Some of the foster parents abandon their nests, or build a second nest over the eggs, but usually the little bird works faithfully to bring up the foundling. Sometimes the egg is recognized by the mother and quickly thrown out. Frequently, also, the cowbird will eject one or more eggs of the owner to make room for her egg, or to deceive the owner and leave the same number of eggs as were in the nest before her visit. Sometimes an egg of the owner is found on the ground near a nest containing an egg of the cowbird, and it is no unusual occurrence to find an egg of the cowbird lying near a nest of a species regularly imposed upon by the parasite. Silloway says that the wood thrush, towhee, field and chipping sparrows, yellow-breasted chat, and the Maryland yellow-throat are oftenest selected to bear the burden of rearing the young of the cowbird. In their courtship the males are very gallant. They arrive from the south several days in advance of the females. At this season--about the middle of March--they generally associate in groups of six or eight, and the males are easily distinguished by the gloss of their black plumage in contrast to the dull brown of the female. They do not pair, the females meeting the advances of the males indiscriminately. Dr. Gibbs, however, thinks that the birds may pair frequently for the summer, and suggests this as reasonable, referring to an incident coming under his notice when he saw a blue jay, on the point of despoiling the nest of a vireo, driven away by a pair of cowbirds in a most valiant manner. In going to the nest he found a large over-grown cowbird occupying the largest share of the structure, "while a poor little red-eyed vireo occupied a small space at the bottom, and beneath his big foster brother." The eggs of the cowbird hatch in eleven or twelve days. They average .88 by .65 of an inch, the length varying from .95 to .67 of an inch, and the width varying from .72 to .58 of an inch. The ground is a dingy white or gray, and the markings vary through all the shades of brown, sometimes evenly distributed over the surface, and at other times predominating around the larger end. There is so much diversity in the appearance of different specimens, that frequently the investigator is puzzled in distinguishing the true eggs of the towhee, cardinal, and other species from those of the cowbird. In the breeding season the male grackles, red-winged blackbirds, and the cowbirds of both sexes, nightly congregate to roost together. Early after the breeding season they form into flocks of from fifty to sixty. The birds have then finished moulting, and the glossy black of the males has been changed into the duller colors of the females and the young. They assemble with the blackbirds of various species where food is most abundant and easy to be procured.