270 Dwicut, The Philadelphia Vireo. fale 
olivaceus, both of which are silky white below at the same age. 
Other specimens in my series show the change of the young into 
autumn plumage, which is acquired, as in Vireo olivaceus, without 
moult of flight-feathers or tail, These remain, although the body- 
feathers begin to be replaced by new ones before the wings and 
tail have attained their full growth. The feathers retained are 
the primaries, their coverts, the secondaries, the tertiaries, and 
the rectrices, — all the rest of the plumage is evanescent and is 
renewed soon after the bird leaves the nest. A bird taken July 
28 has the wings and tail fully grown but the deciduous sheaths 
are still in place at the bases of the quills. The brown upper 
parts are mottled with the bright olive-green autumn feathers 
which have extensively replaced the others on the nape, back and 
rump. The forehead and sides of head show many new feathers. 
A yellow band below in strong contrast to the paler first plumage, 
has developed on the throat and shows faintly on the flanks beyond 
the forking of the inferior feather tract. The new wing-coverts 
(except the primary coverts) are beginning to sprout. A bird 
taken August 4 is farther advanced. The sheaths of the quill 
feathers have disappeared; the wing-coverts are nearly full 
grown; and the new body plumage is nearly complete, only a few 
feathers still in their sheaths sprouting here and there. A bird of 
August 6 is almost entirely in fall dress, and others of August 15 
are still moulting a few auricular and abdominal feathers, while 
one of September 24 shows no trace whatever of the moult and is 
practically indistinguishable from the adult. Still, in average 
specimens the yellow below is a little richer and extends further 
over the abdomen and the bill is yellowish instead of blackish as 
in the adult. 
Whether there is any spring moult in this species I am unable 
to say for I have seen no specimens taken at a time when it might 
be expected to occur, but the state of the plumage in spring birds 
indicates that there is none. The fall plumage of young and old 
is probably worn until the next annual moult, which begins towards 
the end of July. In spring specimens the amount of yellow is 
variable, although paler than in the fall, and the abrasion is not at 
all marked, but this isto be expected in an arboreal species. A 
specimen of July 22 is the earliest one that shows signs of moult. 
