Bird lore - Project Puffin

The Chestnut-Sided Warbler 131
"As the young birds began to grow, the Cowbird not only maintained, but
rapidly increased its lead over its small nest-mate. At every visit of the parent
bird with food, its capacious gullet could be seen violently waving aloft and
almost completely hiding the feeble little mouth of the Warbler, whose owner
was pathetically doing its best in a dumb appeal for food. The Cowbird's
appetite seemed never to be satiated and, unlike most nestlings, which relapse
after a meal and give their brethren the next chance, he seemed ready for every
fresh opportunity; and, by reason of his superior display, he usually succeeded
in obtaining the coveted morsel. However, the young Warbler did manage to
get an occasional portion, and I had strong hopes that he might reach maturity.
For I realized that a Chestnut-sided Warbler's usual laying is about five eggs,
and that therefore some four eggs must have been made to give place to the
two Cowbird's. Hence the young Cowbird in the nest might reasonably be
granted the room and food of four young Warblers. More than this I hoped
he was not getting.
"On July 18, at 3.30 p.m., when the birds were about four days old, I took
them from the nest to compare their sizes. I replaced them in the nest, but
that was the last I saw of the poor little Warbler. When I returned at 5 p.m.,
the Cowbird was in sole and triumphant possession of the nest. Just what
became of the Chestnut-sided Warbler will never be known, but my theory is
that, weakened by lack of sufficient food, the little fellow at last became too
feeble to raise himself at all, and was crushed to death by the Cowbird's gross
body. The parent birds, returning and finding the little corpse in the bottom
of the nest, were no doubt impelled by their instinctive sense of cleanhness to
carry it to a distance; for the most careful search over a large area beneath the
nest failed to reveal any sign of the missing bird, thus proving that it had not
fallen from the nest nor been forced out by the Cowbird.
"The Cowbird now had things all his own way and, there being no one to
dispute his right to all the food, he grew with amazing rapidity. The dainty
little cup of a nest, never built to accommodate such a monster, was soon com-
pletely forced out of shape. His body then protruded beyond the lower rim of
the nest, and the ground underneath became littered with droppings, quite
bafihng the cleanly, sanitary instincts of the Warblers.
"The Cowbird, now almost twice as large as his devoted foster-parents,
rises with hideous chitterings of delight to receive an ever-acceptable meal.
I visited the nest at 7.30 a.m., on July 26. As I walked home to breakfast, I
resolved that in the interests of justice I ought to put an end to that Cowbird,
as a murderer and a menace to the welfare of birddom. But when I
returned to the spot, about 9 a.m., he had escaped me; the nest was empty,
my bird flown. No doubt, if I had searched and listened, I should have
heard him shouting for food not far away; but my spirit of vengeance was
only half-hearted at best, and so I left him, a criminal abroad, to be the parent,
I suppose, of others as bad."