134 BULLETIN 130, UNITED STATES NATIONAL MUSEUM 



them a darker appearance. The measurements of 71 eggs, in various 

 collections, average 65.3 by 45.7 millimeters; the eggs showing the 

 four extremes measure 72.5 by 47, 68.5 by 49, 55.4 by 37.7, and 58.9 

 by 35.7 millimeters. 



Plumages. — The downy young of the white-winged scoter is thickly 

 covered with soft, silky down. The upper parts, including the 

 upper half of the head, down to the base of the lower mandible and 

 a space below the eye, are uniform " clove brown," shading off to 

 " hair brown " on the flanks and into a broad collar of " hair brown " 

 which encircles the lower neck. The chin and throat are pure white, 

 which shades off to grayish white on the lower cheeks and the sides 

 of the neck. The under parts are silvery white, and there is an in- 

 distinct, tiny white spot under the eye. The feather outline at the 

 base of the bill is much like that of older birds. Doctor Dwight 

 (1914) mentions a "white patch of down, foreshadowing the white 

 wing patch," but I can find no trace of it in my one specimen. 



In the Juvenal plumage the sexes are alike, dark brown above, 

 lighter and more mottled brown below; there are conspicuous whit- 

 ish patches on the lores and on the auriculars, varying in intensity 

 and extent; the white secondaries, forming the speculum, are tipped 

 with dusky, which often invades much of the inner web. This 

 plumage is often worn without much change all through the winter 

 and into the spring. But usually in December, or a little later, the 

 sexes begin to differentiate by the growth of black feathers in the 

 male and brown feathers in the female, starting in the head, obliter- 

 ating the whitish head patches, and spreading to the back, scapulars, 

 and flanks, the latter being dark brown in both sexes. The bill in 

 the young male now begins to show color, about as in the adult 

 female, but not the swollen shape of the older male. 



A complete post ju venal molt takes place during the next summer, 

 July, August, and September, at which the black plumage of the 

 male is assumed, with the white eye patches and the pure white sec- 

 ondaries ; the flanks are still dark brown in this and in all subsequent 

 plumages that I have seen; the bill now becomes highly colored and 

 approaches the adult bill in shape. The bird is now practically 

 adult, at an age of 14 or 15 months, but the full development of the 

 bill and highest stage of plumage will not be perfected for about 

 a year more. The iris, which is brown in young birds, becomes 

 white at this age. The female also assumes a practically adult 

 plumage, at this molt, which is uniform dark brown; and she will 

 be ready to breed the following spring. 



Adult birds have an incomplete prenuptial molt in early spring, 

 involving the head and body plumage and tail, and a complete post- 

 nuptial molt in late summer, at which time they become incapable 

 of flight. There is no real eclipse plumage, but the appearance of 



