The Yellow Warbler
Jonathan Swift's epitome of the subject, if not specifically true, is at least correct in its general application:
ad infinitumEven the tiny egg of a butterfly has its ichneumon parasite, a microscopic wasp, which lays its own egg within the larger one, which ultimately hatches a wasp instead of the baby caterpillar.
But who ever heard of anything but good luck falling to the lot of cow-bird or cuckoo, except as its blighting course is occasionally arrested by the outraged human? They always find a feathered nest.
In this connection it is interesting to note certain developments in bird life upon the lines of which evolution might work with revolutionary effect. Most of our birds are helpless and generally resigned victims to the cow-bird, but there are indications of occasional effective protest among them. Thus the little Maryland yellow-throat, according to various authorities, often ousts the intruded egg, and its broken remains are also occasionally seen on the ground beneath the nests of the cat-bird and the oriole. The red-eyed vireo, on the other hand, though having apparently an easier task than the latter, in the lesser depth of her pensile nest, commonly abandons it altogether to the unwelcome speckled ovum—always, I believe, if the cow-bird has anticipated her own first egg.
A Blighted Home
But we have a more remarkable example of opposition in the resource of the little yellow warbler, which I have noted as one of the favorite dupes of the cow-bird—a deliberate, intelligent, courageous defiance and frequent victory which are unique in bird history, and which, if through evolutionary process they became the fashion in featherdom, would put the cow-bird's mischief greatly at a discount. The identity of this pretty little warbler is certainly familiar to most observant country dwellers, even if unknown by name, though its golden-yellow plumage faintly streaked with dusky brown upon the breast would naturally suggest its popular title of "summer yellow-bird." It is one of the commonest of the mnio-tiltidæ, or wood-warblers, though more properly a bird of the copse and shrubbery than of the woods.
The Normal Nest of the Yellow Warbler
This nest is a beautiful piece of bird architecture. In a walk in search of one only a day or two ago I procured one, which is now before me. It was built in the fork of an elder-bush, to which it was moored by strips of fine bark and cobweb, its downy bulk being composed by a fitted mass of fine grass, willow cotton, fern wood, and other similar ingredients. It is about three inches in depth, outside measurement. But this depth greatly varies in different specimens. Our next specimen may afford quite a contrast, for the yellow warbler occasionally finds it to her interest to extend the elevation of her dwelling to a remarkable height. On page 50 is shown one of these nests, snugly moored in the fork of a scrub apple-tree. Its depth from the rim to the base, viewed from the outside, is about five inches, at least two inches longer than necessity would seem to require, and apparently with a great waste of material in the lower portion, as the hollow with the pretty spotted eggs is of only the ordinary depth of about two inches, thus hardly reaching half-way to the base. Let us examine it closely. There certainly is a suspicious line or division across its upper portion, about an inch below the rim, and extending more or less distinctly completely around the nest. By a very little persuasion with our finger-tip the division readily yields, and we discover the summit of the nest to be a mere rim—a top story, as it were—with a full-sized nest beneath it as a foundation. Has our warbler, then, come back to his last year's home and fitted it up anew for this summer's brood? Such would be a natural supposition, did we not see that the foundation is as fresh in material as the summit. Perhaps, then, the bird has already raised her first spring brood, and has simply extended her May domicile, and provided a new nursery for a second family. But either supposition is quickly dispelled as we further examine the nest; for in separating the upper compartment we have just caught a glimpse of what was, perhaps only yesterday, the hollow of a perfect nest; and, what is more to the point of my story, the hollow contains an egg—perhaps two, in which case they will be very dissimilar, one of delicate white with faint spots of brown on its larger end, the putting of the warbler, the other much larger, with its greenish surface entirely speckled with brown, and which, if we have had any experience in bird-nesting, we immediately recognize as the mischievous token of the cow-bird. We have discovered a most interesting curiosity for our natural-history cabinet—the embodiment of a presumably new form of intelligence in the divine plan looking to the survival of the fittest. It is not known how many years or centuries it has taken the little warbler to develop this clever resource to outwit the cow-bird. It is certain, however, that the little mother has got tired of being thus imposed upon, and is the first of her kind on record which has taken these peculiar measures for rising above her besetting trouble.
The Yellow Warbler at Home
A Suspicious Nest of the Yellow Warbler
Who can tell what the future may develop in the nests of other birds whose homes are similarly invaded? I doubt not that this crying cow-bird and cuckoo evil comes up as a matter of consideration in bird councils. The two-storied nest may yet become the fashion in featherdom, in which case the cow-bird and European cuckoo would be forced to build nests of their own or perish.
But have we fully examined this nest of our yellow warbler? Even now the lower section seems more bulky than the normal nest should be. Can we not trace still another faint outline of a transverse division in the fabric, about an inch below the one already separated? Yes; it parts easily with a little disentangling of the fibres, and another spotted egg is seen within. A three-storied nest! A nest full of stories—certainly. I recently read of a specimen containing four stories, upon the top of which downy pile the little warbler sat like Patience on a monument, presumably smiling at the discomfiture of the outwitted cow-bird parasite, who had thus exhausted her powers of mischief for the season, and doubtless convinced herself of the folly of "putting all her eggs in one basket."
The Nest Separated
When we consider the life of the cow-bird, how suggestive is this spectacle which we may see every year in September in the chuckling flocks massing for their migration, occasionally fairly blackening the trees as with a mildew, each one the visible witness of a double or quadruple cold-blooded murder, each the grim substitute for a whole annihilated singing family of song-sparrow, warbler, or thrush! What a blessing, at least humanly speaking, could the epicurean population en route in the annual Southern passage of this dark throng only learn what a surpassing substitute they would prove—on toast—for the bobolinks which as "reed-birds" are sacrificed by the thousands to the delectable satisfaction of those "fine-mouthed and daintie wantons who set such store by their tooth"!
And what the cow-bird is, so is the Continental "cuckoo." Shall we not discriminate in our employment of the superlative? What of the throstle and the lark? Shall we still sing—all together: