The most of our bird books have the earmarks of the library. An author may be familiar with a few birds studied afield, but the greater number are studied in the library. Take the cowbird as an example. One author after another rings in the same old chestnut about the disreputable bird that lays its eggs in other birds' nests and deserts its offspring. These authors wind up by calling attention to the wonderful instinct that causes the young cowbird to desert its foster-parents to associate with its kind. I will say now, that long before I had the opportunity to study the bird, I did not believe it possible for a young bird, by its own knowledge, to hunt up and associate with birds of its kind. That would be a miracle, and the days of miracles are passed. In my study of birds I have found that old birds educate the young, and I knew that the young cowbird was piloted by its mother, or the foster-parents turned it over to its kind to be rid of incumbrances. Few writers have studied the cowbird through the nesting season. Mr. John Burroughs writes that he found small eggs in the path that had two pricks in the shell. Afterward he detected the cowbird removing an egg from a bird's nest. Mr. Burroughs intimates that the cowbird did this to deceive the owners of the nest. They, finding the proper number of eggs, would not detect the fraud. I was sincerely grieved that a delightful writer on natural history should make such a break. His interpretation would endow the cowbird with a keen reasoning power, and would make chumps of the others; too senseless to know their own eggs. In my observations, when the victimized birds return and find the alien egg, they exhibit great distress.
BLUE-WINGED YELLOW WARBLER.
My first study of the cowbird happened in an unexpected manner. I was watching the nest of a pair of yellow warblers (Dendroica æstiva) that contained two eggs. While the owners were absent I saw a cowbird flutter on to the nest and add her parasite egg to its contents. When the yellowbirds returned they at once discovered what had taken place, and acted as if wild with alarm and distress. For a half-hour the birds flew wildly about, uttering plaintive cries, after which they settled down on a twig, where they could overlook the nest. They now seemed less excited, and were evidently holding a consultation. After awhile they seemed to agree on a course of action, for the female went on to the nest and the male bird tried to sing away the trouble, but I thought his song less earnest than usual.
No more eggs were laid, which was somewhat remarkable, as the yellowbird's number is usually four.
I found the young cowbird hatched out just twelve days after the egg was laid. The next morning I found the two yellowbirds out of the shell. When the cowbird was two days old he crowded both the little birds out of the nest. When I found them, one was dead and the other gasping as if fatally hurt. While I was watching the latter, the mother-bird appeared with an insect. She offered the food to the dying bird, and appeared greatly troubled when it was not received. After awhile she seemed to comprehend that the little one could not eat, and she fed the insect to the cowbird. Before flying away, she returned to the gasping bird, and looked at it by turning her head from side to side, while she uttered a succession of low, plaintive notes.
After this, both yellowbirds had all they could do to supply the black giant with food. When he was old enough to fly, or, at least, was completely feathered, his foster-parents coaxed him out of the nest after the manner of all bird-kind. Birds know when their young are old enough to leave the nest, and withhold food until the little ones are downright hungry, and then tempt them out with a dainty morsel. While tempting the young cowbird from the nest, the yellowbirds made as much effort and appeared as joyous when successful as if the labor had been performed for their own bright-eyed, pretty birdlings.
The young cowbird, when once out, did not return to the nest for shelter. His growing appetite taxed the strength of both birds to the utmost. Every moment of daylight was occupied in catering to his wants. One day I missed the female yellowbird, and, after a long search, found her engaged in building a new nest. She had forsaken her former charge.