4 MASS. EXPERIMENT STATION BULLETIN 423 



Intensity 



4. Relation of Winter Clutch Size to Annual Production 



Winter intensity is one of the most useful tools in selective breeding, as pointed 

 out by Hays (1944). Furthermore, birds lacking genetic high intensity averaged 

 31 fewer eggs in the first laying year than those exhibiting high intensity (Hays, 

 1944a). The coefficient of correlation, as previously reported for the same popula- 

 tion (Hays, 1944), is repeated here with the constants found: 



Number of birds 1470 



Mean winter clutch size — eggs 3.23 



Winter clutch size standard deviation ±1.42 



Mean annual production — eggs 213.57 



Annual production standard deviation ±43.38 



Coefificient of correlation +.5011 ±.0132 



Correlation ratio .5603 



Regression was non-linear and the correlation ratio .5603 shows an intimate 

 association between winter clutch size and annual production. 



5. Relation of Spring Clutch Size to Annual Production 



The mean spring clutch size was calculated for the months of March, April, 

 and May and was tabulated agftinst annual production, giving the following 

 constants: 



Number of birds 1467 



Mean spring clutch size-^eggs 4.04 



Spring clutch size standard deviation ±2.44 



Mean annual production^ — eggs 213.59 



Annual production standard deviation ±43.40 



Coefficient of correlation -|-.4836 ± .0135 



Correlation ratio .6228 



The mean spring clutch was larger and more variable than the winter clutch. 

 This greater size is probably due to more nearly optimum weather conditions in 

 March, April, and May. Regression of production on clutch size was non-linear, 

 so the correlation ratio .6228 expresses the association. This is an intimate 

 association and indicates that spring clutch size is a valuable criterion to use in 

 the selection of yearling breeding females for high intensity. 



6. Relation of Summer Clutch Size to Annual Production 



The mean clutch size was calculated for June, July, and August to represent 

 the summer period. These values were tabulated against the annual egg records, 

 giving the following constants: 



Number of birds 1456 



Mean summer clutch size — eggs 3.06 



Summer clutch size standard deviation ±1.68 



Mean annual production — eggs 214.21 



Annual production standard deviation ±42.95 



Coefficient of correlation +.5629 + .0121 



Correlation ratio .6664 



The mean rate of laying is lower in the summer months than in the winter 

 and decidedly lower than in the spring. The standard deviation in summer 

 clutch size is very large, indicating an extreme variability in the rate of laying. 

 Regression was non-linear and the correlation ratio indicates a very important 

 relationship between the rate of laying in summer and the annual egg production. 



