Any attempt at disturbance or pillage is resented with spirit and courage, especially when the nest contains young birds.
The home of this Vireo is often chosen by the Cowbird as a place of deposit for her eggs. So singularly devoted to their alien guests do these foster-parents become, that they nurture them very tenderly, even to the neglect of their own offspring. A case is mentioned where three of these parasitic eggs had been deposited in the nest of the Vireo before any of her own. Without laying any, the female Vireo proceeded to set upon and hatch the intruders. Another case is cited where two Cowbird's eggs were laid alongside of two of the Vireo's. The latter immediately stopped laying and proceeded to incubate. In each of these cases it is evident that the female Vireo forewent her own maternal instincts, and at once conformed to the new situation.
The young are objects of special parental interest. From the time they are hatched, until the period of their leaving the nest to earn a livelihood, they are watched over, and fed with the daintiest fare which Nature affords. Caterpillars, diptera, plant-lice, small spiders and berries, constitute their earliest diet; but as they increase in size and strength, other articles of a coarser nature are added. At the age of twelve days they vacate the nest, but continue under the watchful eyes of their parents a week longer, when they are able to forage for themselves.
The anxieties of brood-raising being over, both young and old, the former in imitation of their parents, seek the tall tree-tops and glean in company. Later, they come down from these lofty retreats to delve among the grasses. Finally, as if disdaining too near an approach to earth, they quickly forsake such groveling pursuits, and seek the viburnum and dogwood bushes, where they find many a rich repast. Here they remain until the last of September, or the beginning of October, when cold weather and scarcity of food compel them to hunt warmer climes.
The eggs of this Vireo vary considerably in size, according to locality; the further south the smaller they are found. Specimens from Northern Alabama have an average measurement of .77 of an inch by .52; from Nova Scotia, .94 by .65; from Pennsylvania and Massachusetts, intermediate localities, .82 by .56, and .83 by 62. The ground-color of all is a clear crystal-white, and they are marked with spots and fine dots of red-brown, which are chiefly found at the larger extremity. But a single brood is raised, although nests with eggs have been taken early in July, which must be attributed to birds whom accident or design had prevented from obeying their natural instincts earlier.
