Indeed, we have here one of the great secrets of bird success; for while most animals must roam within limited districts, and get their food there as best they can, thousands and tens of thousands of birds set off, when the colder weather makes food scarce in any one region, and travel hundreds of miles to more genial climates, where insects are still to be found, and the trees are still covered with fruit and leaves. How strange it is to think that while we are making the best of our winter, the swallow has taken her unerring flight to Africa, the swans and cranes have long since made their southward journey, and myriads of small birds have gone in search of food and warmth, to return next spring as certainly to their old haunts, where they can breed in cool and comfortable quarters! If we could only get the birds to tell us how they have learned the routes they take, and by what rules they are guided! One thing we know, that each kind of bird makes its nest in the coldest region which it visits, and where, at the time its young brood are ready, insect and other life is abundant; so that while the wild duck and goose, the woodcock, snipe, and field-fare, go to the far north to lay their eggs, and come to us in the sharper weather to feed when there is nothing but ice and snow in the home they have left, the swallow, the cuckoo, the swift, and the wheatear, on the other hand, visit us in the spring to build, and when autumn comes on take their flight to Africa and the East; and even many of the song-thrushes and robin-redbreasts which remain with us in England start off from Germany to warmer climates. Others, again, such as some of the Reed-warblers, the Stint, and the Ortolan Bunting, only make our island a house of call between the arctic regions where they breed in the summer when mosquitoes are swarming there, and the south where they winter after flying thousands of miles. It would take too long to discuss here why and how they go, even if we knew it with certainty; but it is most probable that their ancestors first learned the routes now taken when Europe and Africa had not so wide a sea between them, and we can see that it must be a great advantage to be able to travel from climate to climate, so as to find a plentiful table spread at all times of the year; while they may return to the north to breed, not merely because there is food there, but also because in still earlier times, when the northern countries were much warmer than they are now, they doubtless lived there altogether, and, though now obliged to go south, have never lost the tradition of their old home.