Just as every Englishman is of opinion that his house is his castle, so
does every little bird resent all attempts at prying into its private
affairs in the nest. For this reason we really know very little of the
home-life of birds. It is not that there are no seekers after such
knowledge. Practical ornithology is a science that can boast of a very
large number of devotees.
Many men spend the greater part of their life in endeavouring to wrest
from birds some of their secrets, and such must admit that the results
they obtain are as a rule totally disproportionate to the magnitude of
the efforts. At present we know only the vague generalities of bird life.
We know that the hen lays eggs; that she, with or without the help of the
cock, as the case may be, incubates these eggs; that the young, which are
at first naked, are fed and brooded until they are ready to leave the
nest, when they are coaxed forth by the parents, who hold out tempting
morsels of food to them. But these are mere generalities. Our ignorance
of details is very great.
The nests of most passerine birds are scrupulously clean. Young birds
have enormous appetites, and much of the food which they eat is
indigestible and must pass out as droppings, yet in the case of many
species no sign of these droppings is visible, either in the nest, or on
the leaves, branches, or the ground near the nest. What becomes of these
droppings? Ornithological treatises are silent upon this subject.
Again, young birds are born naked, and in India are frequently exposed to
very high temperatures, so that much liquid must pass from their bodies
by evaporation. How is this liquid made good? Do the parents water the
birds, if so, how? I have never seen any mention of this in an
ornithological treatise.
Let us to-day consider these two subjects: the sanitation of the nest and
the method of assuaging the thirst of young nestlings.
As regards the first we have some knowledge, thanks to the patient
labours of Mr. F. H. Herrick, an American naturalist, whose book, _The
Home Life of Birds_, I commend to every lover of the feathered folk.
Unfortunately, Mr. Herrick’s book is to some extent spoiled for
Englishmen, because it deals with birds with which they are unfamiliar;
nevertheless, its general results apply to all passerine birds.
Mr. Herrick is a very keen bird photographer. As every one knows, he who
wishes to obtain good photographs of birds has two great difficulties to
overcome. The first is to get near to his subjects, and the second is to
find them and their nests in situations suitable for photography.
The former is usually overcome by the photographer concealing himself and
his camera in a tent or other structure. At first the birds are afraid of
the concealing object, but soon maternal affection overcomes their fear.
Mr. Herrick’s method of overcoming the second of these two difficulties
is to remove the nest to be photographed from the concealed situation in
which it is usually built, and place it in a more open place. If the nest
be thus moved when the young are some seven or eight days old, the
parents will almost invariably continue to feed their young in the new
situation, for at that particular period the parental instinct is at its
zenith. In addition to obtaining a splendid series of photographs, Mr.
Herrick has observed, from a distance of a few inches, the nesting habits
of several American birds. As the result of these observations he is able
to declare that nest-cleaning follows each feeding with clock-like
regularity. “The excreta of the young,” he writes, “leave the cloaca in
the form of white opaque or transparent mucous sacs. The sac is probably
secreted at the lower end of the alimentary canal, and is sufficiently
consistent to admit of being picked up without soiling bill or fingers.
The parent birds often leave the nest hurriedly bearing one of these
small white packages in bill, an action full of significance to every
member of the family. . . . Removing the excreta piecemeal and dropping
it at a safe distance is the common instinctive method, not only of
insuring the sanitary condition of the nest itself, but, what is even
more important, of keeping the grass and leaves below free from any sign
which might betray them to an enemy.” These packets of excrement are
quite odourless, and they are often devoured by the parent bird instead
of being carried away. The digestion of very young birds must be feeble,
and doubtless much of the food given them passes undigested through the
alimentary canal, so that it is capable of affording nourishment to the
parents. Birds are nothing if not economical.
Of course, all birds are not so careful of the sanitation of the nest.
Every one knows what a filthy spectacle a heronry is. According to Mr.
Herrick, the instinct of inspecting and cleaning the nest is mainly
confined to the great passerine and picarian orders. It is obviously not
necessary in the case of those birds, such as fowls, of which the young
are able to run about when born; nor is it needful in the case of birds
of prey, who take no pains to conceal the whereabouts of the nest. Young
raptores eject their semi-fluid excreta over the edge of the nursery;
thus the nest is kept clean, but the droppings on the ground betray its
presence to all the world.
Coming now to our other question: How do young birds obtain the water
which they require? we have no help from Mr. Herrick. He makes no mention
of this in his most interesting book. It is possible that nestlings are
not given anything to drink, that the juicy, succulent insects or fruits
with which they are supplied contain sufficient moisture for their
requirements. We must remember that the skin of birds is very different
from that of man. It contains no sweat glands, so that a bird, like a
dog, can only perspire through its mouth.
The breath of mammals is so surcharged with moisture that when it is
suddenly cooled the water vapour in it condenses; the result is we can
“see the breath” of a mammal on a cold day. I have never succeeded in
seeing a bird’s breath, so am of opinion that the fowls of the air do not
exhale so much moisture as mammals do. But even allowing for this, a
considerable amount of moisture must be given out in expiration, so that
it seems probable that young birds require more moisture than they obtain
in their food. Drops of water have to be administered to hand-reared
birds. Many birds fill up the crop with food and then discharge the
contents into the gaping mouths of their young. In this condition the
food must be mixed with a considerable quantity of saliva and possibly
with water. The crop of a bird is a receptacle into which the food passes
and remains until actually utilised. There seems no reason why water
should not be stored for a short time in this receptacle just as food is.
Perhaps birds “bring up” water as they do solid food, and thus assuage
the thirst of their young. Such a process would be very difficult to
detect; it would be indistinguishable from ordinary feeding to the casual
observer. I hope that some physiologist will take up the matter. A
quantitative analysis of the air exhaled by a bird should not be very
difficult to make.