BRITAIN'S BIRDS AND THEIR NESTS. 109 



In general and nesting habits the Ptarmigan resembles 

 its congener. The eggs are laid a month or so later, 

 and are lighter in colour and less densely spotted. The 

 chicks are similar, but of a more chestnut tint. 



In Scotland the Ptarmigan is shot at the same season 

 and in the same manner as the Red-Grouse, and it is 

 also liable to the grouse-disease. 



It is as regards its plumage that the Ptarmigan is 

 most interesting. We may safely say that it presents 

 one of the finest examples of * protective coloration " ; for 

 each season it has a garb perfectly suited to its natural 

 surroundings. It reaps the full advantage of this by its 

 habit of sitting exceedingly closely, and trusting almost 

 entirely to concealment to escape its enemies. Thus the 

 traveller in the mountains may find himself in the very 

 middle of a flock before he is aware of it. On their 

 nests, too, in summer, the birds may usually be very 

 closely approached without their rising. At times, between 

 seasons as it were, they may suddenly find themselves 

 brown specks on a white landscape. Then they become 

 exceedingly wary and difficult to approach, which is an 

 interesting point in the discussion as to what actual 

 knowledge and appreciation of the value of their colora- 

 tion the birds themselves possess. 



This plumage-change of the Ptarmigan and the Willow- 

 Grouse has its analogy in the variations of the Mountain 

 Hare, the Stoat or Ermine among our own mammals, and 

 the Arctic Fox. These, however, frequently assume no white 

 coat in winter in the more southern portions of their 

 range. Experiments, too, have been made with regard 

 to the direct influence of various conditions on the 

 assumption of winter plumage in certain birds ; but the 

 problem is not yet solved. 



In addition to the birds and mammals we have already 



