Every one must have observed how many animals escape notice by the similarity of their colours to those of the ground upon which they lie, or of the foliage in which they hide. It is not easy to see rabbits, at dusk, as they sit quietly nibbling the grass upon their sandy warrens. It is difficult, at times, to distinguish a toad from a piece of broken bark or a dead leaf. Moths and butterflies frequently escape pursuit by hiding among twigs and flowers which resemble them in colour. And it is almost impossible to see a shrimp upon the sand of the sea-shore, or a little sandy-coloured fish at the bottom of a sea-side pool. We can hardly doubt that the colours of these animals serve them as a very useful protection. They are all naturally helpless creatures, and their safety depends almost entirely upon their escaping the notice of their enemies.

The examples just given are familiar to us all. But there are few better illustrations of this curious fact than that afforded by the Ptarmigan, a bird which is found in the northern parts of Europe and America, including the north of Scotland. It is a game bird, nearly related to the grouse, the partridge, and even to our domestic fowls, and it is protected, like the other game birds, by Acts of Parliament, which render those who shoot it, during certain months of the year, liable to a fine. The ptarmigan frequents wild, mountainous districts, and builds its nest upon the open hillsides, among the coarse grass and mossy rocks. The nest is a little cluster of twigs and grass, and in it the ptarmigan lays ten or a dozen reddish eggs spotted with brown, which are not easily distinguishable from the twigs and grass among which they lie. The summer plumage of the bird itself is a brown tortoiseshell, so similar in colour to the ground upon which it makes its nest that it is very difficult to see.

In winter-time, however, when the hillsides are covered with snow, the ptarmigan would be easily discovered, if it retained its summer dress. But, upon the approach of colder weather, the bird changes its plumage, and takes on a winter robe of pure white, which makes it just as difficult to detect amidst the snow, as it was in summer when it nested among the grass and stones. With the return of warmer weather it resumes its darker colour. The bird moults, in fact, twice and sometimes thrice in the year. It is impossible to tell the exact cause of these changes, but it is quite certain that they help to protect the bird from its enemies. The change from its winter plumage to its summer one is sometimes delayed for some little time after the winter snows have disappeared, and it has been noticed, in Norway and Sweden, that large numbers of ptarmigan are killed at this time, when their white feathers make them so conspicuous.

The enemies of the ptarmigan are the larger birds of prey, and animals of the weasel kind. One of the largest of the latter is the pine marten, which is still found in remote and uninhabited parts of our country. It is a fierce and active animal, ever on the look-out for game and eggs. It is, in fact, a great poacher, and for this reason it has been practically exterminated by gamekeepers, in all the districts where game is carefully preserved. In other countries the marten is hunted for its skin, the fur of which is scarcely less valuable than that of the sable. It is found in all the northern countries, especially in North America.