106 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 
The composition of the nest depends upon the material at hand. Where 
spruce trees abound the building waterials are largely small twigs; where 
salmonberry, moss, and ferns are in the vicinity these are utilized, and in 
either case are fashioned into a shallow, saucer-shaped nest. The single egg, 
white with obscure lavender spots, is laid in June from the lst to the 15th, 
Newly hatched young were found as early as the 27th, but the greater number 
hatch out during the first week in July. The period of incubation lasts about 
three weeks, as far as can be determined from the data at hand, though it 
must certainly be somewhat more extended when the burrow is poorly drained, 
and the nest a soggy mass. On August 6 several burrows were opened and 
found to be empty, and about the same time the fishermen reported having 
seen young birds, accompanied by one or both parents, some distance out at sea. 
The duty of incubation rests upon both parents, as individuals of either sex 
have been found in the burrows during the day. During this time the mate is 
fishing at sea, and returns shortly before dark, or, more accurately, about 
10 p.m. The day shift now puts to sea to return in the early morning hours, 
Eggs.—The single egg of the rhinoceros auklet much resembles 
the egg of the horned puffin, both in size and shape. The shape is 
usually not far from “ovate,” and the texture of the shell is fairly 
smooth but dull in luster. The color is dull white, often spotless, 
but more often with faint spots of pale lavender, gray, or light 
brown; some eggs are quite heavily spotted with darker brown. 
One egg in the United States National Museum has a faint cloudy 
wreath of pale lavender about the larger end; others have wreaths 
of lavender spots overlaid with spots or scrawls of “tawny olive” 
or other light shades of brown; all of these are very pretty eggs. 
Mr. Dawson (1909) refers to the markings on the egg as “traces. 
of an ancient color pattern, undoubtedly heavy, still persisting in 
faint lines of umber and in subdued shell markings or undertints 
of lavender and lilac,” which he thinks indicate a former habit of 
nesting in the open. The measurements of 39 eggs in various col- 
lections average 68.5 by 46.2 millimeters; the eggs showing the 
four extremes measure 73.5 by 47, 70 by 50, 63.7 by 44.6, and 65 by 
42.6 millimeters. 
Plumages.—The downy young is described by Mr. Ridgway (1887) 
as “uniform sooty grayish brown, very similar to corresponding 
stage of Lunda cirrhata, but rather lighter in color and with more 
slender bill.” The natal down disappears last from the neck, rump, 
and flanks, being replaced by the first winter plumage, the dusky 
feathers of the wings and back appearing first, and then the whitish 
feathers of the breast. 
Young birds in their first autumn may be distinguished from 
winter adults by their much smaller bills and by the entire absence 
of the postocular and rictal plumes. This first winter plumage is worn 
without much modification until late winter or early spring; the dark 
tips of the breast feathers gradually wear away, and are sometimes 
