkney Islands the wild gulls feed
in winter, spring, and summer on fish, and at this time
are gizzardless; but in the fall they change to a diet of
corn and develop a very respectable gizzard. So we
see that this organ, apparently so independent in func-
tion and individual in appearance in many birds, is in
reality only a physiological change from the stomach

The history of the development of this organ may
be traced in various living species, from the soft mem-
branous sac of a fish-eating bird to the knot of tendons
which forms the gizzard of certain Fruit-pigeons. These
birds feed on nutmegs and other very hard, almost stony
nuts, and to enable the bird to crush these, the lining of
the gizzard is covered with several score of conical pro-
jections, horny in consistence. These are probably the
nearest approach to ''hen's teeth "we are likely to find.

What a boon to a business man who indulges in a
daily "fireman's lunch," if his masticatory function
could be an internal and unconscious one, as in a bird!

A crocodile, which has so much in common with a
bird, is provided with a gizzard, which, like that of a
chicken, is round, muscular, and has two great side ten-
dons, and no less than five pounds of grinding-stones
have been found in one of these reptiles.

Many interesting adaptations are found in the stom-
achs of birds, made necessary by special requirements
in the diet. As an instance of this, the snake-bird has

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Organs of Nutrition i 39

a dense mat of hair at one end of the stomach, the free
ends of which point outward, brush-like, and prevent
the accidental entrance of any small fish-bones which
otherwise might get into the small intestine. The giz-
zard of a cuckoo, when opened, often gives the impression
of a similar coating of hair lining the entire organ, but
these are in reality only the hairs of caterpillars upon

Fig. 107. — Cluster of matted hairs in the stomach of a Snake-bird.

which these birds feed, which have become detached
and have lodged in the folds of the gizzard lining.

When considering the crops of birds we noticed the
curious way in which a pigeon feeds its young, by re-
gurgitating a cheesy substance which forms in its crop,
and we will now speak of something still more remark-
able. The strange nesting habits of the hornbills are
foreign to this volume, but we cannot leave the subject
of gizzards without touching on the manner in which
the male birds of this group probably feed their impris-

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140 The Bird

oned mate and young. I say probably, because no one
has seen them do this, but as in captivity the operation
occurs repeatedly during the breeding season, there can
be but little doubt concerning its evident significance.
After walling up his mate and her egg in some hollow
tree, the male hornbill takes upon himself the labour of
supplying her with food throughout the period of incu-
bation and the subsequent rearing of the young bird.
Instead of bringing food piecemeal, — nut by nut, grape
by grape, — the lining of the entire gizzard peels off at
certain frequent intervals, appearing, when ejected at
the mouth, like a small bag or purse, the puckered open-
ing (heightening the simile) serving to retain securely
the contents of the gizzard, — a dozen or score of grapes
or other fruit. This, the male bird, in his native land,
doubtless takes in his beak to the tiny opening of the
walled-up nest and delivers into the bill of his mate.
How admirable a spouse this, who not only seeks and
provides sufficient food for his temporarily helpless
family, but bears it to them wrapped in a packet torn
from his very body — if not a *' pound of flesh,'' at least
enough to make a lunch-basket!

The Intestines

Beyond the gizzard is the intestinal capal, which
varies greatly in length in different birds. The ostrich
has forty-six feet of this digestive tube, while the nectar
and tiny insects snatched by a hunmiingbird in its flight
are digested in a delicate hair-like duct but two inches in
length. Although comparatively of such great length, the

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Organs of Nutrition 141

way in which this part of the digestive tract is coiled and
twisted in the body cavity of the bird allows it to take
up the least possible amount of room.

The function of this long tube is to absorb the nutri«
ment from the food after this has been moistened by
the salivary glands, crushed by the gizzard, and acted
on by the stomach acids, and secretions from the liver
and pancreas. The digestible parts are then taken up
by the blood through the walls of the intestine. In
many of the lower types of birds, such as the cassowary,
ostrich, and screamer, the arrangement of this long
digestive tract is very simple, much like the condition
to be found in alligators.

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HE organs and physiological functions of a bird,
as of animals generally, are so interrelated and
intimately dependent on each other that it is a
rather difficult matter to consider any single one by
itself without being led into another's province. For
example: we have for the subject of this chapter the
food of birds, and unless we are very careful, we shall
overstep the bounds of our theme. To limit our subject
clearly we will consider only adult birds.

We have all seen the pestiferous sparrows picking
up grain in the chicken-yard; we have admired the skill
which the red-breasted robin exhibits in spying and
extracting earthworms on our lawns; our memory re-
calls the osprey dropping upon his fish, and the wood-
pecker chiselling to the wood-borer; but did we ever stop
a while and attempt a ^^ bird's-eye view" of all the classes
of substances which birds find good as food?

The ways in which this food is sought and caught,

killed and prepared are wonderfully varied, and some

idea of the remarkable variety of substances laid under

contribution as food by birds of different orders may

be had from a brief review of the principal divisions


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The Food of Birds 143

into which these substances axe classified, and the part
they take in supplying birds with food.

As with all animals, certain mineral salts are very
necessary to a bird^s existence, such as the substances
from which the calcium phosphate for the bones, and
the calcium carbonate for the shells of the eggs, are de-

FiG. 108. — Finch, a bird with heavy, thick bill adapted for crushing seed.

rived. The gravel and pebbles swallowed by birds in
the course of their daily feeding should hardly be men-
tioned in this connection, as this is only done for the
mechanical assistance, derived from the hard surfaces,
in triturating the food.

Vegetable-feeders form a large group among birds, and
they alone would offer an interesting field for study, as

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144 The Bird

there is such specialization for feeding on particular
varieties or portions of plants. We find fruit- and grain-
eaters, besides those which feed almost entirely on buds,
leaves, berries and nuts, nectar, sap, and even pollen.
Lichens form a considerable item in the bill of fare of
ptarmigans, the Arctic grouse. We have even dedicated
certain plants to birds which show a decided partiality
for them, — duckweed and partridge-berry.

Fig. 109. — Vireo, an insect-hunter, with a delicate, hooked bill.

There is no doubt that a great many plants benefit
from the cross-fertilization of their flowers by humming-
birds carrying the pollen from blossom to blossom. Of
one of the sugar-birds of South Africa it is said: '* When
sucking up the nectar of one of the larger protea-blossoms,
the bird perches on the edge of the flower, plunges its
long bill and the greater part of its head downwards
among the petals, and retains it in this position until

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The Food of Birds 145

satisfied. As a result the narrow, shaft-like feathers of
the forehead frequently become saturated and stained
with juice and dusted over with pollen, and it is probable
that this bird plays an important part in the cross-fer-
tilization of several species of protea."

Desmids and diatoms, those one-celled microscopic
organisms which are almost on the border-line between


Fig. 110.— Sea-urchin.

plants and animals, I have found in large numbers in
the digestive tracts of ducks and other birds which are
accustomed to find their food by sifting the mud at the
edges of ponds and lakes.

Sponges, at least in a decayng state, are devoured by
crows, as I can testify from observation after dredging
expeditions in the Bay of Fundy.

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146 The Bird

We should scarcely think that those watery creatures
sea-anemones, hydroids, and jelly-fish (some of the latter

Fig. 111.— Caterpillar.

consisting of over 95 per cent water) could afford much
nourishment to any animal, and when crows and gulls
are seen tearing large stranded jellies into pieces, it is

Fig. 112.— Cocoon.

probably only for the sake of the semi-parasitic shrimps
which make their home in the interior canals of the

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The Food of Birds 147

masses of animate gelatine. But the fresh-water hydra,
belonging to the same division as the hydroids, is eaten
in myriads by ducks and geese. These and many other
birds are remarkably fond of duckweed, which they
devour with such evident pleasure that they must enjoy
it as much as cats do catnip, or canaries hempseed. As
the under surface of these small water plants is the fa-

FiG. 113.— Butterfly with wing torn by bird.

vourite home of the hydra, they necessarily form a por-
tion of the food of these water birds.

Roundworms, flatworms, and leeches are devoured
by many aquatic birds, while earthworms form a staple
article of diet with such different species as thrushes,
woodcocks, and cranes. A favourite morsel of the curi-
ous apteryx of New Zealand is a gigantic species of worm,
twelve to twenty inches in length, which is highly phospho-
rescent. The apterj^x seeks its food by night, and when

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148 The Bird

devouring one of these worms, the whole bird is lighted

up, and after its meal the bird's bill is illumined by the

mucus which adheres to it.

Starfish and sea-urchins are sought out by crows,

ravens and gulls, and perhaps other birds. They break

into them by main force, or
else carry them to a height
and drop them on the rocks.
I have even seen a Bald
Eagle, when fish and Fish-
hawks were scarce, deliber-
ately break into and devour
a green-spined urchin.

K, as is said, immense bow-
head whales subsist entirely

Fig. I14.-Snail. ^^ ^^^^^^^ j^^^^j shrfmps,

then it is not surprising that many thousands of shore-
birds are well nourished by the myriads of shrimps and
prawns, large and small, which every tide leaves exposed.
It is a mere truism to say that insects form the sole
food of scores of species of birds, and enter into the diet
of many hundreds. It has been said that without birds,
within a space of ten years, the earth would not be habit-
able for man, owing to the unrestricted increase of nox-
ious insects. There is doubtless not a single group of in-
sects which does not suffer from the appetite of one or
more species of bird. The eggs and larvae are dug and
pried out of their burrows in the wood by woodpeckers
and creepers; those underground are scratched and
clawed up to view by quail, partridges, and many spar-

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The Food of Birds


rows; warblers and vireos scan every twig and leaf;
flycatchers, like the cat family, lie in watch and spring
after their prey, only in the air instead of on the ground,
feeding more particularly on low-flying insects; while
swifts, swallows, and martins glean their harvest from the
diurnal hosts of high-flying winged creatures. Many

Fig. 115— Crab.

times when we think hummingbirds are taking dainty
sips of nectar from the flowers, they are in reality pick-
ing minute spiders and flies from the deep cups of the co-
rollas. When night falls, the insects which have chosen
that time as the safer to carry on their business of life
are pounced upon by nocturnal feathered beings — the
cavernous mouths of the whippoorwills engulf them as
they rise from their hiding-places, and the bristles of

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150 The Bird

night-hawks brush them into rapacious maws, if per-
chance they have succeeded in reaching the upper air.

In tropical forests, where insects are everywhere
abundant, the birds seemed to have realized the fact that
to each is apportioned certain phases of insect life, and
that by hunting in large flocks, instead of competition
resulting between birds of different species, they play
into each other's hands (or rather beaks). It is of such
a flock that Hudson writes: "The larger creepers ex-

Fio. 116.— Squid.

plore the trunks of big trees, others run over the branches
and cling to the lesser twigs, so that every tree in their
route, from its roots to the topmost foliage, is thoroughly
examined, and every spider and caterpillar taken, while
the winged insects, driven from their lurking-places, are
seized where they settle, or caught flying by the tyrant-

The Wattled Starlings or Locust-birds of South Africa
live in flocks of thousands, and so dependent are they
on locusts as food, that their habitat and place of nest-

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The Food of Birds


ing is influenced by the presence or absence of these in-
sects. "When pursuing a flight of mature locusts these
starlings perform various extraordinary and beautiful
aerial evolutions with the object of intercepting and sur-
rounding a portion of the swarm, and in doing this their
movements closely resemble those of another locust-
destroying starling, the beautiful rose-coloured Pastor
of eastern Europe and Asia, Individually the two species
are very different; collectively and under similar condi-
tions their actions are quite
similar. Starting in a dense
' ball-like ' mass, they suddenly
open out into a fan-shaped
formation, then assume a
semicircular arrangement, and
finally end by forming a
hollow cylinder in which a
portion of the locusts are
enclosed; as the imprisoned

insects are destroyed, the f,q. in.-Rattiesnake.

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Online LibraryWilliam BeebeThe bird, its form and function → online text (page 7 of 22)