172 



TECHNICAL BULLETIN 8 



Mean length of winter cycle is 52.26 days wiiile mean winter production is 

 56.99 eggs. Winter production exceeds the production of the winter laying 

 cycle because most of the pullets resume laying previous to March first 

 following a pause. An arbitrary termination of the winter season at the 

 close of February in all cases does not give a true measure of winter pro- 

 duction and no definite calendar date will suffice. 



The standard deviations of both winter cycle and winter production are 

 excessive. This fact further establishes the variability as due to inheritance 

 and environnient. 



The above constant discloses a very intimate positive correlation be- 

 tween length of winter cycle and winter production. Here is concrete evi- 

 dence establishing an important relation between long winter cycle and high 

 winter egg record. 



The importance of optinmm hatching date, age at first egg, and date of 

 first egg in relation to the length of the winter laying cycle lias been pre- 

 sented in sections I, 2, and 3. Possibilities of shortening the pause period 

 by breeding methods are to be handled in another publication. Probably the 

 most important consideration is the correlation between length of winter 

 cycle and annual egg production, studied in Hie next section. 



f/. Correlation Between Length of M'inter Cycle auil Annual Prodncfion. 



Annual egg record depends upon a vast array of environmental forces 

 and upon a series of Mendelian factors. Specific information concerning 

 many of these influences has never been presented. This section attempts to 

 present in concrete fonn the relation of lengih of winter cycle to annual 

 production over a period of years. On 131 !■ pullets the following constants 

 appear: 



Number of birds 1314 



Mean length of winter cycle 53.52 



Winter cycle standard deviation .... rt34.87 



Mean annual production ...... 172.53 



Annual production standard deviation . . . i!i41.13 



Coefficient of correlation ±.4027 ± .0156 



Regression of winter cycle on production ... -j- 341 



Regression of production on winter cycle . . . 4-.475 



This group of birds averaged slightly under 173 eggs during their pullet 

 laying year of 365 days beginning with their first egg. The standard devia- 

 tion in production illustrates a wide range of fluctuation. The actual r.^nge 

 in annual egg production was from 35 to 275. 



A positive correlation of substantial magnitude exists between winter 

 cycle length and annual egg record. Length of winter cycle, therefore, fur- 

 nishes a rather dependable short time measure of probable annual produc- 

 tion for a population. Winter cycle length is discernable only for pullets 

 exhibiting winter pause. By trapnesting during the first part of the laying- 

 year, it is possible to discover the length of the winter cycle and conse- 

 quently the time of appearance of its complement, the winter pause. 



