Its extreme southern limit is not so distinctly traced, but is at least as far as the northern portions of South America, inclusive of Cayenne and Ecuador. In all of the West Indies except Trinidad it is replaced by several closely allied species or local races. In Trinidad, Mr. E. C. Taylor states that he found this species common, and could perceive no difference from North American specimens. In Guatemala it is abundant in the winter.
Dr. Coues found this Warbler abundant in Arizona, where it is a summer resident, from April 25 to the middle of September. There, as elsewhere, its preference for watercourses was noticed. Wherever found, it is always most abundant in alluvial meadows, and more rare in other localities.
Dr. Samuel Cabot found this Warbler common in Central America, and Dr. Cragin, of Surinam, sent the Boston Society several specimens from Guiana. Dr. Woodhouse found it abundant in Texas and New Mexico, as did Drs. Suckley and Cooper in Washington Territory and California. It breeds over the whole area of North America, from Georgia on the southeast and from Mexico, northward. Dr. Sumichrast found it, only as a migratory bird, abundant on the plains of Mexico.
The notes of Mr. Kennicott and the memoranda of Messrs. McFarlane, Ross, and Lockhart attest the extreme abundance of this species in the farthest Arctic regions. In nearly every instance the nests were placed in willows from two to five feet from the ground, and near water. In one instance Mr. Ross found the eggs of this species in the nest of Turdus swainsoni, which had either been deserted or the parent killed, as the eggs were in it, and would probably have been hatched by the Warbler with her own.
Dr. Cooper found this Warbler very abundant in Washington Territory, and noticed their arrival in large numbers at the Straits of Fuca as early as April 8.
The Summer Yellow-Bird arrives in New England with great uniformity from the first to the middle of May. Its coming is usually the harbinger of the opening summer and expanding leaves. Unlike most of its family, it is confiding and familiar, easily encouraged, by attention to its wants, to cultivate the society of man. It confidingly builds its nest in gardens, often in close vicinity to dwellings, and in the midst of large villages and cities, among the shrubbery of frequented parks. This Warbler, soon after its arrival, begins the construction of its nest. It is usually placed in low bushes, three or four feet from the ground. Occasionally very different positions are chosen. Hedges of buckthorn and hawthorn, barberry-bushes, and other low shrubs, are their favorite places of resort. On one occasion the nest was placed some forty feet from the ground, in the top of a horse-chestnut tree overhanging the main street of a village. Such high positions are, however, not very common.
The nest is invariably fastened to several twigs with great firmness, and with a remarkable neatness and skill. A great variety of materials is employed in the construction of their nests, though not often in the same nest, which is usually quite homogeneous. The more common materials are the hempen fibres of plants, fibrous strips of bark, slender stems of plants and leaves, and down of asclepias. Interwoven with these, forming the inner materials, are the down from willow catkins, the woolly furze from fern-stalks and the Eriophorum virginicum, and similar substances. These are lined with soft, fine grasses, hair, feathers, and other warm materials. Cotton, where procurable, is a favorite material; as also is wool, where abundant. I have known instances where nests were built almost exclusively of one or the other material. A pair of these birds, in 1836, built their nest under a parlor window in Roxbury, where all their operations could be closely watched. When discovered, only the framework, the fastening to the supporting twigs, had been erected. The work of completion was simple and rapid. The female was the chief builder, taking her position in the centre of the nest and arranging the materials in their places as her mate brought them to her. Occasionally, with outstretched wings and expanded tail, she would whirl herself round, giving to the soft and yielding materials their hemispherical form. At intervals she arrested her revolutions to stop and regulate with her bill some unyielding portion. When her mate was dilatory, she made brief excursions and collected material for herself, and when the materials brought her were deemed unsuitable, they were rejected in a most summary and amusing manner. The important part of the tail-feathers in shaping the nest and placing the materials in position was a striking feature in this interesting performance. The greater portion of the nest was thus constructed in a single day.
The wonderful sagacity displayed by this Warbler in avoiding the disagreeable alternative of either having to abandon its own nest or of rearing the young of the intrusive Cow Blackbird, when one of these eggs is dropped in her nest, was first noticed by Mr. Nuttall. The egg of the parasite, being too large for ejectment, is ingeniously incarcerated in the bottom of the nest, and a new lining built over it. Occasionally, either by accident or design, the intrusive egg has been fractured. Mr. Nuttall states that where the parasitic egg is laid after her own, the Summer Yellow-Bird acts faithfully the part of a foster-parent. This, however, is not according to my observations. In several instances I have known the Summer Yellow-Bird utterly refuse to act the part of a foster-parent, and, rather than do so, sacrifice her own eggs. So far as I know, this Warbler will never sit upon or hatch out the egg of the Cowbird, under any circumstances. Some powerful instinct, bordering closely upon reason, seems to teach these intelligent Warblers the character of the intruder, and they sacrifice their own eggs rather than rear the parasite. In this dilemma they will always, so far as I know, incarcerate their own eggs with the Cowbird’s and reconstruct the nest above them. In one instance the same pair of Yellow-Birds twice, in the same nest, covered up alien eggs in this manner, building, in fact, three nests one above the other, between the walls of which had been successively included two eggs of the Cowbird. This three-storied nest measured seven inches in length, and was built almost exclusively of raw cotton. The covering of the imprisoned eggs was about two thirds of an inch thick. In both instances the Cowbird’s eggs had been broken, apparently by design.
So far as I am aware this Warbler raises but one brood in Massachusetts in a season. In Pennsylvania it is said to raise two, and even three. The eggs are usually five and occasionally six in number.
This Warbler is conspicuous in its devotion to its young, evincing a strong attachment and an anxiety in regard even to an unoccupied nest, and betraying the site by this solicitude. They will also resort to various expedients to draw one away from their nest, by feigned lameness and other stratagems and manœuvres.