It is common to say that these occasional winter Swallows are the later broods of young, which, being too infantile to migrate, are compelled to linger in the country of their nativity, and becoming lethargic from the advancing cold, at length die before the spring. But when this hypothesis is looked at, it seems hardly tenable. In many of the instances recorded, the specimens seen even late into the winter, are represented as gaily and vigorously hawking for flies, or sweeping over the water as in summer. This does not look like poor deserted orphans starved with the cold, retiring to die; but birds in health, temporarily awakened from normal slumber by an unusual temperature, and instantly ready for a full use of their faculties. However, to settle the point by fact, Mr Bell distinctly states that his specimen of December 10th was "an adult bird, _not_ a young bird of the season." If it should be asked why they do not appear in January or February, as well as November and December, the answer is obvious. The winter's lethargy of hybernating warm-blooded vertebrates is much more readily interrupted in the earlier part of the season than in the middle and latter part. And this is natural; for the more intense cold of January benumbs and suspends the vital functions far more completely, and the _coma_ so superinduced is sufficiently deep to resist the counteracting influence of a few warm days, even though the temperature should be as high as on those earlier days that awakened them, or even higher. The aggregate evidence, then, seems to leave no room for reasonable doubt, that a certain number of our _Hirundinidæ_,--few, indeed, as compared with the vast migrant population, but still considerable, looked at _per se_,--for some reason or other, evade the task of a southward flight, and remain, becoming torpid, occasionally betrayed into a temporary activity, and resuming their active life, about the same time, or occasionally a little _before_ the time, of the arrival of their congeners from abroad. It is, however, desirable for the absolute settlement of the question, that specimens, actually discovered in a lethargic condition, should come under the observation of competent scientific naturalists, _open to conviction_, who would leave them _in situ_, keeping an eye on them from time to time till the return of warm weather in spring. It is not enough to take them into a warm room, and to shew that they revive in such circumstances: we want to know positively whether they will be resuscitated normally and naturally by the vernal warmth, and come forth spontaneously to sport, and wheel, and skim, and soar, and stoop, and hawk, and twitter,--among their travelled fellows. Who will undertake to decide the point in this manner? He will have achieved a name in science. [113] _Phys. Theol._, vii., Note _d_. [114] _Règne Anim._, (Griffith's Ed.,) vii. 61. [115] _Phil. Trans._, 1763. [116] _Letter_ x.