This species is at all times gregarious and polygamous, never mating, and never exhibiting any signs of either conjugal or parental affections. Like the Cuckoos of Europe, our Cow Blackbird never constructs a nest of her own, and never hatches out or attempts to rear her own offspring, but imposes her eggs upon other birds; and most of these, either unconscious of the imposition or unable to rid themselves of the alien, sit upon and hatch the stranger, and in so doing virtually destroy their own offspring,—for the eggs of the Cowbird are the first hatched, usually two days before the others. The nursling is much larger in size, filling up a large portion of the nest, and is insatiable in its appetite, always clamoring to be fed, and receiving by far the larger share of the food brought to the nest; its foster-companions, either starved or stifled, soon die, and their dead bodies are removed, it is supposed, by their parents. They are never found near the nest, as they would be if the young Cow Blackbird expelled them as does the Cuckoo; indeed, Mr. Nuttall has seen parent birds removing the dead young to a distance from the nest, and there dropping them. For the most part the Cowbird deposits her egg in the nest of a bird much smaller than herself, but this is not always the case. I have known of their eggs having been found in the nests of _Turdus mustelinus_ and _T. fuscescens_, _Sturnella magna_ and _S. neglecta_. In each instance they had been incubated. How the young Cowbird generally fares when hatched in the nests of birds of equal or larger size, and the fate of the foster-nurslings, is an interesting subject for investigation. Mr. J. A. Allen saw, in Western Iowa, a female _Harporhynchus rufus_ feeding a nearly full grown Cowbird,—a very interesting fact, and the only evidence we now have that these birds are reared by birds of superior size. It lays also in the nests of the common Catbird, but the egg never remains there long after the owner of the nest becomes aware of the intrusion. The list of the birds in whose nests the Cow Blackbird deposits her egg and it is reared is very large. The most common nurses of these foundlings in New England are _Spizella socialis_, _Empidonax minimus_, _Geothlypis trichas_, and all our eastern _Vireos_, namely, _olivaceus_, _solitarius_, _noveboracensis_, _gilvus_, and _flavifrons_. Besides these, I have found their eggs in the nests of _Polioptila cærulea_, _Mniotilta varia_, _Helminthophaga ruficapilla_, _Dendroica virens_, _D. blackburniæ_, _D. pennsylvanica_ and _D. discolor_, _Seiurus aurocapillus_, _Setophaga ruticilla_, _Cyanospiza cyanea_, _Contopus virens_, etc. I have also known of their eggs having been found in the nests of _Vireo belli_ and _V. pusillus_, and _Cyanospiza amœna_. Dr. Cooper has found their egg in the nest of _Icteria virens_; and Mr. T. H. Jackson of West Chester, Penn., in those of _Empidonax acadicus_ and _Pyranga rubra_.