Some flakes of snow have remained on this bough of spruce, pure white on dull green. Sparingly dispersed, the snow can be seen falling far ahead between the trunks; indeed, the white dots appear to increase the distance the eye can penetrate; it sees farther because there is something to catch the glance. Nothing seems left for food in the woods for bird or animal. Some ivy berries and black privet berries remain, a few haws may be found; for the rest, it is gone; the squirrels have had the nuts, the acorns were taken by the jays, rooks, and pheasants. Bushels of acorns, too, were collected by hand as food for the fallow deer in the park. A great fieldfare rises, like a lesser pigeon; fieldfares often haunt the verge of woods, while the redwing thrushes go out into the meadows. It can scarcely be doubted that both these birds come over to escape the keener cold of the winters in Norway, or that the same cause drives the blackbirds hither. In spring we listen to Norwegian songs--the blackbird and the thrush that please us so much, if not themselves of Scandinavian birth, have had a Scandinavian origin. Any one walking about woods like these in January can understand how, where there are large flocks of birds, they must find the pressure of numbers through the insufficiency of food. They go then to seek a warmer climate and more to eat; more particularly probably for sustenance. The original and simple theory that the majority of birds migrate for food or warmth is not overthrown by modern observations. That appears to be the primary impulse, though others may be traced or reasonably imagined. To suppose, as has been put forward, that birds are endowed with a migratory instinct for the express purpose of keeping down their numbers, in order, that is, that they may perish in crossing the sea, is really too absurd for serious consideration. If that were the end in view, it would be most easily obtained by keeping them at home, where snow would speedily starve them. On the contrary, it will appear to any one who walks about woods and fields that migration is essential to the preservation of these creatures. By migration, in fact, the species is kept in existence, and room is found for life. Apart from the necessity of food, movement and change is one of the most powerful agencies in renewing health. This we see in our own experience; the condition of the air is especially important, and it is well within reasonable supposition that some birds and animals may wish to avoid certain states of atmosphere. There is, too, the question of moulting and change of plumage, and the possibility that this physiological event may influence the removal to a different climate. Birds migrate principally for food and warmth; secondly, on account of the pressure of numbers (for in good seasons they increase very fast); thirdly, for the sake of health; fourthly, for sexual reasons; fifthly, from the operation of a kind of prehistoric memory; sixthly, from choice.