62 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 
brown” on the head, neck, and sides, and to “ tilleul buff,” or nearly 
white, on the belly. The molts and plumages seem to be similar to 
those of the common loon. Prof. R. Collett (1894) has made an 
extensive study of the plumages of the yellow-billed loon in Nor- 
way, and the following items are taken from his excellent paper on 
the subject: 
The young of the year are barely full grown the first autumn. One from 
the neighborhood of Tromsé has still a shortish and undeveloped bill. During 
the first autumn the winter plumage is recognizable by the light, somewhat 
sharply defined margins of the feathers of the back. In shape these feathers 
are rounded or almost pointed. The 1-year-old bird (South Varanger, June 
23, 1891) still bears its worn first winter plumage. The light margins of the 
upper surface have become bleached, almost whitish, and partly worn, from 
which the feathers begin to assume the more square-cut edge, which at once 
distinguishes the back of the adult bird from those of younger ones. 
In the autumn and winter of the second year the birds still retain a gray 
plumage, which is, however, easily distinguishable from that of the young ones 
by the color and shape of the back feathers. The light margins on the upper 
parts have been thrown off, and the back, on the whole, has become darker; 
most of the feathers have a lighter grayish-brown patch where the large white 
summer spots will subsequently appear. But these patches are often weakly 
margined and party indistinct. In shape these feathers are somewhat square 
cut, as in all old individuals. The bill has attained its full length and shape, 
and its color is about the same as in individuals in their nuptial plumage. 
The lower neck bar is more or less indicated by the dusky terminal rays on 
the feathers, which are here more dense and darker than on the throat. 
I am inclined to think that the plumage just described is identical 
with, or indistinguishable from, the adult winter plumage; at all 
events, he does not seem to have pointed out any differences which 
might not be accounted for by individual variation. 
He says, further: 
The nuptial plumage is assumed when the individual is at least 2 years old. 
If we may reason by inference from what we know of the molts 
and plumages of the common loon, I should say that young birds might 
be expected to begin assuming the adult nuptial plumage at any time 
during their second winter, from December to February, or when 
18 or 20 months old, the time varying greatly in different individuals. 
The seasonal molts and plumages of the adult are, evidently, prac- 
tically the same as in the common loon. Professor Collett (1894) 
has considerable to say about the transformation of feathers, imply- 
ing a color change without molt or combined with it; but I am in- 
clined to think that no changes take place except by wear or by 
molt. He hardly seems to have proven his case and his following 
statement seems to contradict his claim: 
The recoloration takes place rapidly, probably in the course of a few hours in 
each individual feather, and it is quite exceptional to find feathers in the course 
of transformation. 
