390 BULLETIN 17 9, UNITED STATES NATIONAL MUSEUM 



Young. — Austin and Low (1932) from a study of a large number 

 of nests "found the length of the [incubation] period, estimated from 

 the day the last ^^% was laid to the day the first one hatched, to vary 

 from a minimum of 13 days to a maximmn of 16." According to their 

 records the young birds remained in the nest 16 to 24 days, and to ac- 

 count for this variation they point out "that the most food per young 

 will be delivered in those nests containing the fewest nestlings, and 

 hence the rate of growth will be slowest where the broods are largest." 

 They state that "at no time were the young birds observed to return 

 to the boxes once they had flown." Winton Weydemeyer (1934b), 

 however, says: "For a few days after taking to the air, the young 

 birds enter and leave the houses frequently, and remain in them all 

 night." 



The nestling tree swallow is an attractive little bird when, well 

 grown, it comes to the doorway and peers about, watching for its par- 

 ents to come through the air with food. As it waits at the entrance 

 its low forehead and immaculate throat call to mind a little frog sit- 

 ting there in the box. Its eyes shine eagerly, and when the parents 

 come near it stretches out toward them, its throat gleaming white 

 against the dark interior. 



A, Dawes DuBois (MS.) says : "The young are strong of wing when 

 they leave the nest." He speaks of one young bird which "took to the 

 air like a veteran, both parents accompanying it." Austin and Low 

 (1932) state that "usually they showed remarkable ability on their 

 first flight, often remaining in the air well over a minute, and flying 

 a quarter of a mile." George Nelson tells me that he has often watched 

 the young birds leave the boxes in his garden. They launch out, then 

 fall, fluttering, nearly to the ground sometimes, when, of a sudden, 

 the power of flight comes to them, and they rise into the air and fly 

 off, seemingly as ably as their parents. 



Plumages. — [Author's note : The juvenal plumage of the tree swal- 

 low is quite unlike the plumage of either adult. The upper parts, 

 including the sides of the head and neck, are dark sooty brown or 

 very dark brownish gray, "dark mouse gray", without any trace of 

 the iridescent bluish green of the adult plumage but with a fine silky 

 gloss. The feathers of the interscapular region are at first faintly 

 edged with pale fawn color, but these edgings soon wear away. The 

 wings and tail are slaty brown, with slight greenish reflections, the 

 secondaries and tertials with faint grayish edges and tips. The under 

 parts are duller white, less silky, than in the adult ; and there is a very 

 faint and incomplete pectoral band of ashy brown. 



A complete post juvenal molt takes place, beginning late in August 

 and continuing into October. This produces a first winter plumage, 

 which is practically indistinguishable from the winter plumage of 

 the adult. Dr. Dwight (1900) says of this plumage: "Above irides- 



