The warblers and smaller flycatchers are generally the sufferers,
though I sometimes see the slate-colored snowbird unconsciously
duped in like manner; and the other day, in a tall tree in the
woods, I discovered the black-throated green-backed warbler devoting
itself to this dusky, overgrown foundling. An old farmer to whom I
pointed out the fact was much surprised that such things should
happen in his woods without his knowledge.

These birds may be seen prowling through all parts of the woods at
this season, watching for an opportunity to steal their egg into
some nest. One day while sitting on a log I saw one moving by short
flights through the trees and gradually nearing the ground. Its
movements were hurried and stealthy. About fifty yards from me it
disappeared behind some low brush, and had evidently alighted upon
the ground.

After waiting a few moments I cautiously walked in the direction.
When about halfway I accidentally made a slight noise, when the bird
flew up, and seeing me, hurried off out of the woods. Arrived at the
place, I found a simple nest of dry grass and leaves partially
concealed under a prostrate branch. I took it to be the nest of a
sparrow. There were three eggs in the nest, and one lying about a
foot below it as if it had been rolled out, as of course it had. It
suggested the thought that perhaps, when the cowbird finds the full
complement of eggs in a nest, it throws out one and deposits its own
instead. I revisited the nest a few days afterward and found an egg
again cast out, but none had been put in its place. The nest had
been abandoned by its owner and the eggs were stale.

In all cases where I have found this egg, I have observed both male