LENGTH OF BIOI.OCICAL LAVIXC; YEAR 3 



cases where the diflerence between the squared values of the correlation ratio and 

 the correlation coefficient was less than three times its probable error, the relation 

 was considered linear and the correlation coefficient alone is reported. When 

 the regression was non-linear, the correlation ratio is used as the measure of associa- 

 tion. Onh' pullet-year reconls are inckuled in the correlation tables. 



1. Relation Between Age at First Egg a)id Length of Biological Year. 



The correlation between age at first egg and annual persistency in earlier flocks 

 was reported as— .6146+ .0090 (Hays and Sanborn, 1926.) In such cases persistency 

 is terminated within 365 days from the date of the first pullet egg. Now the 

 question arises whether the earlier maturing birds are also more likely than the 

 later maturing birds to continue to lay after the termination of the 365-day period. 



Records are available on 911 individuals upon which the correlation between 

 age at first egg and length of biological year was calculated. 



Number of birds 911 



Mean age at first egg — days 190.47 



Age standard deviation + 21.32 



Mean biological year — days. 363.62 



Biological year standard deviation +43.16 



Coefficient of correlation -.5661 +.0152 



The mean length of the biological year is very close to 365 days. The range for 

 this character was from 80 to 4<S4 days. The standard deviation amounts to 

 11.87 per cent of the mean, which should not be considered large in view of the 

 combined effects of environment and heredity. 



The relation between age at first egg and duration of biological year is linear by 

 Blakeman's test and is therefore measured by the coefficient of correlation. The 

 squared value of this constant is. 3 193, indicating that about 32 percent of the vari- 

 ation in duration of the biological year is due to variation in age at first egg. The 

 correlation table also shows that almost 50 per cent of the birds studied had a 

 biological year equal to or greater than 365 days. The correlation coefficient 

 reported here does not differ greatly from that reported by Hays and Sanborn 

 (1926) as the measure of the relation between age at sexual maturity and persis- 

 tency within the 365-day laying year, namely -.6146 + . 0090. The data indicate 

 that earh- se.xual maturity- is rather intimately associated with a long laying year. 



2. Reliition Between Winter Pause Duration and Length of Biological Year. 



Winter pause marks a period of non-productivity between the date of the first 

 pullet egg and March 1. The duration of the pause varied from 4 to 113 days 

 in the population studied. Only those birds having a winter pause of 4 days or 

 more are considered in this section. If the winter pause represents a period of 

 recovery for the reproductive system, there may be some relation between pause 

 duration and the duration of the biological year. A total of 494 pause birds are 

 available in the population studied. These were tabulated in a correlation table 

 and the following constants derived : 



Number of birds 494 



Mean winter pause — days 21 .03 



Winter pause standard deviation +15.19 



Mean biological year — days 365.84 



Biological year standard deviation 41.37 



Coefficient of correlation +.1744 +.0294 



