But what kind of nests do the rock nuthatches construct on their limestone walls? That is one of the most interesting features of the life of these birds. One writer[1] who has observed them in their native haunts describes the rock nuthatch as "an expert clay mixer and molder." The bird does not chisel out a nursery in the rock--no, indeed; his method of constructing his nest is as follows: Having found a little hollow or indentation on the rocky wall, he will erect a cap or dome of mortar over it, plastering the structure so firmly against the surface that no rain or storm or predaceous creeping thing can demolish it until long after it has been abandoned by the little architect. The circular base of the nest is ten or twelve inches in diameter. The dome is not entirely closed up, but a small orifice is left in the center, upon the edges of which a narrow neck or funnel, also made of mortar, is raised, the hole just large enough to admit the body of the bird. The funnel is about three inches long. The building material employed is fine clay softened and glutinated with the bird's saliva and mixed with plant fibers, for the little mason does not believe in making bricks without straw. So well packed is the inch-thick wall that a stiff knife blade must be used to cut through it. While the natural color of the adobe cottage is ash-gray, and therefore harmonizes with the general hue of its surroundings, and also with the mezzotints of the builder, yet he sometimes decorates it with the gaily colored wings of moths caught in the chase and attached to the plaster while it is fresh. The rock nuthatch is as expert a mixer of mortar as the well-known cliff swallows of our own country, and his adobe dwellings bear a close resemblance to theirs. 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. A FEATHERED PARASITE* *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.