^^'•,5,V"] Recent Literaiure. 283 



Strong's ' Quantitative Study of Variation in the Smaller North Amer- 

 ican Shrikes.'^ — This is an attempt to employ statistical methods in the 

 study of variation in a group of birds, and to apply the "precise criterion 

 of species " of Davenport to a problem of bird classification. The group 

 of birds chosen for this purpose is the Shrikes of the Lanius ludovicimiits 

 group. The material employed consists of 174 skins, which include only 

 specimens properly available for such a purpose. Specimens showing 

 mutilations or lacking data as to sex have been rejected. 



The characters especially considered are length of wing, length of tail, 

 length of bill, depth of bill, curvature of bill, and color. The methods 

 employed are too abstruse for description in the present connection, 

 and the interested reader is referred to Dr. Strong's paper for a clearer 

 understanding of his manner of procedure. The paper is illustrated by 

 numerous diagrams showing ' frequency polygons ' for all the characters 

 considered. In the quantitative determination of color the Bradley and 

 Milton ' color-top ' was employed, the mechanism and use of which is 

 duly described. He considers that "one of the most important results 

 reached is the determination of the relative variability of different charac- 

 ters in a group of birds representing geographical areas of considerable 

 size." 



Some of his remarks near the close of the paper are worthy of careful 

 consideration. Speaking of the various races of the L. ludoviciajius group, 

 he says : "I believe that migrans is as worthy of recognition as gambelli. 

 Whether it is profitable to encumber nomenclature with the names of 

 these races, based on slight variations, is a question which is worthy of 

 further consideration. 



"The power of discriminating fine shades of color varies in different 

 persons, and it can be highly developed by education. At the present 

 time there is much activity among certain systematists in the production 

 of new subspecies for geographical varieties, which long experience and 

 special adeptness enable them to distinguish. A variation, no matter how 

 slight, that can be correlated with geographical range is considered to 

 warrant an addition to nomenclature; but the discovery and description of 

 geographical races can be carried on almost ad hifinitum.'''' In regard to 

 the use of the method of the 'precise criterion,' he says, he does not 

 argue for its universal use, but believes that it is both " desirable and 

 practicable to employ it in certain problems of taxonomy," such, for 

 instance, as the one he has in hand. While the ordinary work of classifi- 

 cation does not require the precision in treatment furnished by purely 



1 Contributions from the Zoological Laboratory of the Museum of Com- 

 parative Zoology at Harvard College. No. 121. A Quantitative Study of 

 Variation in the Smaller North-American Shrikes. By R. M. Strong. With 

 eight figures. American Naturalist, Vol. XXXV, April, 1901, pp. 271-298. 



