132 THE GROUSE IN HEALTH AND IN DISEASE 



of the year, while the cock is not at his best. There is, therefore, at this 

 season, a tendency for the average weight of both sexes to approximate, and 

 even for the advantage to be on the side of the hen. The diiference in the 

 fluctuations of weight between the cock and the hen bird is shown in the 

 Tables A, B, and C, p. 131. 



The immediate reason for this difi'erence in spring is probably the one which 

 naturally suggests itself; viz., that the exigencies of courtship have a precisely 

 opposite effect upon the male and female. 



In December, the adult cock Grouse's weight averages 24 •22 ounces, compared 

 to 21 '07 ounces for the hen, while in January it is 23"58 ounces compared to the 

 hen's 21 '52 ounces. These may be considered normal averages, the difference 

 at this time of year being dependent wholly upon a sexual difi'erence of size and 

 build, body and bone. In other words, when the birds are all living under 

 healthy conditions, and when the sexual instincts are in abeyance, the hen 

 being less in all her measurements than the cock has a weight correspondingly 

 less by 2 or 3 ounces. 



It is, therefore, essential that average weights, to be of use in making 

 a prognosis or a diagnosis of disease, should include the sexes separately ; 

 and also if the weights be taken in August, September, and October that 

 every bird taken for an average be adult. 



As winter proceeds, we may assume that, unless the weather is unusually 

 open, food becomes less abundant, or, at any rate, less easily obtained and 

 Winter ^^^^ nutritious ; " the sap goes out of the heather," as it is generally 

 feeding. expressed, and there is a large proportion of dry, dark, woody, 

 weather-bitten shoots. 



Data are elsewhere given to prove that the quantity of such food, both 

 by weight and bulk, found in the crops of full-fed birds in winter, is much 

 in excess of what is usually found in the crops of similar birds in summer. 

 In winter, the crops of Grouse often contain five times as much food-stufi" 

 as they ever contain in summer.^ And, although several factors are at work 

 to produce this difi'erence, one of the most important is the necessity of eating 

 a greater bulk of winter heather in order to arrive at the same total of food 

 value in the end. 



Calluna heather is eaten almost exclusively throughout the winter ; though 

 Blaeberry stalks and Blaeberry leaf-buds often replace heather, where they 



' Vide chap. iv. p. 79. 



