The drongo cuckoo (_Surniculus lugubris_) is a bird of which I know
practically nothing. I doubt whether I have ever seen it in the flesh. It
is, of course, quite unnecessary to apologise for discoursing upon a
subject of which one’s knowledge is admittedly _nil_. In this superficial
age the most successful writers are those most ignorant of their subject.
When you know only one or two facts it is quite easy to parade them
properly, to set them forth to best advantage. They are so few and far
between that there is no danger of their jostling one another or
bewildering the reader. Then, if you are conversant only with one side of
a question, you are able to lay down the law so forcibly, and the public
likes having the law laid down for it, it does not mind how crude, how
absurd, how impossible one’s sentiments are so long as one is cocksure of
them and is not afraid to say so.
My lack of knowledge of the habits of the drongo cuckoo is, however, not
my chief reason for desiring to write about it. I wish to discuss the
bird because natural selectionists frequently cite it as bearing striking
testimony to the truth of their theory, whereas it seems to me that it
does just the opposite. _Surniculus lugubris_ is, so far as I am able to
judge, an uncompromising opponent of those zoologists who pin their faith
to the all-sufficiency of natural selection to account for evolution in
the organic world.
The drongo cuckoo is as like the king-crow as one pea is to another. This
bird, says Blanford, “is remarkable for its extraordinary resemblance in
structure and colourisation to a drongo or king-crow (_Dicrurus_). The
plumage is almost entirely black, and the tail forked owing to the
lateral rectrices being turned outwards.” Blanford further declares that
the bird, owing to its remarkable likeness to the king-crow, is apt to be
overlooked.
This being so, it is quite unnecessary for me to describe the drongo
cuckoo; it is the image of a king-crow. But stay, perhaps there are some
who do not know this last bird by sight. Such should make its
acquaintance. They will find it sitting on the next telegraph wire they
pass—a sprightly black bird, much smaller than the crow (with which it
has no connection), possessing a long, forked tail. Every now and again
it makes little sallies into the air after the “circling gnat,” or
anything else insectivorous that presents itself. When you see such a
bird you may safely bet on its being a king-crow; the off-chance of its
proving a drongo cuckoo may be neglected by all but the ultra-cautious.
Not much is known of the habits of this cuckoo; but what we do know shows
that, sometimes, at any rate, it makes the king-crow act as its
nursemaid. Mr. Davison saw two king-crows feeding a young _Surniculus_.
The consequence is that every book on natural history trots out our
friend the drongo cuckoo as an example of mimicry. The mimicry is, of
course, unconscious: it is said to be the result of the action of natural
selection.
King-crows are, as every one knows, exceedingly pugnacious birds; at the
nesting season both cock and hen are little furies, who guard the nursery
most carefully and will not allow a strange species to so much as perch
in the tree in which it is placed.
It is thus obvious that the cuckoo who elects to victimise a king-crow is
undertaking a “big thing,” yet this is what _Surniculus_ does. It
accomplishes its aim by trickery; it becomes a gay deceiver, disguising
itself like its dupe. Now I readily admit that the disguise may be of the
utmost use to the _Surniculus_; I can well understand that natural
selection will seize hold of the disguise when once it has been donned
and possibly perfect it; but I cannot see how natural selection can have
originated the disguise _as such_.
The drongo cuckoo may be called an ass in a lion’s skin, or a lion in an
ass’s skin, whichever way one looks at things. When once the skin has
been assumed natural selection may modify it so as better to fit the
wearer; but more than this it cannot do.
I do not pretend to know the colour of the last common ancestor of all
the cuckoos, but I do not believe that the colour was black. What, then,
caused _Surniculus lugubris_ to become black and assume a king-crow-like
tail?
A black feather or two, even if coupled with some lengthening of the
tail, would in no way assist the cuckoo in placing its egg in the
drongo’s nest. Suppose an ass were to borrow the caudal appendage of the
king of the forest, pin it on behind him, and then advance among his
fellows with loud brays, would any donkey of average intelligence be
misled by the feeble attempt at disguise? I think not. Much less would a
king-crow be deceived by a few black feathers in the plumage of a cuckoo.
I do not believe that natural selection has any direct connection with
the nigritude of the drongo cuckoo. It is my opinion that, so far as the
struggle for existence is concerned, it matters little to an animal what
its colour be. Every creature has to be some colour: what that actual
colour is must depend upon a great many factors; among these we may name
the metabolic changes that go on inside the animal, its hereditary
tendencies, sexual selection, and natural selection. Is it natural
selection that has caused the king-crow to be black? I trow not.
The drongo is black because it is built that way; its tendency is to
produce black feathers. Just as some men tend to put on flesh, so also
some species of birds tend to grow black plumage. In the case of the
king-crow sexual selection has possibly contributed to the bird’s
nigritude. It is possible that black is a colour that appeals to
king-crow ladies. “So neat, you know; a bird always looks well in black,
and a forked tail gives him such an air of distinction.”
As the hen drongo is a bird capable of looking after herself, even when
incubating, there is no necessity for her to be protectively coloured. As
I have repeatedly declared, one ounce of good solid pugnacity is a better
weapon in the struggle for existence than many pounds of protective
colouration.
Again, in the case of king-crows nigritude may be an expression of
vigour, the outward and visible sign of strength.
Let me make myself clear. Suppose that in a race of savages those that
had fair hair were stronger, bolder, more prolific, and more pushing than
the dark-haired men. Fair hair, in some inexplicable way, always
accompanied strength and the like. It is obvious that, under these
conditions, the race would in time become fair-haired: the milder dark
men would eventually be hustled out of existence. Fair hair would then be
the outward expression of vigour: it would not be the cause of vigour,
merely the accompaniment of it; nor would it be a direct product of
natural selection. In the same way it is possible that among drongos
nigritude is in some manner correlated with vigour. This idea is not
altogether fanciful. Are there not horses of “bad colour”? Are not white
“socks” a sign of weakness? Is not roan a colour indicative of strength
and endurance in a horse?
May not the blackness and the forked tail of the drongo cuckoo have
arisen in the same way as they arose in the king-crow? In each case it
may be an accompaniment of vigour, or it may be the result of sexual
selection. Mrs. Surniculus may have had similar tastes to Mrs. Dicrurus,
and, since cuckoos seem to be very plastic birds, her tastes have been
gratified. As another example of this plasticity I may cite _Centropus
phasianus_—a cuckoo which is a very fair imitation of a pheasant.
On this view the resemblance is a mere chance one. The cuckoo is not an
ass in a lion’s skin, but an ass that looks very like a lion. His
lion-like shape was not forced upon him by natural selection. A variety
of causes probably contributed to it. It was not until the resemblance
had arisen and become very striking that it was directly affected by
natural selection.
I am far from saying that the above is a correct explanation of the
nigritude: it is all pure hypothesis. Even if it be correct, we are
really very little further than we were before towards an explanation of
the colours and shape of either the king-crow or the drongo cuckoo.
Why did these birds tend to grow black feathers rather than red, green,
or blue ones?
This is a question which “stumps” us all.