WINTER CYCLE AND WINTER PAUSE 



183 



Number of birds 



Mean annual persistency 



Annual persistency standard deviation 



Mean length of winter pause 



Winter pause standard deviation 



Coefficient of correlation 



Regression of persistency on winter pause 



Regression of winter pause on persistency 



1348 

 309.03 



±54.89 

 32.39 



±21.77 

 -f-.1017 

 +.2-56 

 -^.040 



.0182 



Mean annual persistency closely approaches ten months, but the range of 

 variability is rather wide as shown by its standard deviation. This vari- 

 ability is no doubt due in part to many environmental influences as well as 

 to differences in the inherited capacities of the birds. Only about five per 

 cent of the population fall below 200 days in persistency so that the range 

 200 to 366 is a close approximation of the actu.il range. A study of fre- 

 quency distribution for persistency does not reveal a bimodal curve as might 

 be expected for a population made up of genetically early and late molting 

 birds. Such information suggests two possibilities, namely, that environ- 

 mental influences completely obscure the genetic phenotypes, or else that 

 high persistency is not inherited in simple Mendelian fashion. The mode of 

 inheritance of persistency is out of the scope of this report. 



A small but significant positive correlation coefficient exists between per- 

 sistency and winter pause duration. Thus there is a very slight tendency for 

 birds with long winter pause to lay later in the fall than do short pause 

 birds. Relatively little significance should be attached to a constant of such 

 small masnitude, however. 



£2. Correlation Between Annual Persistency Greater Than the Mean and 

 the Presence of Winter Pause for the Total Population. 



Coefficient of correlation 



+.21.56 ± .0139 



A moderate degree of correlation is shown between the presence of winter 

 pause and high persistency. There is thus a slight tendency for pause birds 

 to lay later in the fall than do non-pause birds Possibly the functional abil- 

 ity of the reproductive organs is somewhat extended by a period of non- 

 production in winter. The relation does not appear to be pronounced, how- 

 ever. 



