ANMAI. I'KKSISri'.NC'V AM) V.GC. I'UODUCTION 



193 



1. Corrchition I^etxce"n Hdtrhhxi half aud Annual Perslstencii. 



ilic class interval for liatcliiiisi date is seven days, and the class interval for 

 annual persistency is 15 days with a ranfie of from (J7 to 366 days. The fol- 

 liiwin": constants were calculated on 217J) hirds: 



Number of liirds . . . . . 

 -Mean hatching date (April 18) 

 Hatching date standard deviation . 

 Mean annual persistency . . . . 

 Persistency standard deviation 

 Coefficient of correlation .... 

 Regression hatching date on jiersistency 

 Regression persistency on iiatching (hile 



217.9 

 4.28 

 ±2.21. 

 300.i7 

 ±62.64. 

 —.2208 ±.01 37 

 —.008 

 —6.187 



The .ihove constants indicate that, on tlic average, the hirds hiid for 300 

 days l)efore the onset of complete molt. This figure is somewhat lower than 

 it would he if maximum persistency had not been ])laced at 366 days, because 

 some of tiie birds laid for a greater time interval. The standard deviation 

 in persistency amounts to almost 63 days and furnishes statistical evidence 

 of very marked variability in persistency. 



The coefficient of correlation between iiatching date and annual persistency 

 is negative and statistically significant. While this is not an intimate correla- 

 tion, it does demonstrate a tendency for early-hatched birds to lay longer 

 than late-hatched birds. The fact should be kept in mind, however, that the 

 earliest hatch was taken off" each year about March 2.') and that this date 

 should not be considered very early in this latitude. 



2. Correlotiun lietxceen Hcdchinti l)<tfe E-irller than the Men?i nnd Hi()h 

 Persistencfi. 



As previously stated, the birds have been cli\ idcd into two classes with 

 regard to persistency, namely, high and low. All birds are classed as hUjh in 

 persistency when they lay for 315 days or more before molting. Birds laying 

 for a shorter period than 315 days arc classed as low. By dividing the popu- 

 lation of 2179 birds into these two classes for persistency, and by again classi- 

 fying these as hatched earlier or later than the population mean, an absolute 

 measure of the correlation lietween early hatching and high persistency is 

 obtained. The results of this classification follow: 



Hatching Date 



I High Persistency | Low Persistency 



I ' I 



I'.arlier tlian population mean 



720 



458 



Later than popidation mean 



Totals 



416 



1136 



585 



1043 



Coefficient of correlation 



+.3771 ±.0124 



