332 THE GROUSE IN HEALTH AND IN DISEASE 



food-supply in April and early May ; lastly, heavy snow followed 

 by floods tends to wash the moor clear of Strongyle larvae ; all 

 these are factors which benefit the moor. 



On the other hand, a hard winter may do incalculable 

 harm if the birds are driven off the hill ground and massed for 

 several weeks on a small area of feeding-ground. The winter 

 storms, especially in the Highlands, drive birds off great tracts 

 of heather land, with the result that when the food is at its 

 shortest the local feeding-area is reduced sometimes to a half, 

 sometimes to a tenth, of its normal size. The migration of 

 Grouse is a question that has only recently been systematically 

 studied, and some remarkable facts have been brought out as to 

 the length of time for which birds may desert the high ground. 1 



Sixth Theory : Corn Theory. This theory suggests that by 

 eating corn in the stook birds are seriously affected in health, 

 and die of disease in the year following. 



This is another example of faulty deduction from correctly 

 observed natural phenomena. The fact that birds go off the 

 moor in October to eat corn on the low ground usually means 

 that there is not a sufficient natural food-supply on the moor. 



If the birds are short of food in autumn and early winter 

 it is quite certain that they will be still shorter of food in the 

 spring when the carrying capacity of the moor is at its lowest, 

 and it is easy to see how they will in consequence become liable 

 to the hurtful influences of the Strongyle worm. 



It is not necessary to go into any of the other theories of 

 " Grouse Disease " examined by the Committee. The majority 

 appear to be based on a misinterpretation of natural phenomena, 

 and in most cases confusion has resulted from mistaking the 

 predisposing conditions for the immediate causes. All the 

 theories on the subject fall into line with the solution put forward 

 by the Committee, that the immediate cause of " Grouse 

 Disease " among adult Grouse is the Strongyle worm. 



1 Vide chap. i. pp. 28 et seq. 



