THE WEIGHT OF GEOUSE 135 



worth noticing in the case of the hens (see Table B). This argument is borne 

 out by the almost equally sudden rise as soon as the mating is over. 



The post-nuptial moult in the male takes place in April and May. It is 

 complete in June, therefore any loss of weight in the re^alacing of new feathers 

 would make itself felt in the earlier of these three months. From April to 

 August the food supply is improving daily, and the weight of the cock Grouse 

 gradually increases. And it is by no means easy to see why there should be 

 a sudden drop in September unless it is due to the complete (male) moult to 

 the winter plumage. As there is no corresponding drop in the hen, and, as 

 we know, no similar moult, we are probably right in thus attributing for the 

 September fall in the weight of the male to this autumn moult.^ 



It is, however, true that although healthy Grouse are at a much lower ebb, 

 as evidenced by their average weight, during certain months of the Relation 

 year than during others. Strongylosis does not necessarily kill them diseaseTnd 

 off" at these seasons. It kills off the hens when they ought to be '^^'gi^t- 

 at their flood tide of health and vitality ; and the cocks when they ought to 

 be on a good rising average tide. 



We have thus a paradox which may be stated in the following way : — 



More hens die of Strongylosis during April and May than in any other month 

 of the year, notwithstanding the fact that the healthy hen is then at her best 

 so far as weight, fat, and plumage go. 



More cocks die of Strongylosis during April and May than in any other month 

 of the year, notwithstanding that the healthy cock is then already recovering the 

 weight which he lost during courtship, and is at a fair average and rising weight. 



And although one might expect cock birds to die in March and September, 

 when the average weight is at its lowest, this does not occur. 



And whereas one might expect hen birds to die in June and July, or 

 in November, when the average weight in health is at its lowest, this also 

 does not occur. 



In attempting to explain this paradox, it is necessary to recapitulate shortly 

 the conditions which lead to an over-infection of the Grouse with the young 

 Irichostrongylns. 



Elsewhere it has been pointed out that, owing to the small proportion of 



1 The cock Grouse normally moults twice a year, first between April and June, and secondly hetween 

 August and November. The normal hen Grouse al.so moults twice a year, first between February and 

 Ai)ril, and secondly during July and August. 



