The nest is almost invariably placed upon the ground, in a thick bed of dry leaves, in a clump of grass, at the roots of low bushes, or under the shelter of a pile of brush, sometimes being covered by surrounding leaves, and quite as often exposed from above. When built directly upon the ground, it occupies a depression thereof; but when built in a tussock, this precaution is not taken, as the necessary security is afforded by the enveloping grasses or sedges. According to Dr. Brewer, nests are occasionally found four or five feet from the ground, among the matted branches of high weeds. A typical nest consists of loose leaves on the outside, which are held in position by the walls of the cavity in which they are placed, or by surrounding grasses. Within is placed a superstructure of dry grasses, twigs, strips of dry bark, and leaves of sedges. The lining consists of fine strips of the bark of the chestnut and wild grape vine, which are arranged with great care and compactness. In depth these structures vary from five to six inches, and have an external diameter of two and a half inches at the base, and three at the mouth. The cavity is usually three inches deep, and about two and a quarter wide. When we come to compare the entire fabric with the size of the builder, we are at a loss to account for the disproportion.
The work of building such a bulky domicile does not fall to the lot of the female solely, but is the result of the combined labor of both birds, who prosecute their task with commendable diligence and patience for a period of five days, when they are rewarded with the sight of a finished home. Nothing now remains to be done but to furnish the capacious apartment with its wee, spotted treasures. This cannot be commenced immediately, as sufficient time must be allowed for the walls to become properly seasoned. Two or three days at the utmost are all that are necessary. On the fourth day the female deposits her first jewel, and, where not interrupted, renews the same duty day by day, until she has furnished her allotted quota. She immediately commences the incubating process, occasionally not before the succeeding day, and for ten long days is thus engaged, when the appearance of the young reminds her that the labor is ended. While thus employed the male, actuated by the purest affection, administers to her necessities with commendable alacrity. He only forsakes her for food. When the nest is assailed, by the most pitiful cries and the practise of various ruses, he endeavors to lead his enemies away from it. His stratagems often succeed with the unsophisticated, but with the professional collector they are of little avail.
The young are carefully nurtured. Their food consists of the larvæ of small beetles, caterpillars of various kinds, and diptera. At the age of twelve days they are able to leave the nest, but remain under parental surveillance for a week longer, when they are obliged to shift for themselves, being permitted, however, to enjoy the society of their parents. Early in September, both young and old take their departure, the greater portion retiring to Mexico, Guatemala and the West Indies, while a few remain along our southern borders.
The plumage of the young bird is brownish-olive above, with a tendency to stronger virescence on the rump and tail. The eyelids and entire lower parts are a light buff, which is relieved by a tinge of yellow on breast and lower tail-coverts. The male in the spring is olive-green, somewhat grayer anteriorly, and has the forehead and a broad band through the eye to the neck a pure black, margined superiorly with grayish-ash. The chin, throat, breast, under tail-coverts and edge of wing bright yellow, passing into whitish in the abdominal region. The wings and tail are slightly olive, and devoid of marks. The bill is black, and the feet flesh-colored. In the female, during the same season, the crown is generally brownish, the black and ash on the head wanting, and the yellow of the under parts pale and restricted. From its congeneric brethren this species differs in the absence of a clear ash upon the throat. Its length is about four and three-fourths inches, wing two and one-fifth, and tail two and three-tenths.
The eggs of the Yellow-Throat range from four to six in number, the complement doubtless depending upon locality, and the peculiarity of the female. In Eastern Pennsylvania, Southern New Jersey and Delaware never more than four have been found in a nest, and this has been the experience of others from even the most widely separated localities. In color the eggs are a beautiful crystalline-white, and are dotted and blotched around the larger extremity with reddish-brown and dark umber. Specimens are often found with curiously-shaped lines and dashes of remarkable fineness. Their size varies with latitude, the largest coming from Kansas, and the smallest from Georgia. The average measurement of several sets from four different localities is .04 by .53 inches. We incline to the opinion that but a single brood is annually raised, although there may be instances where more than one has been observed. In most cases, where the birds have been late in rearing their young, the hasty collector, and even recorder of facts, may conclude that he has a sure proof of his position. Careful watching, carried through a decade, has convinced us that in Philadelphia the species is single-brooded. Like most of our smaller birds, the nest of this species does not escape the visits of the Cowbird, who, taking advantage of the absence of its owners, embraces the opportunity of depositing two of her own eggs, which she trusts the female Yellow-Throat will adopt and rear as her own.
