168 BULLETIN 2 03, UNITED STATES NATIONAL MUSEUM 



with blotches a quarter of an inch in diameter, often they are only 

 finely speckled with the gray undertones. The measurements of 50 

 eggs average 16.6 by 12.6 millimeters; the eggs showing the four 

 extremes measure 17.8 by 13.2, 17.8 by 13.7, 15.2 by 12.7, and 15.8 by 

 11.7 millimeters (Harris). 



Young. — The incubation period for the eastern yellow warbler has 

 been recorded as from 8 to 11 days (most observers place it as about 

 11 days for each individual ^gg) ; often, but not always, it begins 

 before the set is complete, making the period appear shorter for the 

 first ^gg laid. Eggs are generally, though not always, laid on suc- 

 cessive days, but at times 1 or 2 days intervene between layings. In- 

 cubation is performed wholly by the female. The male stands guard 

 near the nest and feeds the female while she is sitting, but she also 

 leaves occasionally to feed herself. The young remain in the nest 

 from 8 to 15 days, according to several observers, but here again the 

 normal time is probably between 9 and 12 days, if they are undisturbed. . 



Harry C. Bigglestone (1913) describes the hatching process as 

 follows : 



At about 5 :30 a. m. on July 3 tlie writer was attracted by a peculiar rolling 

 motion of the egg in the nest, and noticed upon closer observation, that the 

 shell bulged out in a ring around the middle or a little nearer the smaller end ; 

 and soon it began to crack at this place. The egg raised on the small end, lean- 

 ing against the side of the nest, and the young bird freed himself from the shell 

 by a series of pushes and kicks by the head and feet, respectively. The head 

 escaped from the larger part of the shell and the lower part of the body from 

 the smaller end. The crown of the head and the median line of the back of the 

 nestling were downy. This entire process covered a period of less than four 

 minutes. 



The empty shells were broken up and eaten by the parents. He says 

 that brooding was carried on entirely by the female, except that he 

 once saw the male brooding for 7 minutes, and adds : 



The female was more careful in brooding the young during the first few days. 

 She would stop for intervals throughout the day, while feeding, and brood the 

 young. Her way of completely covering the brood was to fluff out the under 

 coverts against the rim of the nest and bring the wings down, just inside, so 

 as to effectually close the nest. 



* * * The female had different brooding attitudes for the varying circum- 

 stances. For protection against the cold of early morning she brooded in the 

 manner described above, completely covering the young. Through the rains she 

 brooded in much the same way as for cold, sheltering the young, so that after 

 an unusually heavy downpour, the nest remained perfectly dry inside. During 

 the heat of midday she usually stood in the nest with wings spread, shielding 

 the young, but without shutting off the circulation of the air. On the contrary, 

 at times she gently flapped her wings, as if fanning the young. During the 

 strong winds she stood in the nest with wings outstretched, and leaned in the 

 direction of the wind, so as to secure a delicate balance and at the same time 

 keep tJie young in the nest. 



