The remaining seven nests were in a mixed tangle of Virginia creeper and grape-vine. These seven nests were all at a greater elevation than any I found in smilax or other thorn-bearing growths; one nest being thirteen feet from the ground.
These bush-retreats of the mice were all distinctly globular, or globoid, with the entrance usually near the rim of the original structure, and looking downward. These original structures were not merely covered at the top, but distinctly arched over; and the exterior often had a "pulled-to-pieces" appearance that suggested a chance accumulation of twigs and dead leaves, rather than designed.
A careful examination convinced me that twenty-nine were nests of cat-birds, cardinal-grosbeaks, or song-thrushes, and two were nests of the robin; all of which had been built by these birds in May or June of the same year—five or six months previously. The nests of the robin are apparently less popular, on account of the partial or complete mud-lining.
In this series of twenty-nine nests I determined that the foundations and lower portion of the sides, for about one half their extent, were unaltered to any significant extent; and many appeared as if a smaller bird's nest had been bodily removed, inverted, and so used as a roof to the lower structure. Whether the rougher exterior, to which I have alluded, was due to expoure since early summer, to unskillful work on the part of the mice, or a design of these mammals to render the nests less conspicuous, could, of course, not be determined.
Eight of the series were to me quite unlike birds' nests in their construction. The interlacing of the twigs was not like the ordinary work of birds; and the internal capacity of each one of this series was much smaller than that of an ordinary cat-bird's nest; while the exterior measurements were the same or nearly so—thus showing great difference in the thickness of the walls of the structure.
Three of these eight nests I picked to pieces, and the lining proved to be a mass of downy feathers—how they got them is a mystery—and an abundance of the "silk" of the milkweed; this being a material not used by any of the birds I have named, and indeed not ready for use until after bird-nesting is over.
Still, I am not yet prepared to make an ex-cathedra statement that these mice do build bird-nest-like structures in smilax and other dense growths, without having at least the base of a bird's nest as a starting-point; yet, why they should not, does not readily appear, when we remember that they build beautifully designed nests in hollow logs, tufts of grass, and under flat stones. Such nests are their ordinary summer homes.
It is certain that the materials for these summer nests, which, as a rule, are on or very near the ground, are often carried from quite distant points; so, why should they not carry them up a few feet into tangled growths, offering almost as sure a footing as the ground itself?
