170 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 



white. The eggs are usually heavily spotted or boldly blotched with 

 the darkest shades of brown or black ; also with underlying spots 

 and blotches of variout shades of drab, gray, lilac, or lavender, pro- 

 ducing very pretty eflfe.cts; many eggs are less boldly marked or 

 even finely speckled. The measurements of 51 eggs in the United 

 States National Museum average 60.5 by 41 millimeters; the eggs 

 showing the four extremes measure 68.5 by 41, 64 by 43.5, 57 by 

 39.5, and 60 by 38.5 millimeters. 



Young. — Mr. W. Otto Emerson, in his notes sent to Major Ben- 

 dire, gives the period of incubation as 21 days and- says that both 

 sexes incubate by turns, both of which statements are corroborated 

 by others. He also says that the young are fed principally on small 

 fish and do not leave the nesting site for the water until they are 

 fully fledged. After tlie first few days the young become very 

 lively; they dislike daylight and, if exposed to it, will run away 

 and hide in the remotest crevices; it is very difficult to catch them, 

 much more so to photograph them, among the loose rocks where 

 they live until big enough to fly. It is well that they are so secre- 

 tive in their habits, for they have many enemies and protection is 

 much needed at this critical time for the survival of the species. 



Plwmages. — The young guillemot is hatched with a complete cov- 

 ering of soft, thick down, " fuscous black " above, shading into 

 " clove brown " below. Late in July or early in August the juvenal 

 plumage begins to appear on the sides of the breast. The juvenal 

 plumage is similar to the corresponding plumage in the black guille- 

 mot, but it is usually more dusky both above and below, the dusky 

 markings on the breast sometimes predominating. This plumage is 

 worn through September, when a partial and gradual molt pro- 

 duces the first winter plumage. Young birds in winter are darker 

 than adults, especially on the upper parts, which are almost wholly 

 " fuscous black " without any white edgings ; the throat and breast 

 are mottled with dusky. A partial prenuptial molt in young birds 

 takes place during March, April, and May, at which the black first 

 nuptial plumage is partially acquired; but young birds may still 

 be recognized by the wings, in which the white patches are mottled 

 with black and which are not molted until the following summer. 

 Beginning about the middle of August, a complete postnuptial molt 

 occurs, and by the last of September, when the young bird is between 

 14 and 15 months old, the adult winter plumage is acquired and 

 old and young birds become indistinguishable. 



The adult winter plumage differs from the first winter in being 

 almost wholly white below and in having the scapulars broadly 

 edged with white, the feathers of the back narrowly edged with 

 white and the pure white wing patches. Adults have a prenuptial 

 molt involving all the contour feathers, at which the black plumage 



