University of Califorma Publications in Zoology [Vol. 21 



just as do the adults. As regards the later stages, I am unable to 

 distinguish any differences between inunatures in first winter plumage 

 and adults a year or more old. As to sexual differences, males average 

 slightly larger than females, but in color and markings there is no 

 discernible variation. Seasonal differences are shown solely as the 

 result of wear and fading of the feathers. There is but one annual 

 molt, after the juvenal stage is passed, occurring in the late summer 

 and including the entire feather covering, with no assumption of a 



Fig. C. Tails of three subspecies of fox sparrow, natural size. 



a. FassereUa iliaca iliaca, adult male; no. 6088, Mus. Vert. Zool. ; Eastford, 

 Connecticut; April 12, 1876. 



b. FassereUa ilkica imaJasclicensis, inunature male; no. 26031, Mus. Vert. Zool.; 

 near Yosemite Point, Yosemite National Park, California; October 30, 1915. 



0. FassereUa iliaca mariposae, adult male ; no. 29089, Mus. Vert. Zool. ; Sisson, 

 Siskiyou County, California; May 15, 1918. 



special breeding dress such as is seen in so many species of birds. 

 Consequentl}', a study of variation in this group is narrowed down 

 quite closely to a consideration of but one category of differences, 

 namely, geographic variation. 



The widely distributed fox sparrow {FassereUa iliaca) is variable 

 to an extreme degree, and many subspecies have accordingly been 

 described from different parts of its range. In the number of recog- 

 nizable local races developed, Passerella iliaca is second only to the 

 song sparrow {Melospiza melodia) and the horned lark {Otocoris 

 alpestris) in North America; the extremes of geographic differentia- 

 tion attained are at least as great as in any other North American 

 bird species. In the genus Passerella the principal lines of variation 

 lie (1) in coloration — ranging from bright reddish browns to clear ^ 



