Nature having thus visually unsubstantialized the bodies of animals, so that, if seen at all, they look flat and ghostly, does not stop there. From solid-shaded bodies they have been converted, as it were, into flat cards or canvases, and, to complete the illusion of obliteration, pictures of the background—veritable pictures of the more or less distant landscape—have been painted on their canvases! Such in effect are the elaborate “markings of field and forest birds.”
Again he writes: “Brilliantly changeable or metallic colours are usually supposed to make the birds that wear them conspicuous, but nothing could be further from the truth. Iridescence is, indeed, one of the strongest factors of concealment. The quicksilver-like intershifting of many lights and colours, which the slightest motion generates on an iridescent surface, like the back of a bird or the wing of a butterfly, destroys the visibility of that wing or back as such and causes it to blend inextricably with the gleaming and scintillating labyrinthine-shadowed world of wind-swayed leaves and flowers.”
According to Thayer, the skunk, which for years has been an important item of the stock-in-trade of the advocates of the theory of warning colouration, is an excellent example of obliterative colouring, since its enemies are supposed to mistake for the sky-line the line of junction between the white fur of the back and the dark fur of the sides. Similarly the crocodiles are supposed to mistake a flamingo for the sky at sunrise or at sunset!
There is doubtless something in this theory of obliterative colouration.
Any one can see, by paying a visit to the South Kensington Museum, that an animal which is of a lighter colour below than above, is less conspicuous in a poor light than it would be were it uniformly coloured. There is then no doubt that this scheme of colour, which is so common in nature, has some protective value.
To this extent has Mr Thayer made a valuable contribution to zoological science. But when he informs us that obliterative colouring is a “universal attribute of animal life,” we feel sorely tempted to poke fun at him.
We would ask all those who believe in the universality of obliterative colouring to observe a flock of rooks wending their way to their dormitories at sunset.