136 THE GROUSE IN HEALTH AND IN DISEASE 



heather which produces good food during the months of February, March, and 

 April, all the birds upon a moor are forced to concentrate upon small areas 

 Cause of f feedin g g^nd. 1 Consequently, there is a tendency for these small 

 fnfecUon 6 areas to become heavil J infected with the Trichostrongylus even from 

 the droppings of healthy birds. At first there are no evil results, for 

 the eggs take some weeks to go through the necessary stages of metamorphosis 

 before the worms become actively dangerous to the health of the bird. 2 

 Thus, even by the end of February and beginning of March, there is compara- 

 tively little mortality among Grouse. 3 As time goes on, however, the infection 

 becomes more and more intensified, for not only do the larval nematodes 

 assume their most active form, but those which have been eaten by the Grouse 

 at the beginning of the period have had time to grow up and produce eggs in 

 the intestine of their host, and these eggs are in turn distributed over the moor 

 to add to the moor infection. The unhealthy conditions do not result in 

 immediate mortality it has been shown by experiment that birds which have 

 been fatally infected may not die for many weeks. 4 In some cases a severe infest- 

 ment does not result in death. 5 Even in March the mortality has not reached 

 its height, 6 for the majority of birds fatally infected in March will probably 

 not die till April. The infection of the ground continues to increase, and 

 if the same conditions were prolonged for another month or two it is 

 possible that on the majority of moors hardly a bird would survive. Fortun- 

 ately the advent of spring brings a blessed relief to the plague-stricken stock, 

 and with the first appearance of new heather growth at the end of April and 

 beginning of May risk of fresh infection is past. 



Thus it is that in April the infection reaches its climax, but the birds 

 which die in April are probably the result of infection in March, whereas the 

 birds infected in April die in May, even although the conditions have improved. 



This is the explanation of the paradox stated on p. 135. 



It may be assumed that both cocks and hens have the same opportunities 

 for obtaining food, and that the quantity and quality of that food is the 

 Power of same for eacn , consequently each will be equally liable to infection 

 ce - by the Strongyle worm. Why then do the cocks die in larger numbers 

 than the hens 1 Only one answer is possible, and that is, that whereas at this 

 time the power of resistance of the cock is at its lowest, the power of resist- 



' Vide chap, iv p. 81 * Vide chap. x. p. 224. i Vide Chart F, p. 142. 



Vrde, vol. 11. Appendix F. = Ibid. e Vide chart ^ U2 



