340 BULLETIN 16 7, UNITED STATES NATIONAL MUSEUM 



great birds. Mucli of what follows has been taken from his published 

 papers (1924a, b, c, and d, 1929, 1932, and 1933). He gives the period 

 of incubation as 31 to 35 days under normal conditions, though in- 

 terrupted incubation may require a somewhat longer time. Both 

 sexes share in the duties of incubation and care of the young; of 

 which he (1929) writes: 



In conducting the shifts a rather definite formula was observed. The sitting 

 bird would give a sharp chitter when wishing to be relieved ; the mate, if within 

 hearing, came to the eyrie, moved up close, and the exchange was quickly 

 made. If the eggs were left for only the shortest time, they were carefully 

 covered with a great quantity of grass, stubble, and other convenient nest 

 material, and the scrupulous covering and uncovering process would sometimes 

 last from five to ten minutes. * * * 



The eagle is the greatest home-keeper of his class. His eyrie is his castle, 

 which, as we have seen, he will at times defend against all comers. In it his 

 eaglets spend the first ten weeks of their life — from mid- April until early July, 

 upon the southern shore of Lake Erie — and it is the occasional rendezvous, 

 lookout point, and dining table for the elder pair for the remainder of the year. 



In his final paper (1933) he writes: 



Many times I have been impressed by the behavior of the mother eagle 

 when rain or hail descended upon her down-clad young. As I approached 

 the woods one mid-May morning the female eagle was on the nest, and 

 whether because of seeing me or not, she presently withdrew to a tree-perch. 

 Then, just as I entered the grove a brisk shower started, and the eagle at 

 once returned to her young ones. Frightened at my ascent of the tower, she 

 was off again, but, as the shower continued, returned in a few moments after 

 I had entered the tent. She stood facing the wind and rain, with half-open 

 wings, and afforded good shelter for the month-old eaglets huddled beneath 

 her. In a few minutes this shower passed, and as the sun broke out she 

 went back to her perching tree and spread her drooping wings to dry, in 

 precisely that attitude assumed in times of great heat and humidity. Now, 

 a quarter of an hour had hardly passed before the clouds again closed in and 

 darkened above us; another downpour was under way, and the faithful mother 

 sped back to her charges, and there she remained fending them with her stal- 

 wart body until this final shower was over. * * * Branches of pine and 

 other green vegetation were always brought to the Vermilion nests both 

 early and late in the season, and leaves were occasionally eaten by both adult 

 and young eagles, as proved by their castings, but what significance this may 

 have, if any, has not been ascertained. 



He says elsewhere (1924c) : "In 1923, if our estimate of the incu- 

 bation period is correct, Eaglet No. 1 spent seventy-two and Eaglet: 

 No. 2 seventy-four days, in this case continuously, in the eyrie. 

 Allowing then from 10 to 11 weeks for the life of the young Eagles 

 in the nest, about one-half of this period, or five weeks, is passed 

 in the white and gray down stages and the other half in the juvenal 

 dress." 



Although often two, and sometimes three, eaglets are hatched, the 

 larger number is seldom raised to maturity, and often only one 



