Wonderful as the instinct of migration seems, it is not, perhaps, so altogether amazing in itself as in some of its attendant details. To a great extent, birds follow the opening foliage northward, and flee from its fading, south; they must keep near the food on which they live, and secure due shelter for their eggs. Our earliest visitors shrink from trusting the bare trees with their nests; the Song-Sparrow seeks the ground; the Blue-Bird finds a box or a hole somewhere; the Red-Wing haunts the marshy thickets, safer in spring than at any other season; and even the sociable Robin prefers a pine-tree to an apple-tree, if resolved to begin housekeeping prematurely. The movements of birds are chiefly timed by the advance of vegetation; and the thing most thoroughly surprising about them is not the general fact of the change of latitude, but their accuracy in hitting the precise locality. That the same Cat-Bird should find its way back, every spring, to almost the same branch of yonder larch-tree,--that is the thing astonishing to me. In England, a lame Redstart was observed in the same garden for sixteen successive years; and the astonishing precision of course which enables some birds of small size to fly from Australia to New Zealand in a day--probably the longest single flight ever taken--is only a part of the same mysterious instinct of direction. In comparing modes of flight, the most surprising, of course, is that of the Swallow tribe, remarkable not merely for its velocity, but for the amazing boldness and instantaneousness of the angles it makes; so that eminent European mechanicians have speculated in vain upon the methods used in its locomotion, and prizes have been offered, by mechanical exhibitions, to him who could best explain it. With impetuous dash, they sweep through our perilous streets, these wild hunters of the air, "so near, and yet so far"; they bathe flying, and flying they feed their young. In my immediate vicinity, the Chimney-Swallow is not now common, nor the Sand-Swallow; but the Cliff-Swallow, that strange emigrant from the Far West, the Barn-Swallow, and the white-breasted species, are abundant, together with the Purple Martin. I know no prettier sight than a bevy of these bright little creatures, met from a dozen different farm-houses to picnic at a way-side pool, splashing and fluttering, with their long wings expanded like butterflies, keeping poised by a constant hovering motion, just tilting upon their feet, which scarcely touch the moist ground. You will seldom see them actually perch on anything less airy than some telegraphic wire; but, when they do alight, each will make chatter enough for a dozen, as if all the rushing hurry of the wings had passed into the tongue.