BREWSTER’S WARBLER. 313 
est the growth of the young of this pair in their slow progress from the nestling 
plumage to the first winter plumage. When first seen, on the 15th of June, 
these young birds were probably not more than two days out of the nest, and 
both Dr. Tyler and myself saw, or thought we saw, a deeper yellow tint on 
their breasts and bellies than we had hitherto seen on young chrysopterae and 
leucobronchiales of the same age; by the 20th of June, however, this yellow 
tinge was much less pronounced, and by the 25th of the month, when the tails 
of the little birds were about three quarters of their full length, the yellow was 
scarcely apparent, the young still wearing the juvenile dress. Dr. Tyler had 
fastened a platinum band on the leg of one of the little birds of this family on 
the 15th of June; we were thus enabled to note the change of color in the same 
individual as the days wore on,—a change doubtless due to the loss of the 
fugacious, veiling, yellow tips of the juvenile feathers. 
On the 27th of June we saw the first signs of the post-juvenile moult in 
the loss of one set of wing-coverts with its yellowish bar. By the first of July 
the contour feathers of the juvenile plumage were being extensively replaced 
by those of the first winter plumage. As in former seasons (1910, 1911) a marked 
difference was apparent in the amount of yellow on the under parts of the dif- 
ferent individuals of the same brood. In at least one of the brood now under 
consideration the yellow tint was very faint and it was clear even at this early 
date that this young one was a leucobronchialis; in other members of this same 
brood the second winter plumage displayed a strong yellow tint on the throat 
and along each side of the breast and belly, following the area of the pteryla 
ventralis and leaving an ash-colored longitudinal band along the median line 
of the abdomen, caused by the retention of some of the juvenile set of feathers. 
As time went on, the yellow color gradually became fainter and restricted for 
the most part to the breast, leaving the throat and abdomen ashy white; the 
growth of a black trans-ocular stripe and yellow wing-coverts now perfected 
the garb of Helminthophila leucobronchialis. On the 12th of July at least two of 
this brood of young birds were as slightly tinged with yellow as the young 
leucobronchialis figured on the plate of my memoir of 1911 (fig. 1). Not one 
of this brood developed the least trace of the black throat and broad cheek- 
pateh of H. chrysoptera. 
As I have previously said, the varying amount of yellow, at the same date, 
in different young Brewster’s Warblers of the same brood was noticeable in 
all of the years in which we observed the growth of the winter plumage in these 
birds. This may be the result of different degrees of precocity in the individ- 
