96 Dwight, Plumage Wear and Subspecies. f Jan. 



phalcena), for in examining a series of over 200 Sparrow Hawks I 

 have found an unusual number in the midst of moult, making 

 accurate comparisons of old and new plumages possible. On 

 comparing newly-moulted specimens from eastern North America, 

 from the Mississippi Valley, from the Rocky Mountains, from 

 British Columbia, from California, and from Arizona, I find that 

 the fresh plumage of birds from all of these widely differing 

 regions is identical. This is true not only of adults but of young 

 birds in all plumages. Under these circumstances it is only 

 possible to conclude that Sparrow Hawks after a moult fade into 

 pale phalcena in a dry climate, remaining darker wherever the 

 atmosphere is more humid. Furthermore, it is significant that 

 during the breeding season when phalcena is perhaps most typical, 

 the humidity of the air at Denver, we will say, is below 50% 

 while in Boston or New York the average is above 70%. Similar 

 conditions prevail at the time of the prenuptial moult, for the fresh 

 plumage of the Arizona bird is as dark as that of the Eastern, and 

 only fades on exposure to the hot dry air of the Southwest. As 

 phahena therefore possesses no intrinsic character, it should not 

 possess a name. The plumage is sunburnt, but there is none of 

 the incipient variation of which races are thought to be the 

 exponent. It is perhaps fortunate that the describer of phalcena 

 did not name the other "regional phases" that he was able to dis- 

 tinguish. What is true of the Sparrow Hawk is undoubtedly true 

 of other species, but it is far easier to describe a race than it is to 

 produce evidence that invalidates it, and easier still to confuse 

 wear with subspecific characters. 



Most writers have concerned themselves with the effect of 

 climate on the species, not its effect upon the individual. Mr. 

 Grinnell, however, has discussed the effect of wear upon several 

 California species (Auk, 1902, pp. 128-13 1). He states that a 

 race of the Russet-backed Thrush known as osdica does not in 

 early summer differ from typical ustulata taken in Sitka, Alaska, 

 but later in the season fades in the drier, brighter atmosphere of 

 California. This is unquestionably true, and I have satisfied 

 myself of the fact by the examination of numerous specimens. It 

 is desirable, however, to compare fresh plumages ; still, in the 

 case of this Thrush, unless the new plumage is alike in both forms 



