Some species always live and move within such narrow limits, or, in other words, are so dependent on certain conditions, that we invariably think of them in association with their surroundings:--the snipe with the boggy soil; the rock-pipit with the rock-bound seashore; the tree-creeper with the tree he climbs upon; the lark with the cultivated fields; and the swift with the void blue sky, through which he is perpetually rushing. In like manner we invariably think of the dipper in connection with the swift, brawling mountain-torrent he inhabits. He is never, or very seldom, found removed from it, and is probably more restricted to certain conditions, and consequently more bound to his home, than any one of the species just named. The stream he attaches himself to must have quiet and comparatively deep pools, and the water must be clear to enable him to detect the larvæ of water-beetles, dragon-flies, and other aquatic insects he preys on, all of which have a protective colouring. He does not range up and down a stream, like the kingfisher, to visit the various feeding-places; he limits himself to a portion of it, in many cases not more than a hundred yards in length, and explores the bottoms of the same pools from day to day, until they must be as familiar to him--all their inequalities, their stony ridges and half-buried boulders, and sandy or pebbled places, and all the holes and secret corners where sediment collects--as the rooms we live in are to us, and about which we are able to move freely in the dimmest light. In ascending a mountain stream such as these birds love, abounding in deep, quiet pools, with noisy cascades and shallow rapids, its bottom strewn with great fallen boulders partly submerged, the rocky banks overgrown with sheltering bushes and vines, when you disturb a dipper he flies up stream a short distance, perhaps twenty yards, and alights on a boulder, or in the shadow of an overhanging rock, and there waits, silent and motionless, until, disturbed again, he takes a second short flight up stream, and so on to the limit of his range, whereupon, rising up and doubling back, he flies to the spot he started from. And as often as you disturb him he will act in the same way, going just so far, and no farther. If you leave him behind and go on, you will find another pair of dippers, whose portion of the stream begins just where that of the first pair ends. They, too, will act in the same way, and fly on until the end of their range is reached, and will not venture beyond where a third pair are in possession. Where they are not disturbed a mountain stream may be found parcelled out in this way among a dozen or twenty couples. Probably the dipper, like the robin, jealously resents the intrusion of another bird of his kind into his chosen ground. Concerning this habit of the dipper, and its strange way of feeding under the water, something still remains to be known.