PHILADELPHIA VIREO 353 



other birch in the vicinity. When lie found the birds biiikling, on 

 July 7, they had woven only a few strands close up in the crotch of 

 the twig; two days later it was nearly finished, and on the 10th it 

 was all done. On July 15, he wrote in his notes : "The first egg must 

 have been deposited on the 12th, for I climbed to the nest for the 

 first time on the 13th, when it contained two eggs and the bird was 

 on the nest ; today, when I climbed to it, she sat very close and allowed 

 me to part the leaves that partly hid the nest; I watched her fully 

 five minutes and then she flew only when I put my hand within six 

 inches of her. Up to then, she had simply raised her head and 

 watched me closely ; and how pretty she was with her yellowish white 

 throat ! When she flew, she kept out of sight for about ten minutes, 

 and then returned and moved about in a nearby tree, but did not 

 scold as vireos do." 



He found another nest in the same locality on June 29, 1909. This 

 was 40 feet from the ground in a thick maple, a lone tree among 

 spruces, on the edge of heavy spruce timber at the top of a ravine. 

 Both nests contained full sets of four eggs each. 



Mr. Terrill has sent me a photograph (pi. 45) of a nest that he 

 found 8 feet from the ground in an alder along a small stream ; this 

 nest had some birch bark in its composition, as well as a quantity of 

 usnea, which can be seen hanging below the nest; he says that the 

 use of usnea in the nest is diagnostic. 



Eggfi. — From three to five eggs may constitute a full set for the 

 Philadelphia vireo, four being the commonest nmnber and five very 

 rare. These are very much like the eggs of the red-eyed vireo, 

 though slightly smaller. Mr. Brewster (1903) describes his eggs as 

 "elongate ovate in shape and pure white, sparsely spotted with burnt 

 umber, chocolate and dull black." Philipp and Bowdish (1917) say 

 that their eggs "were white with dark brown spots and specks, the 

 larger spots tending to have a rusty border". Mr. Doe's eggs are 

 marked on the large end with dark reddish brown. The scanty mark- 

 ings are sometimes scattered over the whole surface, but more often 

 nearer the larger end of the egg. The measurements of 50 eggs average 

 19.2 by 14.0 millimeters ; the eggs showing the four extremes measure 

 21.7 by 14.9, 21.6 by 15.3, 17.8 by 14.0, and 18.5 by 13.0 millimeters. 



Young.— Qv. Lewis (1921) found the incubation period for the 

 Philadelphia vireo to be about 14 days. He saw the male relieve the 

 female and sing while incubating on the nest. Mr. Brewster (1903) 

 also saw the male singing on the nest. In the nest that Dr. Lewis 

 studied the first ^^g hatched on June 29; during that afternoon the 

 pair changed places on the nest at very frequent intervals. "During 

 the hour and twenty-five minutes between 12.40 p. m. and 2.05 p. m. 

 the pair had exchanged places on the nest eight times, the intervals 

 between reliefs being sometimes as short as three, four, or six minutes." 



