LIFE HISTOEIES OF NORTH AMERICAN PETRELS AND PELICANS. 195 



form, according to Doctor Fisher (1906). The ground color is very 

 pale blue or bluish white, but the egg is generally completely covered 

 with a thick coating of calcareous deposit which is dull white in color 

 and often much nest stained; the surface is smooth and soft; the 

 coating is easily scraped off, showing the bluish tint beneath it. 



The measurements of 41 eggs, in various collections, average 67 by 

 46 millimeters; the eggs showing the four extremes measure 77 by 

 47, 65.2 by 48.5, and 60 by 40 millimeters. 



Young. — Both sexes incubate, and while one is sitting the other 

 often stands on guard nearby. They are exceedingly tame or stupid, 

 merely hissing at the intruder when approached. Doctor Fisher 

 (1906) says: 



It is a curious fact tliat altliough there are two eggs, only one young is reared. 

 Often all signs of the second egg were removed, as if the young had hatched and 

 had been devoured by a parent or some marauding Fregata. But more fre- 

 quently there would be one nestling and one egg. Sometimes this egg was spoiled, 

 sometimes contained an embryo. In one case I found two newly hatched young, 

 one of which had aU-eady been trampled to death. Professor Nutting saw one 

 large nestling and one small, still alive, but I doubt if it lived long. The presence 

 of only one young bird has been noted in the eastern Pacific at Clipperton Island 

 by R. H. Beck, and Rothschild mentions the same fact for Laysan. The voracity 

 of the bird first hatched is probably responsible for the death of the second. 



The young bird nearly always keeps its head under the parent, although the 

 greater part of its body may be exposed to the sun. Both old birds take turns in 

 sitting on the eggs or watching the nestling. Occasionally both will be seen 

 standing guard together in an absurd statuesque pose, or gazing seaward or at 

 the sky on the lookout for winged marauders. From time to time they utter 

 a very hoarse strident cry. 



The young are fed on semidigested food ; the process is described 

 by Doctor Fisher (1906) as follows: 



The young one inserts its head fairly into the throat of the parent, in a de- 

 cidedly gruesome manner, and catches the disgorged food. In fact, the young 

 one's head went so far into the parent's throat that I became solicitous for its 

 safety. Flying fish, swallowed whole, seem to be their favorite food, judging by 

 remains scattered about nests and a stomach examined. 



When the old birds exchange places, one slips off the nestling and the other 

 immediately takes its place, as if fearing an attack from a frigate bird. The 

 boobies appear to exhibit affection for their young. I have seen them gazing 

 at the fuzzy-white ball with evident pride in their otherwise stolid countenances, 

 and on one occasion saw an old bird carefully lay dry sedge over the exposed 

 and not too heavily feathered hind parts of the young. 



Plumages. — The young is covered with soft, thick, yellowish-white 

 down. The immature, or first year, plumage is described by Dr. 

 Thomas H. Streets (1877) as follows: "The brown color of the back 

 and upper surface of the wings has a grayish tinge; the head and 

 neck all around dark brown, as in /S. leucogastra, except that the dark 

 color does not extend as far down, in the breast as in the latter." 

 There is not sufficient material available to show the subsequent se- 



