WINTER CYCLE AXD WINTER PAUSE l^]^ 



tion between age at first egg and length of the winter laying cycle. Class 

 intervals of ten days have been used for age, and the respective ages of the 

 individuals tabulated against their winter cycle length. The constants de- 

 termined are as follows: 



Number of birds .... 

 Mean age at first egg . 

 Age at first egg standard deviation 

 Mean length of winter cycle 

 Winter cycle standard deviation . 

 Coefficient of correlation 

 Regression of age on winter cycle 

 Regression of winter cycle on age 



2078 



203.66 

 ±2.5.92 



52.26 

 ±34.23 



—.4.529 ± .0118 



—.343 



—.598 



Age at first egg varies within moderate limits. Since genetically-early 

 and genetically-late birds are concerned, and because environment probably 

 modifies age and sexual maturity, the standard deviation of age is not ex- 

 cessive. 



A significant negative correlation is shown, as might be anticipated from 

 the constants obtained in section 2. Age of sexual maturity may be classi- 

 fied as a characteristic influencing the length of winter cycle as determined 

 by the onset of winter pause. Here is an example of a heritable trait being 

 negatively correlated with duration of winter cjcle. 



(c) Relation of Winter Cycle to E(jg Production. 



A knowledge of the relation of winter cycle length to winter fecundity 

 and annual fecundity is of value for prediction purposes. If any short-time 

 measure of fecundity that is reasonably accurate in predicting winter and 

 annual production is discovered, it will be of much economic import. Proper 

 culling enables the poultrjiuan to raise mean flock production by disposing 

 of mediocre layers. If a relatively short season of trapnesting gives a clue 

 to probable production for the year, such information will greatly assist 

 poultrjTuen. This section considers tiie correlation between length of winter 

 cycle and winter production and length of winter cycle and annual produc- 

 tion. Since the winter cycle length for each bird is tabulated against her 

 egg record, a true measure of degree of correlation is arrived at. 



4. Correlation Between Length of Winter Cycle and Winter Egg Record. 



Both length of winter cycle and winter e^g record are placed in class 

 intervals of ten for the 207S individual pullets studied. The following con- 

 stants were determined: 



Number of birds 2078 



Mean length of winter cycle 52.26 



Winter cycle standard deviation .... ±34.23 



Mean winter production ...... 56.99 



Winter production standard deviation . . . ±23.40 



Coefficient of correlation -)-.6.538 ±.0085 



Regression of winter cycle on production . . . -|-.956 



Regression of production on winter cycle . . . -|-.447 



