No.412.] SMALLER NORTH-AMERICAN SHRIKES. 281 
IV. RESULTS. 
A. Indices of Variability. 
1. Wing and Tail.— In Figs. 4-8, frequency polygons based 
on measurements of various dimensions, the position of the mean 
class is indicated by a heavy verticalline. In Fig. 4 are given 
frequency polygons for the lengths of the wing (4 A) and tail (4 B) 
of all available male shrikes. They show a striking absence of 
variability for these characters in a series of individuals repre- 
senting four subprovinces with greatly varying conditions. 
In Tables I-III are given correlations between the length of 
wing and the length of tail. I have used the method of 
Duncker (Davenport, '99, p. 33) in determining coefficients 
of correlation. The “probable error" has also been deter- 
mined by the following formula (Davenport, '99, p. 34), in 
which p is the coefficient of correlation. 
0.6745 (1 — p?) 
Van (1 +p) 
On comparing Tables II and III, we find that Florida shrikes 
have a greater length of tail in relation to the length of wing 
than shrikes from the Appalachian subprovince. 
The correlation in these characters for the series from the 
Appalachian subprovince is seen to be 0.157— greater than 
that of the Florida series. This difference is possibly due in 
part to the skewness of the curves of frequency for these series, 
Which renders precise correlations difficult. 
POE qt 
TABLE I.— 140 MALE SHRIKES FROM THE ENTIRE REGION. 
Mean of wing = 99.06 + mm. Mean of tail = 101.571 + mm. 
91 = e = 3.48 3 
= 2.74 + mm. 2 mm. 
i WING, SUBJECT. TArL, RELATIVE. 
: —7—5-—3 ~i o 2 4 8 
Rel. class 100 | roz 104. 106 108 110 mm. 
Sub. class (I) 94 96 95 . 4 (II) 
Xi 
Doe =i 473 4 
96mm. — 3 2 4. 5 3 3 I 
98 mm I |! 4 9 wl HH 6 4 
100 mm. o I 6 7 6 2 
102 mm. 2 : ? 6 3 2 
mm. a I 5 3 
106 mm. (III)6 . 2 I (IV.) 
p = 0.5688 + P. E. p= + 0.038 + 
