106 LIFE HISTORIES OF NORTH AMERICAN DIVING BIRDS 



The composition of the nest depends upon the material at hand. Where 

 spruce trees abound the building materials 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 1st 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 

 gone by December, leaving the bird with pure white under parts; 



