272 THE AMERICAN NATURALIST. [Vor. XXXV. 
Criterion of Species " of Davenport ('98) to a problem in bird 
classification. The smaller American shrikes of the genus 
Lanius appeared to me to offer favorable material for the appli- 
cation of quantitative methods to the solution of an interesting 
taxonomic problem. 
The shrikes are a group of passerine birds more or less 
generally distributed in northern Europe and North America, 
and probably of circumboreal origin. The large northern 
shrike, Lanius borealis Vieill., of North America grades into 
the great gray shrike, Z. excubitor Linn., of Europe; and it 
exhibits a strong tendency towards individual variation. 
In the United States, Mexico, and southern Canada the 
breeding! shrikes are not essentially different from the 
northern shrike, Z. dorealis, in certain of its color phases, 
except for smaller size and the more or less complete dis- 
appearance of a conspicuous barring or mottling of the 
breast in adults. This barring of the breast is persistent in 
most adults of Z. borealis and characteristic of the juvenile 
plumage of the southern shrikes, a fact of much phyloge- 
netic interest. 
According to the nomenclature of the American Ornitholo- 
gists’ Union there are at present recognized three races or 
subspecies of the southern or smaller shrikes, which are as 
follows : Lanius ludovicianus ludovicianus Linn., L. ludovicianus 
excubitorides Swains. and L. ludovicianus gambelli Ridgw. 
Subspecies gaméelli includes the shrikes of California and 
vicinity. The shrikes of the rest of the country are classed as 
either ludovicianus or excubitorides, the former being typical 
in the south central states and the latter in the vicinity of 
Colorado. 
The shrikes of New England and the north central states 
have been variously classed, by different systematists, as either 
ludovicianus or excubitorides. Palmer (98) has proposed for 
the shrikes of this intermediate region a new subspecies, 
migrans, whose validity, I believe, can be well tested by the 
* Precise Criterion " method. 
! In this paper the breeding range only is considered in discussing geographi- 
cal distribution. 
