The method of building, of course, varies as much as the patterns of nests. Even when the same materials are used, they are differently treated, and a nest of sticks only may in one case be merely thrown together, as it were, while in another they are so carefully interlaced that the structure is a basket, and holds together if held by the rim only. Another, the same in general appearance, would immediately fall to pieces if similarly treated. A reason for this is discoverable in some cases, but not in all. If we examine a great many nests, the rule will hold good, I think, that where they are very loosely put together, the locality is such that no natural disturbing causes, as high winds, are likely to bring disaster. Until I studied this point the occurrence of exceedingly frail nests was ever a matter of surprise, for it is to be remembered that the same species, as a cat-bird or cardinal red-bird, does not build after a uniform fashion, but adapts its work to the spot chosen for the nest. It would be very hazardous to say that a nest was built by this or that bird, unless the builder was seen in possession. So difficult is it to watch a pair of birds while building, that the method of their working is largely to be guessed at from the work itself, but by means of a field-glass a good deal can be learned. It would appear as if a great many twigs were brought for the foundation of a nest, such as a cat-bird’s or song-sparrow’s, that were unsuitable. I have occasionally seen a twig tossed aside with a flirt of the head very suggestive of disappointment. The builders do not always carry with them a distinct idea of what they want when hunting for material, and so labor more than would be necessary if a little wiser. Very funny disputes, too, often arise, and these are most frequent when wrens are finishing their huge structures in a box or some corner of an out-building. A feather, or a bit of thread, or a small rag will be carried in by one bird and tossed out by the other with a deal of scolding and “loud words” that is positively startling. But when the framework of any ordinary open or cup-shaped nest is finally completed, the lining is not so difficult a matter. Soft or yielding materials are used that to a greater or less extent have a “felting property,” and by the bird’s weight alone assume the shape desired. This is facilitated by the bird in two ways: the builder sits down, as if the eggs were already laid, and with its beak pushes the loose material between it and the framework, and tucks odd bits into any too open crevices. While doing this, it slowly moves around until it has described a complete circle. This brings to light any defects in the outer structure, and the bird can often be seen tugging away at some projecting end, or its mate, outside of the nest, rearranging a twig here and there, while the other bird—shall I say?—is giving directions.