The cowbird mother does not build a nest for her little family.
The cowbird's tactics are probably to watch the movements of the parent bird.
When they find a cowbird's egg in their nest, they go away and leave it there, and make a new nest.
Every cowbird is reared at the expense of two or more song-birds.
Eggs occasionally disappear from the nest prior to or during incubation, without subsequent addition of cowbird eggs.
One of these is called the Argentine cowbird (Molothrus bonariensis).
So it is, my boy; but the cowbird is one of the exceptions I told you about; and I am glad to say there are very few.
Despite this fact the cowbird's eggs are often first to hatch.
The Bell Vireo does abandon the nest when all but one of its own eggs have been removed by the cowbird.
It is little wonder that discerning people are not fond of the cowbird.