"GROUSE DISEASE " COCCIDIOSIS 



263 



The principal known sources of coccidian infection are : Sources of 

 (i.) Cysts may remain on the moors from previous out- infection. 

 breaks, and retain their infectivity till the next 

 season. 



(ii.) Some birds may largely recover from an early 

 attack of Coccidiosis but become chronics, harbour- 

 ing oocysts and thus acting as reservoirs and 

 carriers of infection. 



In view of the fact that the commonest cause of outbreaks Overcrow* 

 of Strongylosis is the congestion of a large number of Grouse m ^' 

 upon a smaller area of moor than can carry them with safety, 

 it was only natural that the Committee should suspect that 

 overcrowding might similarly be a contributory cause of Coc- 

 cidiosis. The reports seem to support this view, for of fourteen 

 moors which had high mortality among chicks, no fewer than 

 eleven were reported as having more than an average stock 

 left over from 1910. Of thirty-five moors where the mortality 

 among chicks was slight, twelve were reported as heavily 

 stocked, four as lightly stocked. Of seventy-one moors where 

 no mortality among chicks was observed, twenty-seven were 

 heavily stocked, eleven were lightly stocked, and thirty-three 

 carried an average stock. For comparison the results of the 

 reports may be arranged in tabular form as follows : 



TABLE SHOWING PERCENTAGE OF MORTALITY AMONG GROUSE CHICKS DURING 

 THE SUMMER OF 1911, IN RELATION TO STOCK LEFT' OVER FROM 1910. 



