As soon as spring comes back to the temperate zone, myriads and myriads of birds which are scattered over the warmer regions of the South come together in numberless bands, and, full of vigour and joy, hasten northwards to rear their offspring. Each of our hedges, each grove, each ocean cliff, and each of the lakes and ponds with which Northern America, Northern Europe, and Northern Asia are dotted tell us at that time of the year the tale of what mutual aid means for the birds; what force, energy, and protection it confers to every living being, however feeble and defenceless it otherwise might be. Take, for instance, one of the numberless lakes of the Russian and Siberian Steppes. Its shores are peopled with myriads of aquatic birds, belonging to at least a score of different species, all living in perfect peace--all protecting one another. "For several hundred yards from the shore the air is filled with gulls and terns, as with snow-flakes on a winter day. Thousands of plovers and sand-coursers run over the beach, searching their food, whistling, and simply enjoying life. Further on, on almost each wave, a duck is rocking, while higher up you notice the flocks of the Casarki ducks. Exuberant life swarms everywhere."(1) And here are the robbers--the strongest, the most cunning ones, those "ideally organized for robbery." And you hear their hungry, angry, dismal cries as for hours in succession they watch the opportunity of snatching from this mass of living beings one single unprotected individual. But as soon as they approach, their presence is signalled by dozens of voluntary sentries, and hundreds of gulls and terns set to chase the robber. Maddened by hunger, the robber soon abandons his usual precautions: he suddenly dashes into the living mass; but, attacked from all sides, he again is compelled to retreat. From sheer despair he falls upon the wild ducks; but the intelligent, social birds rapidly gather in a flock and fly away if the robber is an erne; they plunge into the lake if it is a falcon; or they raise a cloud of water-dust and bewilder the assailant if it is a kite.(2) And while life continues to swarm on the lake, the robber flies away with cries of anger, and looks out for carrion, or for a young bird or a field-mouse not yet used to obey in time the warnings of its comrades. In the face of an exuberant life, the ideally-armed robber must be satisfied with the off-fall of that life. Further north, in the Arctic archipelagoes, "you may sail along the coast for many miles and see all the ledges, all the cliffs and corners of the mountain-sides, up to a height of from two to five hundred feet, literally covered with sea-birds, whose white breasts show against the dark rocks as if the rocks were closely sprinkled with chalk specks. The air, near and far, is, so to say, full with fowls."(3)