Page:Popular Science Monthly Volume 6.djvu/500

484 energetic than its parents, and this, joined with the fact that the bird's mate may have been reared in a nest of perfect construction, of itself would tend to remedy, in part, the defects its partner might allow; these facts together would certainly secure an approach to, if not the complete attainment of, a "typical" robin's nest. So, as the years roll by, the nest of the robin would remain substantially the same, while the amount of variation that now exists would be perpetuated, and probably very slowly increased.

Why indeed, a robin should line its nest with mud, and a cat-bird should not, is probably past finding out, but, as changes gradually brought about by man's agency have already effected changes in the habits of some of our birds, so these same changes, ever in progress in the haunts of our robin, may cause these birds to gradually omit this lining of mud in their nests, and so make them more like the nests of other thrushes; just as the cliff-swallow, with us, no longer places a "bottle-neck" opening to its mud-built nests. There is an instability in the whole range of the habits of birds, going hand-in-hand with the undoubted tendency to variation in their anatomical details. Natural selection, or whatever may be the governing impulse that controls it, also indirectly causes the range of variation in the details of the construction of their nests, inasmuch as these variations of habit are the necessary result of changes wrought in the physical construction of the creatures themselves, for, stripped of the haze that metaphysics has gathered about it, as a bewildering gloom, we can see in the operations of the mind, in man and bird, only the curious results of the workings of those fatty atoms, intimately combined, we call the brain; and no argumentation can separate this brain and mind. They are just as interdependent, and parts of a single whole, as the eye and sight, the nose and smell, hearing and the ear, the circulation of the blood and the beating of our hearts.

A nest of totally different character, that of the well-known Baltimore oriole (Icterus Baltimore), was more carefully studied by the writer, inasmuch as it afforded more marked variations from what may be considered a "typical" form of the structure.

Mr. Wallace has shown that, where a nest is so constructed as to conceal the sitting bird, in all such cases, the birds are of bright, showy plumage, and would be easily detected by birds of prey, if not concealed when occupying their nests. Of the family Icteridæ, to which our Baltimore oriole belongs, Mr. Wallace says, "The red or yellow-and-black plumage of most of these birds is very conspicuous, and is exactly alike in both sexes. (This is not true of the Baltimore oriole, the female of which is much less brightly colored.) They are celebrated for their fine, purse-shaped, pensile nests." There are now two considerations worthy of attention, with reference to this bird