What a great difference there is in brilliancy of colouring between birds
and the furry creatures. How the plumage of a cardinal, or indigo bunting,
or hummingbird glows in the sunlight, and reflects to our eyes the most
intense vermilion or indigo or an iridescence of the whole gamut of
colour. On the other hand, how sombrely clad are the deer, the rabbits,
and the mice; gray and brown and white being the usual hue of their fur.
This difference is by no means accidental, but has for its cause a deep
significance,--all-important to the life of the bird or mammal. Scientists
have long known of it, and if we unlock it from its hard sheathing of
technical terms, we shall find it as simple and as easy to understand as
it is interesting. When we once hold the key, it will seem as if scales
had fallen from our eyes, and when we take our walks abroad through the
fields and woods, when we visit a zoological park, or even see the animals
in a circus, we shall feel as though a new world were opened to us.
No post offices, or even addresses, exist for birds and mammals; when the
children of the desert or the jungle are lost, no detective or policeman
hastens to find them, no telephone or telegraph aids in the search. Yet,
without any of these accessories, the wild creatures have marvellous
systems of communication. The five senses (and perhaps a mysterious sixth,
at which we can only guess) are the telephones and the police, the
automatic sentinels and alarms of our wild kindred. Most inferior are our
own abilities in using eyes, nose, and ears, when compared with the same
functions in birds and animals.
Eyes and noses are important keys to the bright colours of birds and
comparative sombreness of hairy-coated creatures. Take a dog and an oriole
as good examples of the two extremes. When a dog has lost his master, he
first looks about; then he strains his eyes with the intense look of a
near-sighted person, and after a few moments of this he usually yelps with
disappointment, drops his nose to the ground, and with unfailing accuracy
follows the track of his master. When the freshness of the trail tells him
that he is near its end he again resorts to his eyes, and is soon near
enough to recognise the face he seeks. A fox when running before a hound
may double back, and make a close reconnaissance near his trail, sometimes
passing in full view without the hound's seeing him or stopping in
following out the full curve of the trail, so completely does the
wonderful power of smell absorb the entire attention of the dog.
Let us now turn to the oriole. As we might infer, the nostrils incased in
horn render the sense of smell of but slight account. It is hard to tell
how much a bird can distinguish in this way--probably only the odour of
food near at hand. However, when we examine the eye of our bird, we see a
sense organ of a very high order. Bright, intelligent, full-circled, of
great size compared to the bulk of the skull, protected by three complete
eyelids; we realise that this must play an important part in the life of
the bird. There are, of course, many exceptions to such a generalisation
as this. For instance, many species of sparrows are dull-coloured. We must
remember that the voice--the calls and songs of birds--is developed to a
high degree, and in many instances renders bright colouring needless in
attracting a mate or in locating a young bird.
As we have seen, the sense of smell is very highly developed among
four-footed animals, but to make this efficient there must be something
for it to act upon; and in this connection we find some interesting facts
of which, outside of scientific books, little has been written. On the
entire body, birds have only one gland--the oil gland above the base of
the tail, which supplies an unctuous dressing for the feathers. Birds,
therefore, have not the power of perspiring, but compensate for this by
very rapid breathing. On the contrary, four-footed animals have glands on
many portions of the body. Nature is seldom contented with the one primary
function which an organ or tissue performs, but adjusts and adapts it to
others in many ingenious ways. Hence, when an animal perspires, the pores
of the skin allow the contained moisture to escape and moisten the surface
of the body; but in addition to this, in many animals, collections of
these pores in the shape of large glands secrete various odours which
serve important uses. In the skunk such a gland is a practically perfect
protection against attacks from his enemies. He never hurries and seems
not to know what fear is--a single wave of his conspicuous danger signal
is sufficient to clear his path.
In certain species of the rhinoceros there are large glands in the foot.
These animals live among grass and herbage which they brush against as
they walk, and thus "blaze" a plain trail for the mate or young to follow.
There are few if any animals which care to face a rhinoceros, so the scent
is incidentally useful to other creatures as a warning.
It is believed that the hard callosities on the legs of horses are the
remains of glands which were once upon a time useful to their owners; and
it is said that if a paring from one of these hard, horny structures be
held to the nose of a horse, he will follow it about, hinting, perhaps,
that in former days the scent from the gland was an instinctive guide
which kept members of the herd together.
"Civet," which is obtained from the civet cat, and "musk," from the queer
little hornless musk deer, are secretions of glands. It has been suggested
that the defenceless musk deer escapes many of its enemies by the
similarity of its secretion to the musky odour of crocodiles. In many
animals which live together in herds, such as the antelope and deer, and
which have neither bright colours nor far-reaching calls to aid straying
members to regain the flock, there are large and active scent glands. The
next time you see a live antelope in a zoological park, or even a stuffed
specimen, look closely at the head, and between the eye and the nostril a
large opening will be seen on each, side, which, in the living animal,
closes now and then, a flap of skin shutting it tight.
Among pigs the fierce peccary is a very social animal, going in large
packs; and on the back of each of these creatures is found a large gland
from which a clear watery fluid is secreted. Dogs and wolves also have
their odour-secreting glands on the back, and the "wolf-pack" is
proverbial.
The gland of the elephant is on the temple, and secretes only when the
animal is in a dangerous mood, a hint, therefore, of opposite significance
to that of the herding animals, as this says, "Let me alone! stay away!"
Certain low species of monkeys, the lemurs, have a remarkable bare patch
on the forearm, which covers a gland serving some use.
If we marvel at the keenness of scent among animals, how incredible seems
the similar sense in insects--similar in function, however different the
medium of structure may be. Think of the scent from a female moth, so
delicate that we cannot distinguish it, attracting a male of the same
species from a distance of a mile or more. Entomologists sometimes confine
a live female moth or other insect in a small wire cage and hang it
outdoors in the evening, and in a short time reap a harvest of gay-winged
suitors which often come in scores, instinctively following up the trail
of the delicate, diffused odour. It is surely true that the greatest
wonders are not always associated with mere bulk.