WINTER CYCLE AND WINIKU TAUSK 



I8:i 



Nuiiil)or of birds ...... 



Me.in .iniui.il ))ersisti'iu-y . . . . 



Annual persistency standard de\ iation 

 Mean len<rth of winter pause 

 Winter pause standard deviation 

 Coefficient of correlation .... 



Regression of persistency on winter pause 

 Regression of winter pause on persistency 



1348 



3<)!).0.'J 

 ±. 54.-89 

 32.39 

 ±21.77 

 -i-.l()17 

 +.256 

 -I-.040 



.0182 



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

 \ariahility is rather wide as shown hy its standard deviation. This vari- 

 ability is no doubt due in part to many environn>entaI influences as well as 

 to dit^'erences 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 3G6 is a close approximation of the actual 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, Ihat environ- 

 mental influences completely obscure the genetic phenotj'pes, 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 coeflicient exists between per- 

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

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

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

 small maenitude, however. 



32. Correlation Between Annual Perttislevcy Greater Than the Mean and 

 the Presence of Winter Pause for the Total Population. 



Annual Persistency 



I Pause I Non- Pause 



I I 



Coefficient of correlation 



-f .21.56 It .0139 



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

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

 to lay later in the fall than do non-pause birds Po.ssibly 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 he pronounced, how- 

 ever. 



