It is interesting to note that the European nuthatch, while nesting regularly in tree cavities, sometimes also chooses the crannies of rocks, when he goes a little more extensively into the plastering business; but his skill is not so well developed as that of his oriental cousin, whose mud cottage is a model of its kind.
[1] The writer referred to is Mr. H. C. Tracy, to whose charming article in "The Wilson Bulletin," published at Oberlin, Ohio, I am indebted for all my material on the rock nuthatch.
*Reprinted from Appleton's "Popular Science Monthly," with additions.
Nothing could more clearly prove that a common law runs through the whole domain of Nature than the fact that in every division of her realm there seems to be a class of parasites. In the vegetable world, as is well known, there are various plants that depend wholly on other plants for the supply of their vital forces. And in the human sphere there are parasites in a very real and literal sense--men and women who rely upon the toil and thrift of others to sustain them in worthless idleness.
In view of the almost universal character of this law it would be strange if these peculiar forms of dependence did not appear in the avian community. We do find such developments in that department of creation. Across the waters there is one bird that has won an unenviable reputation as a parasite: the European cuckoo relies almost wholly on the efforts of its more thrifty neighbors to hatch and rear its young, and thereby perpetuate the species. Strangely enough, our American cuckoos are not given to such slovenly habits, but build their own nests and faithfully perform the duties of nidification, as all respectable feathered folk should. However, this parasitical habit breaks out, quite unexpectedly, it must be conceded, in another American family of birds entirely distinct from the cuckoo group.
In America the cowbird, often called the cow bunting, is the only member of the avian household that spirits its eggs into the nests of other birds. The theory of evolution can do little toward accounting for the anomaly, and even if it should venture upon some suggestions it would still be just as difficult to explain the cause of the evolution in this special group, while all other avian groups follow the law of thrift and self-reliance.