158 BULLETIN 17 0, UNITED STATES NATIONAL MUSEUM 



white and oval ; the shell is smooth and rather glossy. The measure- 

 ments of 103 eggs, in the United States National Museum, average 

 40 by 32.5 millimeters; the eggs showing the four extremes measure 

 43.5 by 33.5, 43 by 35, 37.5 by 31, and 38.5 by 30 millimeters. 



Young. — The incubation period is generally considered to be about 

 21 days. An egg is laid about every other day, and since incubation 

 begins when the first egg is laid the young hatch at similar intervals 

 and show considerable variation in size. It does not seem to be known 

 whether the male assists in incubation, but he is always close at hand, 

 while the female is incubating, during the day at least, and responds 

 quickly to her cries of distress. Probably he hunts for food at dusk 

 and during the night and may feed his mate on the nest or relieve her 

 to hunt for herself. 



When between four and five weeks old the largest young birds begin 

 to leave the nest, crawling out onto the surrounding branches. All 

 leave the nest long before they can fly, climbing about or fluttering 

 down to perch on any low branch or fallen tree. They are carefully 

 guarded by both parents during this period, who rush to their defense 

 and attempt to lure an intruder away by spectacular demonstrations. 

 They are fed by their parents until they are at least eight or nine 

 weeks old, have gained the full power of flight, and have learned to 

 hunt for themselves. The family group keeps more or less together 

 during summer and fall and perhaps during winter. 



The calls of the young, described below by William Brewster 

 (1925), are evidently their cries of distress that call their parents to 

 their defense; at least they produced that result each time that he 

 heard them. He writes: 



They were perched together on a fallen branch about five feet above the 

 ground, to which they must have fallen or fluttered down not long before, from 

 a nest that could be seen high in a pine directly overhead, for having wing- 

 quills scarce more than one half grown they were incapable of level flight. When 

 closely approached they behaved precisely like the young found in 1874 [crouch- 

 ing in a nest, see below under "Behavior"], and made essentially the same sounds 

 although the blowing ones heard to-day were less suggestive of "snoring" than of 

 the hissing or "spitting" of an angry house-cat, and the crick-a-crick calls seemed 

 more like the chirping of a field-cricket than the squeaking of a wheelbarrow. 



E. L. Sumner, Jr. (1929), in his studies of a brood of young long- 

 eared owls, found that the egg tooth disappeared during the first 

 week, but the young were very sluggish and inactive; even the oldest 

 made no protest other than a feeble hiss, and all the rest were silent. 

 Eleven days later, he says: "The largest three youngsters are quite 

 aggressive, standing up with outspread wings inverted and every 

 feather erect, winch gives them a deceptively bulky appearance. 

 They snap viciously at my outstretched finger, and sway from side 

 to side — a trait not exhibited by any of the hawks — but are as yet 

 perfectly harmless. With the exception of the oldest, they make no 



