Page:The American Cyclopædia (1879) Volume VII.djvu/114

 106 FEATHERS the families of birds, and modify essentially their powers of flight. The breadth of the wing depends principally on the length of the secondary quills, and its length on that of the primaries. Leaving out of view the proportions of the bones and the force of the muscles of the wings, when the primaries are longest at the extremity of the pinion, as in the falcons and swallows, causing an acuminate form of wing, we may know that the powers of flight are great, requiring comparatively little exertion in the bird ; but when the longest primaries are in the middle of the series, giving rise to a short, broad wing, as in the partridge and grouse, the bird can fly only a short distance at a time, with great effort, and a whir well known to the sportsman. Not only the shape of the wing, but the close texture of its feathers, must be taken into account in the rapid strong flight of the falcon; the loose soft feathers of the wings in the owls, and the serrated outer edge of the primaries, while they prevent rapid flight, en- able them to pounce noiselessly upon their vigi- lant prey. Most birds, and especially the aqua- tic families, are provided with an oil gland at the base of the tail, whose unctuous secretion is distributed over the feathers by means of the bill, protecting their surface against moisture ; the shedding of the water is not owing entirely to the oily covering, but also to a thin plate of air entangled by the feathers, and probably also to an actual repulsion of the particles of water by the feathers, as is seen in the leaves of many aquatic plants ; the arranging of the plumes by the bill of the bird being rather to enable them to take down a large quantity of air, than to apply any repellent oily covering. The plumage of birds has an infinite variety of colors, from the sombre tints of the raven to the pure white of the egrets, and the gorgeous hues of the lory, toucan, trogon, and humming birds; the females have generally less lively colors, and the sum- mer livery of both sexes is often different from that of winter. One of the most curious phe- nomena connected with feathers is the annual moult, and the change of color during that and the breeding season; moulting usually takes place after the young have been hatched, the whole plumage becoming dull and rough, and the bird more or less indisposed, with a tem- porary loss of voice in the singing species. Ac- cording to Mr. Yarrell, the plumage of birds is changed by the mere alteration of the color of the feathers ; by the growth of new feathers without the loss of any old ones ; by the pro- duction of new feathers in the place of old ones thrown off, wholly or in part ; and by the wear- ing off of the light tips as the breeding season approaches, exposing the brighter tints under- neath. The first two of these changes occur in adults at the end of spring, the third being par- tial in spring and complete in autumn. Though the perfect plumage is non- vascular and epi- dermic, the colors change, probably by some vital process, without the loss of a feather; when the winter livery succeeding the autum- nal moult begins to assume its bright characters, the new color generally commences at the part of the web nearest the body, and gradually ex- tends to the tip. Until within the last few years the changes of color in the fur of mam- mals (as in the ermine in winter), and in the plumage of birds in the season of reproduction, were supposed to be effected by the simple reproduction of the hairs and feathers ; but this cannot be the case, as many facts go to prove that these changes occur at other times than the period of moulting, and without the loss of a hair or feather. It is well known that vivid emotions of fear or grief may turn the human hair gray or white in so short a period that there could be no change in the hair itself to account for it ; and a case is on record of a starling which became white after being rescued from a cat. It has been maintained by Schlegel and Martin that many birds always get their wedding plumage without moulting. The fact being admitted, how can the change of color be explained in the mature feather, which has no vascular or nervous communication with the skin ? The wearing away of the light tips, mentioned by Mr. Yarrell, is not only unphysi- ological, but in most cases does not happen. Dr. Weinland, from the examination of bleached specimens in museums, and of recent birds, ex- presses the belief that the brightness and fading of the colors are owing to the increase or dim- inution of an oily matter in the feathers; the. microscopic examination of the web of feathers from the breast of a fresh merganser (mergus serrator, Linn.) showed numerous lacuna of a reddish oil-like fluid; some weeks after, the same feathers, having become nearly white from exposure to light, disclosed air bubbles instead of the reddish fluid ; from this he con- cludes that the evaporation of the oily fluid, and the filling of the spaces with air as in the case of the white water lily, produces the changes of color. If this fluid be oily, as there is good reason to believe, mere physical imbi- bition would be sufficient to introduce it into the dead feathers, as it is well known that fat passes through all tissues very readily, even through compact horn. In the season of re- production, the nutritive and organic functions are performed with their utmost vigor, and the supply of fatty coloring matter would flow free- ly to the feathers ; under the opposite condi- tions of debility, cold, or insufficient food, the oily matter would be withdrawn and the feath- ers would fade. In regard to the value of feathers to man, it will be sufficient to enume- rate the ornamental employment of the plumes of the ostrich, egrets, cranes, and peacock; the economical uses of the down of the eider duck and the plumage of the goose ; the importance of the goose quill before the introduction of steel and gold pens, and the adherence of many at the present day to the more perishable, less convenient, but softer-moving quill; not to more than allude to the consumption of the plumage of the gorgeous tropical birds in the