CHARACTERS CONCERNED IN FECUNDITY 199 



production as -{-.7082 ±.0072. Tlu- siiiiplc correlation between age at first 

 esrg and annual persistency is rei)orted as — .6146±.0090. There appears to 

 be an important relation between age at first egg and persistency, and this 

 may be accurately determined by the partial correlation coefficient where 

 winter 'pau.se, intensity and days broody are made constant. The calculations 

 give — .5956±.0093 as the partial correlation coefficient. This constant in- 

 dicates an important linkage between iieritable factors for early maturity 

 and for higli persistency as has been previously pointed out by Hays (1927). 

 Therefore, by tiie use of breeding females that carry the early maturity 

 factor tliat is linked with the persistency factor, it is entirely possible to com- 

 bine the two desirable traits in the same individual bird. 



J. Length of Winter Pause and Mean Winter Chitch Size. 



The simple correlation between lengtii of winter pause and winter clutch 

 size is — .0674±.0145 (Hays and Sanborn, 1926b). This constant does not 

 suggest a significant relationship. By applying the method of partial correla- 

 tion where age at first egg, total days broody, and annual persistency are 

 made constant, the coefficient of correlation between length of winter pause 

 and winter clutch size is — .0874±. 014.5. This constant is of very small magni- 

 tude and probably indicates no significant linkage between length of pause 

 and winter clutch size. 



6. Length of Winter Pause and Total Days Broody. 



The simple correlation between length of winter pause and total days 

 broody is — .1832±.0243 (Hays and Sanborn, unpublished data). Such a 

 constant would indicate a tendency for intensely broody birds to exhibit 

 shorter winter pause than do less intensely broody individuals. Possibly a 

 short winter pause is compensated for the following summer either by longer 

 liroody periods or by a greater number of broody periods. By means of the 

 partial correlation coefficient the correlation between the two characteristics 

 may be calculated when age at first egg, winter clutch size, and annual per- 

 sistency are made constant. The partial or net correlation between length 

 of pause and total days broody is — .1609±.0245. This constant is statistically 

 significant and indicates a slight tendency for intensely broody birds to pause 

 for short periods in winter. There is apparently no linkage relation betw^een 

 the dominant genes for winter pause duration and the genes that intensify 

 broodiness, but rather a tendency for short winter pause to be associated with 

 a long period of broodiness. 



7. Length of Winter Pause and Annual Persistency. 



The simple correlation between lengtii of winter pause and annual per- 

 sistency is +•1^1'''— -0182. The magnitude of this constant does not warrant 

 the assumption of an important relation between length of pause and annual 

 persistency. 



The partial or net correlation of winter pause and annual persistency, when 

 age at first egg, winter clutch size, and days broody are made constant, gives 

 the true relation of winter pause to persistency. The partial correlation 



