378 



THE GROUSE IN HEALTH AND IN DISEASE 



between the amount of infection and the power of combating the same. That is to 

 say. that the nematode infection which would be fatal to the weak bird might 

 conceivably be the normal burden of the strong Grouse ; and that the same bird 

 might carry with ease in autumn — when well nourished and fully feathered — 

 the number of Strongyle worms to which he would succumb in spring when 

 light in weight and short of food. If we realise this theory in its entiret)^ 

 we shall find ourselves on vantage ground, from which the many and apparently 

 contending aspects of " Grouse Disease," and the numerous hypotheses based 

 thereon, can be readily explained. 



T)ieories of 

 ' ' Grouse 

 Disease" 

 (1) Frosted 

 heather. 



CERTAIN THEORIES OF DISEASE HELD BY SPORTSMEN AND FIELD OBSERVERS. 



First Theory. — A very common theory, especially on the west coast of 

 England and Scotland, is that frost is the cause of " Grouse Disease." 

 This theory is usually stated in the form — that "the frost of early 

 spring browns the heather, birds eat the heather and die of 

 indigestion." This is a very good example of an incorrect deduction 

 drawn from properly observed natural phenomena, and of the ease 

 with which secondary causes are confused with primary ones. It 

 is quite incorrect to say that frost in spring is the immediate cause 

 of " Grouse Disease," for the very excellent reason that of nearly 

 two thousand crops examined by the Committee not one single 

 crop has been found to contain a shoot of brown or frost - dried 

 heather. It is, however, correct to say that when frost comes in 

 late spring, or when the cold east winds brown the young shoots, 

 the area of ground on which the birds can feed is reduced, and 

 there may be therefore both a lowering of the Grouse vitality through 

 a shortage of the food-supply, and an increased danger of infection 

 by the Strongyle worm, through the congestion of the birds upon 

 a small area of feeding-ofround. At this season also laro-e areas on 

 some moors begin to show the "burned" and "foxy red" appearance 

 which is caused by the attacks of the heather beetle. The old stick 

 heather, ragged and sparse, is of little use for food. It is only 

 in the thick six- to fifteen-year-old heather that green shoots can 

 be found under the browned tops.' As will be shown later, 

 on a badly-burned moor this may mean a very great curtailment 



' See chap. xix. p. 422. 



