No. 412.] SMALLER NORTH-AMERICAN SHRIKES. 287 
The Campestrian subprovince includes arid portions of the 
United States, where paleness of color in the fauna is supposed 
to be correlated with this condition. 
TABLE V.— 22 MALE SHRIKES FROM THE APPALACHIAN 
SUBPROVINCE. 
Classes of Length of Bill in Millimeters. 
Classes of Total. 
Depth of Bill. 
10.6 | 10.9 | 11.2 | 11.5 | 11.8 | 12.1 | 12-4 | 127 | 13. 
8.4 mm I I 
8.6 mm. I I 2 
8.8 mm. I 3 I 5 
9.0 mm. I I 2 I I I I 8 
9.2 mm. I I 2 
9.4 mm. ` I I I 3 
9.6 mm o 
EMEN R I 1 
aa ee s.l] I 6 5 I 4 I I I 22 
While such correlations are frequently suggested by the 
fauna of desert regions, the relations of humidity to color 
are still problems for further investigation. 
Very great variations in the melanism of the upper tail 
coverts are shown in Fig. 8. The shrikes of the Campestrian 
subprovince have here also a mode of little melanism, 30%, 
while a mode of great melanism, 70%, is found for Austrori- 
parian shrikes. The upper tail coverts of Campestrian shrikes, 
especially those from Colorado and Arizona, are very light 
gray. This peculiarity has caused the race to be designated 
as the white-rumped shrikes. 
B. Tables of Constants of Frequency Polygons. 
In Tables VI-XIII will be found indices of variation for all 
the material studied. All computations have been made from 
measurements grouped into classes. This grouping has been 
adopted both in drawing the polygons and in determining the 
indices of variability, in order to reduce the “probable error." 
