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_.