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. The song of the Summer Yellow-Bird is simple but pleasing, and is easily recognized when once known, though liable to be confounded with that of the Maryland Yellow-Throat, and also said to resemble the song of several other Warblers. In confinement they usually become very tame, confiding, and reconciled to their imprisonment, and have been known to perch on an outstretched finger, and to catch flies in a room.