188 BULLETIN 16 7, UNITED STATES NATIONAL MUSEUM 



average 54.7 by 43.9 millimeters ; the eggs showing the four extremes 

 measure 59 by 47, 51 by 41, and 53 by 40 millimeters. 



Young. — The period of incubation is about 28 days, and it is shared 

 by both sexes. I have seen the pair change places on the nest; the 

 male comes flying low through the woods, screaming, and alights on 

 the edge of the nest with an upward glide ; the female rises up in the 

 nest (sexes assumed) and flies away, and the male settles on the eggs 

 ao once. The male also feeds the female while she is incubating. 

 Once, after I had been watching a bird on a nest for over an hour, 

 her mate flew up, bringing a mouse in his bill; he stood beside her 

 on the nest, gave her the mouse, and then quickly flew away ; she rose 

 up off the eggs, stood on the side of the nest, and ate the mouse, pull- 

 ing it to pieces and swallowing it in small bits; this took about five 

 minutes, after which she settled down on the eggs as before. I have 

 also seen a hawk come to a nest, where his mate was incubating, leave 

 food on the nest, and fly away, after which she stood up and ate the 

 food. I have spent many liours in a blind watching hawks at their 

 nests. The blind must be well hidden and offer perfect concealment ; 

 a brush blind is useless, as their eyesight is very keen; they will 

 detect the slightest movement, leave the nest at once, and will not 

 return to it if they know that they are watched. Much of the time 

 while incubating the hawk is alert, with head raised and constantly 

 looking about; at such times she will fly if anyone approaches the 

 tree; at other times I have seen the same bird apparently asleep on 

 tiie nest, with her head invisible, when I could walk up and pound 

 the tree before she would leave. Once a hawk that I had been watch- 

 ing for some time rose up and stood on the edge of the nest for 10 

 minutes, looking around, then settled down on the eggs and went to 

 sleep ; I had to pound the tree to make her fly. 



On May 20, 1932, I saw the whole process of feeding a brood of 

 three young; they were about one-third grown but still all downy; 

 they were very lively, constantly moving about, voiding their excre- 

 ment over the edge of the nest, and looking up into the sky, appar- 

 ently hungry. At 9.55 a. m, a hawk flew over screaming but did not 

 come to the nest, and at 10.15 the same thing happened again, the 

 young watching eagerly. At 10.30 a hawk came to the nest, appar- 

 ently left some food and flew right away ; about 10 minutes later this 

 happened again. The young made no attempt to eat the food. At 

 11 a, m. the female, presumably, alighted on the edge of the nest and 

 proceeded to feed the young; she tore the food (I could not see what 

 it was) into small bits and fed the three young as nearly in succession 

 as she could ; they took the pieces from her bill, and she swallowed a 

 piece occasionally herself. Competition was keen, and in the struggle 

 the largest one got more than its share, taking several pieces in suc- 

 cession; when it had enough it turned its back on its mother and 



