I had been telling a child about the miracle of migration, and when I had finished, she routed all my science by the simplest of questions, and utterly posed me by asking: "_What do they do it for?_" Yes, indeed, what _do_ they do it for? or what do they do it _for_? It does not matter which word we put the emphasis on: it is the same conundrum always from a slightly different angle; only another turn in the maze. As the child got no reply, she helped herself to one, and satisfactorily remarked: "_Perhaps they've got to._" She had gathered from my description that there could be nothing agreeable to the birds in the migration, and, logically enough, since one only does that which is disagreeable from necessity, she inferred compulsion. But she set me thinking, and since science attempts no explanation of this appalling Kismet of the birds, I tried to find a reason for it for myself. And there can only be this, that it is one of Nature's methods for reducing numbers. At any rate, wherever we turn our eyes in Nature, we find her bringing forth in vast excess of her requirements, and then restoring the equilibrium by the institution of active scourges, or terrific epidemics of suicide. There is no need for the birds to cross seas: to travel twice a year from the Hebrides to Abyssinia. Do they want a warmer climate? do they want a cooler? They have only to remain where they are and change their altitude. Do they need food? The idea is preposterous. They leave their various countries at seasons when their food is most abundant; they are then well fed, and are then strongest for the terrific ordeal before them. Besides, imagine a bird in, say Egypt, coming to England for food! No, that is the least reasonable of all explanations. And no other is much better. So we have to fall back on the child's reason, "Perhaps they do it because they've got to." Twice in every year do they start off, these little [Illustration: MOBBING THE GREAT SEA LANTERN] pilgrims, along the broad highways of massacre, walled in, as it were, with disaster on either side, running the gauntlet of ambush and open warfare all along the line. The myriads that perish before they reach us are beyond computation. But the survivors rear new broods, the gaps by death are all filled by birth, and off they go again once more, giving hostages to pitiless calamity, and strewing afresh in Autumn the tracks of Spring with countless corpses. But I did not tell the child this. She would have said the birds were "stupid," and thought, perhaps, the less of them and the worse.