With what astonishing sight must not the kestrel be gifted to perform such a feat! It is difficult enough for a human being to watch a square yard of ground so carefully that a field-vole shall be seen as it glides among the grass. How wonderful, therefore, must be the powers of vision which enable the bird to watch a large field, to detect from that height the little, dusky animal, and pounce down upon it with unerring swoop! How astonishing must be the optical mechanism of those eyes which at so great a distance from the prey can act like telescopes, and yet can alter their range so rapidly that in the few seconds which are consumed in making the stoop, they have accommodated themselves to an entirely different focus. In his “At Last,” C. Kingsley mentions that in passing through a tropical forest the traveller is frequently checked by some creeper which hangs in the path, and which is not seen because the eye cannot focus itself with sufficient rapidity. Yet the traveller is only proceeding at a walking pace, whereas the stoop of the kestrel on its prey is swift as the fall of a stone through the air, and in a second or two the eye has to accommodate itself from a range of many yards to that of a few inches. The value of the kestrel in keeping down the numbers of the field-vole, and so aiding in preserving the balance of Nature, can hardly be over-estimated. There have been cases where the field-voles had increased to such a degree that pitfalls had to be dug for their capture, and they had to be destroyed artificially, because the kestrels and other predacious birds and animals had been almost extirpated. Other enemies to agriculture are also destroyed by the kestrel. Mr. Johns mentions an instance where the stomach of a kestrel was opened, and was found to contain, beside a field-vole, nearly eighty caterpillars, twenty-four beetles, and a leech! Now, we will return to our field-vole. Like the squirrel and several other rodents, it makes two nests, one for the winter and the other for the summer. The winter nest is mostly made at some distance from water, is formed at the end of a burrow, and seldom reaches more than a few inches below the surface of the ground. It is to this winter nest that the poet Burns refers in his exquisite stanzas addressed to a mouse whose nest had been destroyed by his ploughshare, and beginning, “Wee, sleekit, cow’rin’, tim’rous beastie.” Such, indeed, is the fate of many a winter nest. Supposing, however, that the creature should be snapped up by the kestrel while out in search of food, the nest will be deserted, but it will not be wasted. There are always beings who are glad to find a ready-made burrow which will save them the trouble of excavating one for themselves. Among them are several species of wasp and humble-bee, most of whose nests are made in the deserted burrow of the campagnol.