382 THE GROUSE IN HEALTH AND IN DISEASE 



cases to a tenth, of its normal size. The migration of birds is a 

 question that has only recently been studied, and some very remark- 

 able facts have been brought out as to the extent and length of 

 time that birds desert the high ground.^ 



Sixth Theory: Corn Theory. — This theory suggests that by eating 

 (6) Feeding ^^™ ^'^ *^® stook birds are seriously aflfected in health, and die of 

 on corn. disease in the year following. 



This is another example of faulty deduction from correctly 

 observed natural phenomena. The fact that birds go oft" 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 the birds 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 misinter 

 pretation 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 Com- 

 mittee, that the immediate cause of "Grouse Disease" among adult Grouse is 

 the Strongyle worm, and that there is an intimate relationship between the power 

 of resistance of the stock and the degree of infection required to aftect the 

 birds injuriously. 



The next question that has to be considered is whether there is any proof 

 that this relationship can be artificially controlled. Can it be shown that more 



birds can be carried on a moor if they are well distributed, and if their 

 measures vitality and weight are raised by an increased supply of food at all 



times of the year ? The answer to this is undoubtedly Yes ! and the 

 four following examples are put forward to show what results have been obtained 

 on well-managed moors. 



' Vide chap. iii. pp. 25 et eeq. 



