378 BULLETIN 17 0, UNITED STATES NATIONAL MUSEUM 



in the top of a dead tree 15 feet from the ground." Both sets of eggs 

 were fresh. 



Eggs. — The American hawk owl lays three to seven eggs, the latter 

 number quite frequently, and rarely as many as nine. The eggs vary 

 in shape from oval to elongate-oval, the color is pure white, and the 

 shell is smooth and slightly glossy. They closely resemble the eggs 

 of the short-eared owl. The measurements of 51 eggs average 40.1 

 by 31.9 millimeters; the eggs showing the four extremes measure 

 43.3 by 31.2, 40 by 34, and 36.5 by 30 millimeters. 



Young. — The period of incubation does not seem to have been 

 definitely determined; this would be a difficult matter, as the eggs 

 are laid at some intervals, and incubation begins as soon as the first 

 egg is laid. The nest that Dr. Grinnell (1900) found — 



contained three newly-hatched young and six eggs in various advanced stages of 

 incubation. The downy young, although their eyes were still tightly closed and 

 they were very feeble, uttered a continuous wheedling cr} r , especially if the tree 

 were tapped or they were in any way jarred This could be heard 20 feet away 

 from the base of the tree. The nest cavity was evidently an enlarged woodpecker's 

 hole. The wood was very much decayed and soft, so that it has been an easy 

 matter to enlarge the entrance. The entrance was 14 feet above the snow, and 

 the nest proper was about three inches below that. The cavity was lined with a 

 mixture of feathers and bits of the rotten wood. The feathers were all apparently 

 from the breast of the female parent. The female bird (the male not at all, 

 although he was sitting on the nest when it was found) had the whole breast and 

 abdomen, from the upper end of the breast-bone to the vent, entirely bare of 

 feathers; also on the sides up to the lateral feather tracts, and through these for 

 about one inch on both sides under the wings; also down the inside of the thighs 

 to the knees. This was the most extensive feather divestment I ever saw in any 

 species. The skin of this area was very thick and glandular, emitting a watery 

 fluid on the inside when squeezed, and filled with distended blood vessels and 

 Borne fat. This is obviously a warmth-producing organ. The feathers removed 

 from it were evidently mostly used in the nest lining. 



Although both sexes share the duties of incubation, it is evident 

 from the above that the female does most of it. While one parent is 

 incubating, the other remains on guard in the vicinity to guard the 

 nest most aggressively. And Dr. A. K. Fisher (1893b) says that 

 "after the young leave the nest the family generally remain together 

 until the following spring." 



L. L. Snyder (1928) writes: "The notes of the young birds are 

 decidedly like those of the broad-winged hawk, except thitt the high- 

 pitched, hissing sound ascends slightly towards the end. An adult 

 was observed hunting mice for its flying young along a creek bed at 

 Camp 33. The hissing calls of its four or five young could be heard 

 from as many directions, unquestionable reminders to the parent that 

 they were there, and hungry. The parent, leaving its perch in the 

 open, gently settled for an instant in the grassy edge of the creek and 

 rose with a meadow mouse in its feet. One of the young was quieted, 



