154. Next; the physician (over whom, to get the letter out of him, I had to use the authority of a more than ordinarily imperious patient) says,—
"Now for the grebes lowering themselves in water, (which Lucy said I was to tell you about). The way in which they manage it, I believe to be this. Most birds have under their skins great air-passages which open into the lungs, and which, when the bird is moving quickly, and consequently devouring a great deal of air, do, to a certain extent, the work of supplementary lungs. They also lessen the bird's specific gravity, which must be of some help in flying. And in the gannet, which drops into the sea from a great height after fish, these air-bags lessen the shock on striking the water. Now the grebes (and all diving-birds) which can swim high up out of water when the air-cushions are full, and so feel very little the cold of the water beneath them, breathe out all spare air, and sink almost out of sight when they wish to be less conspicuous;—just as a balloon sinks when part of the gas is let out. And I have often watched the common divers and cormorants too, when frightened, swimming about with only head and neck out of water, and so looking more like snakes than birds.
"Then about the Dippers: they 'fly' to the bottom of a stream, using their wings, just as they would fly up into the air; and there is the same difficulty in flying to the bottom of the stream, and keeping there, as there would be in flying up into the air, and keeping there,—perhaps greater difficulty.
"They can never walk comfortably along the bottom of a river, as they could on the bank, though I know they are often talked of as doing it. They too, no doubt, empty their air-bags, to make going under water a little less difficult."
155. This most valuable letter, for once, leaves me a minute or two, disposed to ask a question which would need the skinning of a bird in a diagram to answer—about the "air-passages, which are a kind of supplementary lungs." Thinking better of it, and leaving the bird to breathe in its own way, I do wish we could get this Dipper question settled,—for here we are all at sea—or at least at brook, again, about it: and although in a book I ought to have examined before—Mr. Robert Gray's 'Birds of the West of Scotland,' which contains a quantity of useful and amusing things, and some plates remarkable for the delicate and spirited action of birds in groups,—although, I say, this unusually well-gathered and well-written book has a nice little lithograph of two dippers, and says they are quite universally distributed in Scotland, and called 'Water Crows,' and in Gaelic 'Gobha dubh nan allt,' (which I'm sure must mean something nice, if one knew what,) and though it has a lively account of the bird's ways out of the water—says not a word of its ways in it! except that "dippers everywhere delight in deep linns and brawling rapids, where their interesting motions never fail to attract the angler and bird-student;" and this of their voices: "In early spring, the male birds may be seen perched on some moss-covered stone, trilling their fine clear notes;" and again: "I have stood within a few yards of one at the close of a blustering winter's day, and enjoyed its charming music unobserved. The performer was sitting on a stake jutting from a mill-pond in the midst of a cold and cheerless Forfarshire moor, yet he joyously warbled his evening hymn with a fullness which made me forget the surrounding sterility."
Forget it not, thou, good reader; but rather remember it in your own hymns, and your own prayers, that still—in Bonnie Scotland, and Old England—the voices, almost lost, of Brook, and Breeze, and Bird, may, by Love's help, be yet to their lovers audible. Ainsi soit il.
Brantwood, 8th July, 1881.
Footnotes