SPECIES IN THE MAKING 117 



(pronounced "reeper") by the Norwegians. One is the 

 same bird in every respect as the Scotch ptarmigan, and 

 is known as "the mountain rypd." The other is very 

 close to our red grouse, and is called "the common or 

 bush ryp4" 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 ryp^, 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 accord- 

 ingly. 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 im- 

 possible 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. 



