210 BIOLOGICAL LECTURES. 



their more unfortunate companions. It will be convenient 

 for us to arrange our material in the form of tests, as follows. 



Test I : Sex. It will be noted by reference to the tables that 

 of the surviving birds the males are much more numerous than 

 the females. Of the former there are fifty-one (thirty-five adults 

 and sixteen young), while of the latter there are only twenty- 

 one. Among the birds which perished, the females are abso- 

 lutely and relatively more numerous than they are among the 

 birds which survived, although more than one-half (thirty-six 

 out of sixty-four) of the unfortunate birds are males. Of course 

 it may be that male birds are naturally more abundant than 

 females, but the present question is not one of distribution of 

 sex, but rather of distribution of fitness, and the inference is that 

 the females are less competent to resist severe winter weather 

 than are the males, for, while only 28^ of the survivors are 

 females, they constitute 43^ of those that perished. 



Test 2 : Length. The first column of figures on the several 

 tables gives, in millimeters, the lengths of the birds from the 

 tip of the beak to the tip of the tail. An examination of the 

 averages, printed at the bottom of each column, will prove par- 

 ticularly instructive. It will be noted on Tables I and I a that 

 the average length of the adult males which survived (159 mm.) 

 is really less than that of the adult males which perished 

 (162 mm.). 1 Similar figures, 159 mm. and 162 mm. on Tables 

 II and II a , indicate the same relative lengths of the young 

 males of the two groups. The average lengths of the females 

 of the two groups, 157 mm. and 158 mm., Tables III and III a , 

 also indicate an excess in the average length of the birds 

 which perished. The birds which perished, then, males or 

 females, adult or young, are longer than those which endured, 

 and we are justified in concluding that when nature selects, 

 through the agency of winter storms of this particular kind of 

 severity, those sparrows which are relatively short stand a 

 better chance of surviving. 



Test J : Alar Extent. Averages based on measurements 

 from tip to tip of the extended wings fail to bring out any 



1 The numbers printed in light type, both in the text and in the tables, refer to 

 birds which survived ; those printed in heavy type refer to birds which perished. 



