lement of
eggs by the builders themselves.

Even after the youngsters have left the nest the mother cowbird does
not assume the care of them, but still leaves them in charge of the
foster parents. It is laughable, almost pathetic, to see a tiny
oven-bird or redstart feeding a strapping young cowbird which is
several times as large as herself. She looks like a pigmy feeding a
giant. In order to thrust a tidbit into his mouth she must often stand
on her tiptoes. Why the diminutive caterer does not see through the
fraud I can not say. She really seems to be attached to the hulking
youngster. By and by, however, when he grows large enough to shift for
himself, he deserts his little parents and nurses and seeks
companionship among his own blood kindred, who doubtless bring him up
in the way all cowbirds should go.

It is surprising how many species are imposed on successfully by the
cowbird. The number, so far as has been observed, is ninety, with
probably more to be added. Among the birds most frequently victimized
are the phoebes, the song sparrows, the indigo birds, the bush
sparrows, and the yellow-breasted chats. Even the nests of the
red-headed woodpecker and the rock wrens are not exempt. Some species,
notably the summer warblers, detect the imposture and set about
defeating the purposes of the interloper by building another story to
their little cottage, leaving the obtruded eggs in the cellar, where
they do not receive enough warmth to develop the embryo.

While it is surprising that acute birds should allow themselves to be
imposed on in this way, perhaps, after all, they look upon the cowbird
as a kind of blessing in disguise; at least, he may not be an unmixed
evil. They may act on the principle of reciprocity--that "one good
turn deserves another." What I mean is this: In my rambles I have
often found the cowbirds the first to give warning of the approach of a
supposed danger. Having no domestic duties of their own, they can well
secrete themselves in a tall tree overlooking the entire premises, and
thus play the useful role of sentinel. This, I am disposed to believe,
is one of the compensating uses of this parasite, and may furnish the
reason for his being tolerated in birdland. And he is tolerated. Has
any one ever seen other birds driving the cowbird away from their
breeding precincts, or charging him with desperate courage, as they do
the blue jays, the hawks, the owls, and other predator