THE WEIGHT OF GROUSE 141 



(c) Moult, in the male taking most effect in March and in September ; 

 in the female in July and November ; probably always leads to 

 some loss of weight in either sex. 



{d) Courtship, in the male always apparently a cause of loss of weight: 

 in the female, owing to increased rest, with some change in 

 the general metabolism and extra opportunities for feeding 

 prior to incubation, seems to lead normally to a very considerable 

 increase of weight. 



(f) Egg laying and incubation, gradually lead to a loss of weight, 

 which becomes more marked when the hen has had the care of 

 a family of chicks. These cares, notwithstanding the abundance 

 of summer food, often result in producing the lowest possible 

 weights in hens, such loss of weight being in some cases due to 

 an attempt to rear a second brood. 



During the hen's incubation the cock somewhat recovers 

 his weight, possibly because the food supply is rapidly improving, 

 and because his energies are not so exhausted by courtship. 



(/) A shortage of good food in a bad winter must often be responsible 

 for a great reduction of weight, and indirectly for an increase 

 of the mortality in both sexes due to Strongylosis in the spring. 

 Similarly the abundance of food in summer, autumn, and early 

 winter must serve to counteract some of the other causes of 

 loss of weight. 

 II. In Disease. 



{a) Strongylosis in both sexes and at all ages leads to excessive loss 

 of weight, and ultimatel}'^ to death, but the maximum incidence 

 of infection is strictly seasonal, accounting wholly for the fact that 

 both sexes die in April and May in very much greater numbers 

 than in any other mouths of the year. The observation that 

 so many more cocks die than hens has been explained largely 

 by the fact that the average power of resistance of the normal 

 hen Grouse is at its best in April and in May ; while that of 

 the normal cock has just been at its worst. 



Another factor which bears on this question is shown by refer- 

 ence to Chart F, p. 142, which shows the average monthly weight of 

 cocks and hens found sick but alive and found dead of Strongylosis 



