Mr. Mudie, in his "Feathered Tribes," observes--"A question has been raised how the Dipper can contrive to keep beneath a fluid so much more dense than itself. An Owl to an Owl's bulk of air is as a stone to a pound, as compared with the Dipper's bulk of water to the Dipper; but if birds rise and ascend in the air at pleasure by the motions of their wings, it is only reversing those motions to enable them to descend or keep themselves down in water. The difference of specific gravity between the bird and the water is indeed so trifling that very little effort suffices to move it in any direction, upwards, downwards, or laterally. Birds do not fly upon the principle of specific gravity, as, with equal wings, the heavy birds fly best; they fly because they strike the air more forcibly in the opposite direction to that in which they wish to go, and, under water, the Dipper just does the same. If it wishes to go down, it strikes upwards with the wings and tail; if to come up, it does just the reverse. The only difference is that the wings are held 'recovered,' as running birds use them, and that gravitation has even less to do in the matter than in flying. Any one who has ever seen a Dipper under water, or has the slightest knowledge of the mere elements of mechanics, can understand the whole matter in an instant. The Dipper is indeed often adduced as an instance of the beautiful simplicity of animal mechanics." The flight of the Water Ouzel is effected by a series of rapidly repeated strokes, yet, even when winging its way through the air, the bird skims along near the surface of the stream, darting down from time to time to seize a passing insect. Only when hotly pursued does it quit the vicinity of its favourite lake or river, and seek safety by flying to any considerable distance, and it always returns to its usual haunts as soon as the cause of its alarm has disappeared. While perched upon an elevated point on the bank, engaged in watching for prey, it is not uncommon to see it dart suddenly down and seize its victim with an action more resembling the leap of a frog than the movement of a member of the feathered creation. As regards intelligence and the perfection of its senses, this remarkable bird is decidedly highly endowed; its sight and hearing, in particular, are extremely acute. In disposition it is cunning, cautious, and so observant that it at once perceives any unusual object or detects approaching danger.