/f 6 Brown on Tmmattcrify vs. Tt/dividnal Variation. [January 



IMMATURITY VS. INDIVIDUAL VARIATION. 



BY NATHAN CLIFFORD BROWN. 



Many readers of the Bulletin are doubtless familiar with a 

 phase of plumage of Zonotrichia albicoUis^ occurring in spring, 

 which appears to be the normal dress of this species in imma- 

 turity, indicating, therefore, that its representatives do not attain 

 their finest livery until the second year of their existence. In this 

 plumage the bird appears as follows : The back, wings, and tail 

 are essentially as in most adult specimens. There are black 

 maxillary stripes. The breast is dull gray, lacking the bluish 

 cast seen in high plumage ; it is distinctly sti^eaked. The throat 

 is grayish-white or rather clear gray, either slightly or not at all 

 contrasted with the breast. The yellow before the eye is very 

 limited in extent and of a dull, greenish tint. The superciliary 

 and median coronal stripes are gray mixed with brownish and 

 dusky. Brown rather predominates in the other markings of the 

 head. In the middle of the breast is a dusky spot, much as in 

 Spizella monticola. 



Feeling that all the distinctive features of this attire indicated 

 immaturity, I was surprised, in October of the present year 

 (1883), to procure specimens of Z. albicollls unquestionably in 

 their first year, as proved by careful dissection, clad in a dress 

 practically identical with that of maturest spring birds. The cir- 

 cumstance naturally suggests the existence of two geographical 

 races of this species, but the true explanation appears to be oflered 

 by evidence which I have recently accumulated in two precisely 

 analoo-ous cases, — those of Loxia atnericana and L. leticoptera. 



The announcement that males of the two North American 

 species of Loxia sometimes — nay often — assume their full red- 

 dish dress in the autumn of their first year, will excite the surprise 

 and perhaps the incredulity of ornithologists ; yet, unless osteo- 

 loo-ical data which I have always considered infallible are to go for 

 nothing, they certainly do so, and the greenish and yellowish 

 examples, commonly called immature, simply illustrate remark- 

 able and extreme individual variation. 



