BIEDS OF PENNSYLVANIA. 



183 



tumn they collect in large flocks before retiring- to their winter resorts. 

 I have observed birds of this species in Chester county (Pa.), as late as 

 the 20th of October. In this locality the nest of the Chimney Swift, or 

 Swallow, as it is mostly called, is composed of small twigs, which are 

 glued together and to the sooty walls of disused chimneys with the bird's 

 saliva.* The twigs used in constructing nests are broken off of trees by 

 these birds when on the wing. The eggs, four or six in number, are 

 white and unspotted. They measure about three fourths of an inch in 

 length and about half an inch in width. 



These birds subsist entirely on various kinds of insects which they 

 collect during the night as well as in daylight. 



The food materials of twelve birds which I have examined are men- 

 tioned below : 



SUBORDER TEOCHILI. HUMMINGBIRDS. 

 FAMILY TROCHILID-ffi. HUMMINGBIRDS. 



GENUS TROCHILUS LINNAEUS. 

 Trochilus colubris LINN. 



Ruby-throated Hummingbird. 



DESCRIPTION (Plate 56). 



Male. Tail deeply forked, the feathers all narrow and pointed ; uniform metallic- 

 green above ; sides of body greenish ; below white ; ruby-red gorget ; wings and tail 

 purplish-black. 



Female. Metallic green of upper parts duller than in male ; tail double rounded ; 

 its feathers pointed but broader than in male; no red on throat ; the tail feathers 

 banded with black ; the lateral ones broadly tipped with white. 



Young Male. Very similar to adult female, but throat more or loss streaked with 

 dark ; tail also more forked than in female. Nearly all specimens show a trace of 

 metallic red on throat. 



Young Female. Throat white, without streaks or specks ; tail less forked, other- 

 wise similar to young male. Irides in old and young brown. Length about 3.25 

 inches ; extent of wings about 5 inches. 



* A. writer in a recent scientific journal, which 1 have mislaid, says : " In the case of our own Chimney 

 Swifts it has lately been shown that the gelatinous matter with which the twigs are fastened together is 

 of a vegetable and not an animal character, and in a particular case recently investigated by a scientist, 

 the Kinn was found t<> have come from a cherry tree. " 



