TYPES OF INTENSITY 5 



Number of birds 1682 



Mean spring clutch 4.08 



Spring clutch standard deviation +2.21 



Mean summer clutch 3.04 



Summer clutch standard deviation ±1.60 



Coefficient of correlation +.4593 + .0130 



Summer clutch shows the same coefficient of variation as spring clutch — 

 about 53 per cent, compared with about 48 per cent for winter clutch. The fact 

 should be observed, however, that the actual range in clutch size is ±1.60 both 

 during the winter and summer periods and ±2.21 during the spring season. 



Regression of summer clutch size on spring clutch size is linear by Blakeman's 

 test. The magnitude of the correlation coefficient is greater than those shown 

 in sections 1 and 2. Squaring r, the value .2110 appears which means that 21 

 per cent of the variance in summer clutch size is associated with variance in spring 

 clutch size. 



The data in sections 1, 2 and 3 on the inter-relationships of clutch size during 

 the winter, spring and sunnner periods show significant correlations, yet the 

 correlation is in no case sufficiently intimate to justify the use of clutch size in 

 any one period as an accurate measure of intensity for the year. Hurst (1921 

 loc. cit.) made use of intensity throughout the year in his study of the genetics 

 of egg production, and Hays and Sanborn (1927, loc. cit.) state that annual 

 intensity should be adequately stressed in breeding for fecundity. 



B. SHORT-TIME MEASURES OF INTENSITY IN RELATION TO 

 FECUNDITY TRAITS 



Table 1 is presented to set forth the correlation between six short-time 

 measures of intensity and four characteristics affecting annual egg production 

 and the correlation between each measure and annual egg record. 



Winter Clutch Size 



The coefficient of correlation between mean winter clutch and age at first 

 egg is -.2273 ± .0103. Regression of winter clutch size on age at first egg is strictly 

 non-linear according to Blakeman's test. Therefore, the correlation ratio of 

 .7475 expresses the true relation between these two characters. Squaring the 

 constant .7475 gives .5588 which indicates that about 56 per cent of the variance 

 in winter clutch size is due to variance in age at sexual maturity. In other words, 

 the data show that early sexual maturity is intimately associated with large win- 

 ter clutch size. 



Winter clutch size shows a non-linear relation to length of winter pause. 

 The correlation ratio shows, however, that the two are actually correlated. The 

 constant is .1297 indicating by its squared value of .0168 that about 2 per cent 

 of the variability in winter clutch size is due to variability in pause duration. 



The degree of broodiness measured by the number of days spent without 

 production while broody during the pullet year is associated with large winter 

 clutch size. There is a positive correlation constant of .2205 ±.0186. The re- 

 gression is non-linear and the correlation ratio is .2548. Hays and Sanborn (1927 

 loc. cit.) have already shown that the mean winter clutch size is greater in broody 

 than in non-broody birds. 



