20 THE GROUSE SUBFAMILY 



patches of ground whence food is obtainable, no migration is neces- 

 sary. Where the snow forms but a loose covering, not too deep, the 

 birds, Mr. Millais tells us, will burrow therein for food, while in 

 Norway they often follow the reindeer and dive into the holes made 

 by the deer in scraping up moss with their feet, thereby securing the 

 ice-preserved berries. Save, indeed, when it is abnormally deep, 

 snow has no terrors for them, as is shown by the fact that they roost 

 thereon nightly. At such times they preserve a scattered formation, 

 unlike the grouse and the partridge, which sleep close together. 

 These roosting-holes are easily discovered by the pile of dark drop- 

 pings left therein. Similarly Seebohm 1 remarks of the capercaillie 

 that it "generally roosts in trees, but in severe seasons it will seek 

 shelter from the cold by burrowing into the snow." But there is in 

 these cases no burrowing and tunnelling such as Mr. Chapman has 

 described in the case of the rock ptarmigan. 



If, however, the weather becomes unusually severe, then a general 

 and extensive exodus becomes imperative. Their more extended 

 wanderings however, in Scotland at any rate, are implied rather than 

 observed. And this because such journeys are performed at altitudes 

 too high for observation. But the fact that high mountains known to 

 have been the resort of large numbers of ptarmigan have been 

 found suddenly deserted, while distant mountains under less severe 

 climatic conditions but on which the stock had been reduced to the 

 vanishing point have been found "alive" with birds, leaves little 

 doubt as to the interpretation to be placed on the phenomena. On 

 the Continent, however, and in N. America in the case of the doubt- 

 fully distinct rock-ptarmigan migratory movements on a large scale 

 have been observed, in Labrador extending over several hundred 

 miles. 



In varying degrees, then, capercaillie, blackcock, and red-grouse 

 all migrate to avoid stress of weather, or rather to secure food. And 

 the same is true also of the ptarmigan. But, living in regions where 



1 Seebohm, British Birds, vol. ii. p. 442. 



