| Wing | tail | culmen | tarsus | |
| Largest. (11,271, ♂, Fort Bridger.) | 4.60; | 3.35; | .72; | 1.03. |
Smallest. (17,297, ♂, Mira Flores, L. C.) | 3.80; | 2.65; | .60; | .84. |
Habits. The common Cow Blackbird has a very extended distribution from the Atlantic to California, and from Texas to Canada, and probably to regions still farther north. They have not been traced to the Pacific coast, though abundant on that of the Atlantic. Dr. Cooper thinks that a few winter in the Colorado Valley, and probably also in the San Joaquin Valley.
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.
Usually not more than a single Cowbird’s egg is found in the same nest, though it is not uncommon to find two; and in a few instances three and even four eggs have been met with. In one instance Mr. Trippe mentions having found in the nest of a Black and White Creeper, besides three eggs of the owner of the nest, no less than five of the parasite. Mr. H. S. Rodney reports having found, in Potsdam, N. Y., May 15, 1868, a nest of Zonotrichia leucophrys of two stories, in one of which was buried a Cowbird’s egg, and in the upper there were two more of the same, with three eggs of the rightful owners. In the spring of 1869 the same gentleman found a nest of the Sayornis fuscus with three Cowbird’s eggs and three of her own.
Mr. Vickary, of Lynn, found, in the spring of 1860, the nest of a Seiurus aurocapillus, in which, with only one egg of the rightful owner, there were no less than four of the Cowbird. All five eggs were perfectly fresh, and had not been set upon. In the summer of the preceding year the same gentleman found a nest of the Red-eyed Vireo containing three eggs of the Vireo and four of the Cow Blackbird.
How the offspring from these eggs may all fare when more than one of these voracious nurslings are hatched in the same nest, is an interesting problem, well worthy the attention of some patiently inquiring naturalist to solve.
The Cow Blackbird appears in New England with a varying degree of promptness, sometimes as early as the latter part of March, and as frequently not until the middle of April. Nuttall states that none are seen in Massachusetts after the middle of June until the following October, and Allen, that they are there all the summer. My own observations do not correspond with the statement of either of these gentlemen. They certainly do become quite rare in the eastern part of that State after the third week in June, but that all the females are not gone is proved by the constant finding of freshly laid eggs up to July 1. I have never been able to find a Cow Blackbird in Eastern Massachusetts between the first of July and the middle of September. This I attribute to the absence of sufficient food. In the Cambridge marshes they remain until all the seeds have been consumed, and only reappear when the new crop is edible.