Birds, as a rule, use a great deal of care and thought in the location of their nests. After they have selected a certain grove or field as the one best suited to their purposes, or as the one around which cluster the happiest memories, it usually requires several days of flying and peeping about, of spying and exploration, before the exact spot for the precious domicile is finally settled upon. It is a delicate matter for many birds, for security from sun, storm, and enemies must all be taken into account. Old birds, as has been frequently observed, build better nests and select more clever locations for their nests than the young and inexperienced. The nest-building habits of many birds are known to have changed during the past few hundred years. The American house-swallow did most certainly not build under the eaves of human houses 300 years ago, nor did the hair-bird in her nest with horsehair as she invariably does now. The fact that wrens, swifts, and martins now build almost altogether in boxes and chimneys shows that birds are able and willing to adapt themselves to new conditions. The chimney-swift and purple martin, it is said, still cling to their aboriginal custom of rearing their young in hollow trees in the unsettled parts of America. The indomitable house-sparrow builds its nest almost anywhere, from knot-holes and tin cans to electric-light globes and tree-tops. Its original dwelling was probably an arboreal affair, like that of other sparrows, and different nesting-places have been adopted as a result of its association with man. Not only in its architecture, but in several other ways, this bird has departed from the traditions of its tribe. The Fringillidae (the sparrow family of birds) are seed-eaters, both in structure and practice. But the house-sparrow, since it left the fields and groves to become a gamin on human streets, has learned to eat almost anything, and one thing, too, about as cheerfully as another. The varied habits of this bird are probably due to its natural elasticity in the first place, supplemented by the unsettling influences of its rather kaleidoscopic experiences during the past few hundred years.