Dropping the eggs on the ground might entail a deliberate waste, as we know of no reason why the bird should suppose that they would be hatched and the young reared, if scattered broadcast over the country. On the other hand, this might merely indicate that the birds had found no suitable place in which to deposit their eggs. The form of waste caused by the birds laying in old, disused nests, or by laying such a large number of eggs in a single nest that it is impossible for the rightful owner to incubate them and rear the young, can hardly be said to be deliberate, as it is doubtless caused by a lack of intelligence; if the bird designedly scatters its eggs broadcast on the ground, it is wantonly wasteful; if it merely lays in disused nests, or overcrowds nests actually occupied, the bird may simply be stupid. It would be impossible to say what per cent of eggs laid by this species of cowbird is wasted. Hudson estimates that each female lays from sixty to one hundred eggs in a single season, and it does not seem to me that this statement is an exaggeration. One female which I dissected had laid three eggs within the few preceding days, and a fourth was almost ready to be deposited. The bird which suffers most from the parasitic habits of the cowbird in the vicinity of Rosario de Lerma, is the oven-bird (_Furnarius rufus_); however, of the great number of eggs laid in the nests of the above-named species, our observations tend to show that the greater part are lost. Among the scores of oven-bird nests which we examined, only two were still occupied by the owners, the desertion being apparently due to the invasion of the cowbirds. So persecuted were the oven-birds that it is difficult to understand how any of them survived in this immediate locality. The nests were common enough, it being not unusual to find several of them in a single tree, but the birds themselves were not abundant. It is possible that some of the pairs may have built several nests each in their vain attempts to escape the attentions of the cowbirds. In no instance had the walls or top of the oven-birds’ nests been broken or perforated in any manner, in order that light could penetrate to the interior; they were not tampered with in any way, and the cowbirds seemed content to use them just as the oven-birds had constructed them. I believe that the greater number of _M. b. bonariensis_ that reach maturity are reared by the smaller birds, such as finches, warblers, and vireos, in whose nests only a few eggs are laid, which increases the favorable chances of their incubation. Also, the larger and heavier eggs of the cowbird frequently crush at least a part of the smaller eggs which naturally have a more fragile shell, thus forestalling to a marked degree the competition that might arise between the young birds in the nest.