The red grouse is placed in a genus called "Lagopus," of which there are several species in the northern hemisphere. In Scotland the red grouse, which is distinguished as Lagopus Scoticus, is accompanied by a rarer species of Lagopus, which lives in high, bare regions. This is the bird called by the Celtic name "ptarmigan"; it differs in several points from the red grouse, and acquires white plumage in the winter, which the latter bird does not; it is called Lagopus mutus. Now in Norway we find also two species of grouse or Lagopus, called "rypé" (pronounced "reeper") by the Norwegians. One is the same bird in every respect as the Scotch ptarmigan, and is known as "the mountain rypé." The other is very close to our red grouse, and is called "the common or bush rypé," and by English naturalists the "willow grouse," and by ornithologists "Lagopus salicetus." It agrees in habits, voice, eggs, and anatomical detail with our red grouse, but the back of the cock-bird of the red grouse and the whole plumage of the hen-bird have a darker colour. Moreover, the willow grouse, like the ptarmigan or mountain rypé, turns white–acquires a white plumage–in the winter which the red grouse does not. Are the red grouse and the willow grouse to be regarded as distinct species? Our British red grouse lives on heather-grown moors; the willow grouse prefers the shrubby growths of berry-bearing plants interspersed with willows, whence its name. Their food differs accordingly. Formerly the red grouse lived on the moors of the South of England, and when in Pleistocene times England was a part of the Continent of Europe the willow grouse and the red grouse were one undivided species inhabiting all the north-west of Europe. It is probable, though the experiment would be almost impossible to carry out, that were the eggs of a number of willow grouse now brought to Scotland and hatched on the moors, they would tend to keep apart from the native red grouse, and not inter-breed with them, in which case we should say that the Scotch form is a "species on the make," or, even, a completed and distinct species. On the other hand, it is possible that the two forms would freely pair with another, and that the colour and winter coat of the one (probably that of the Scotch form if the experiment were tried in Scotland) would predominate, and after some generations no trace of the other strain would be observable. CHAPTER X SOME SPECIFIC CHARACTERS