18 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Tn all my examples of hypoleweus the entire surface of the plumage which 
covers the under side of the wing is clear, immaculate white. Two birds have 
some concealed slaty or brownish ona very few of the longer coverts lying near 
the edge of the wing, but this is so restricted in extent and situated so near 
the bases of the feathers as to be scarcely noticeable, even when the plumage 
is violently ruffled ; nor can it, I think, be fairly regarded as representing 
any real approach to the conspicuous and practically universal dark mottling 
found on the under wing coverts of B. cravert. 
B. hypoleucus, as represented in my collection, invariably has the whole 
inner web of the first primary pure white to within about an inch and one 
half of the extremity of the feather. Beyond this point the white gradually 
recedes from the shaft, terminating on the inner edge of the feather about three 
quarters of an inch from its tip. The shaft itself, with an exceedingly narrow 
space (a mere hair line) bordering it inwardly, is brownish white. With each 
succeeding quill the white retreats further and further from the tip of the 
feather, at the same time losing something of its purity. Beyond the sixth or at 
most the seventh primary it is rarely appreciable excepting at the extreme bases 
of the feathers. None of my examples of eraverz show well defined white areas 
on any of the quills, although the brown of their primaries is often a shade or 
two lighter on the inner than on the outer web and sometimes changes insen- 
sibly into brownish white near the bases of the feathers. 
Two of Mr. Frazar’s specimens ( # No. 18,288 and 9 No. 18,294), both taken on 
the same date (March 1), are young, about one-half grown and still clothed, for 
the most part, in down. This, over the upper parts, is seal brown, slightly 
redder as well as paler than in adult birds and with fine transverse markings 
of whitish besprinkling the back and rump — but not the crown nor the wings. 
The throat is grayish, the abdomen white. On the jugulum and breast the 
down has been replaced by true feathers — those of the second stage of plu- 
mage and everywhere silky white save on the sides of the breast, where they are 
flecked with minute spots of blackish. The sides of the body with the under 
as well as the upper surfaces of the wings are covered with down of nearly the 
same shade of brown as that of the crown and back, but there are also a few 
budding wing coverts, as well as quills, the expanding tips of which are de- 
cidedly darker in color. 
Other specimens in my series illustrate practically every stage through which 
the young pass in arriving at maturity. They show that the natal down is 
shed first on the breast, next on the throat and abdomen, next on the wings, 
next on the back, next on the chin, next on the center of the crown, next on 
the forehead, last of all on the occiput and sides of the crown. With the dis- 
appearance of the last shreds of down the bird completes what I suppose must 
be called its first winter plumage, although this in specimens which, like mine, 
were hatched and reared in January and February is really assumed in early 
spring. After perfecting this plumage the young can be distinguished from 
their parents only by their shorter and weaker bills, by the darker (nearly dead 
black) coloring of their upper parts and by the presence of numerous fine but 
