TYPES OF INTENSITY 3 



Character of Birds Used 



All Rhode Island Red pullets hatched during the five hatching seasons of 

 1925 to 1929 are included in these studies if their egg records appeared to be 

 normal. These birds were carried in a number of different projects as follows: 

 non-broody, high fecundity, egg size, variability in production, and intensity in 

 relation to feather pigmentation. The number of individual birds concerned 

 is 1695, except for those reported in Technical Bulletin 11, where the number is 

 2560 in studies concerned with mean winter clutch size. 



In calculating the correlations, the entire range in age at first egg is included, 

 only individuals exhibiting a pause of four days or more are included in the 

 pause population, only individuals going broody during the pullet year are used 

 in the broody studies, and the entire range is included in the persistency studies. 

 All regressions are tested for linearity by Blakeman's (1905) test. Pearson's 

 (1911) correction for the correlation ratio did not significantly alter the size of 

 this constant in these data and is therefore not used. 



A. INTERRELATIONS BETWEEN CLUTCH SIZE 



Whether or not the appearance of high intensity in a bird during a particular 

 period is a good criterion that such a bird is likely to be an intense layer in other 

 periods of the year may be shown best by means of the coefficient of correlation. 

 Consideration will be given to the following relations: Correlation between 

 winter and spring clutch, correlation between winter and summer clutch and 

 correlation between spring and summer clutch. 



1. Correlation Between Winter and Spring Clutch Size. 



The mean winter clutch is obtained by dividing the number of eggs from 

 first pullet egg to the end of February by the number of clutches represented. 

 Mean spring clutch is calculated by dividing the total eggs laid during March, 

 April and May by the number of clutches concerned. Class intervals of one 

 were used, and the mean winter clutch size of each individual was paired against 

 her mean spring clutch. This was done for 1695 individuals to obtain the follow- 

 ing constants: 



Number of birds 1695 



Mean winter clutch 3.35 



Winter clutch standard deviation ± 1.60 



Mean spring clutch 4.07 



Spring clutch standard deviation ±2.21 



Coefficient of correlation -f.3854.+0139 



Correlation ratio .4171 



The above constants show that although the mean spring clutch size was 

 greater than the mean winter clutch size, the standard deviation for spring clutch 

 shows it to be more variable than winter clutch. This fact may be genetically 

 significant since the spring season is the normal period of laying in unimproved 

 stock. 



The regression of spring clutch size vs. winter clutch size is not strictly 

 linear as shown by Blakeman's test. The correlation ratio, therefore, expresses 

 the true relation and amoimts to .4171. Using the squared value of the correla- 

 tion ratio as a criterion of relationship as Ezekicl (1929) has suggested for the 



