MASS. EXPERIMENT STATION BULLETIN 329 



flock. The following constants were determined: 



Number of birds .... 

 Mean winter weight, pounds 

 Weight standard deviation, pounds 

 Mean pause duration, days . 

 Pause standard deviation, days . 

 Coefficient of correlation 



+ 



322 



6.11 



+ .64 



35.24 



±22.98 



0731+ .0374 



The mean winter weight for the pause group was 6.11 pounds and for the 

 nonpause group 5.97 pounds. Evidently body weight was not a factor con- 

 tributing to winter pause because the mean weight was essentially the same for 

 the two groups. The variability in body weight within the pause population 

 cannot be considered high. 



Regression of pause duration on body weight was found to be strictly linear. 

 The coefficient of correlation, however, is of insignificant value, indicating that 

 pause duration was independent of winter body weight. 



11. Character of Pause Duration 



Figure 1 presents the frequency distribution of the pause population with 

 respect to duration of winter pause. The fact should be noted that the 693 

 birds included make up 68.9 percent of the flocks studied. The graph does not 

 depict a normal frequency distribution, because the modal class is made up 

 of birds with the shortest pauses (between 4 and 13 days). It is probable 

 that these short pauses are not due to the same causes as are the longer pauses. 

 By considering only pauses of seven or more days in length it would be possible 

 to closely approach a normal frequency distribution. It is probable, also, that 

 the classification of birds with respect to the presence or absence of winter 

 pause would be more accurate on the seven-day basis, as Hays (1924) pointed 

 out. 



175 



i so 



^ '00 



kl 



f 75 

 50 

 25 



8 



18 28 38 48 58 68 78 88 98 108 118 



PAUSE DAYS 

 Figure 1. Frequency Distribution in Pause Duration. 

 693 Birds — 1933 and 1934. 



