The commonest method of exhibiting color is by means of pigments either in the external coating of the feathers or in their deeper layers. Cases of this sort are too frequent to need special exemplification; but some birds have brilliant hues otherwise displayed, as in the wattles of the common barn-door fowl, the fleshy appendages of the turkey, and the painted face of the carrier-pigeon. The wattled honey-sucker of Australia has two drooping folds of flesh which fall like bonnet-strings under his throat; the king-vulture has his head and neck covered with naked skin of every hue in the rainbow; and the cassowary (by far the most frugivorous of all the ostrich tribe) has the same parts of a brilliant red, variegated with melting shades of blue. In many other birds the beak becomes an ornamental adjunct; and this tendency reaches its furthest development in the bill of the toucan, whose colors almost vie with the humming-bird itself. But the most curious of all such aesthetic modifications is that from which the wax-wings derive their name. In these birds the shafts of certain wing-feathers are prolonged into small, horny expansions, bright scarlet in hue, exactly resembling, both in color and texture, little tags of red sealing-wax.
The metallic luster of feathers is generally due to fine lines on the surface of the barbules, like those which produce the iridescence of mother-of-pearl. Such luster occurs in the sun-birds and hummingbirds, and on many other less ornamented species. Sometimes gleaming like gold or bronze, sometimes fading away into jetty black, anon reappearing as glancing outbursts of crimson, azure, or exquisite green, it has gained for the birds on which it appears such poetical names as ruby-throated, topaz-crested, amethystine, golden, emerald, and sapphire. Not only does it occur upon the burnished neck of the dove, but it gives a passing splendor to the sable livery of the crow, and throws a thousand changeful hues over the glossy plumage of the mallard.
But besides the ornamental effects of color and luster, feathers appeal to the æsthetic taste of birds by their form, their arrangement, and their variety. Only the plainest birds have all their plumage exactly uniform and simply disposed. In an immense number of species certain feathers have been specially modified in shape so as to form crests, fan-like tails, lappets, and other ornaments. And just as a good architect lavishes his decorations chiefly on the constructive points of his building, the critical parts, such as arches, doorways, windows, and architraves, so do we find that birds have chosen to place their decorative modifications on the most important nodal points of their bodies, and that they generally lavish their richest coloring upon these ornamental adjuncts. This peacock's feather, for instance, formed part of a gorgeous semicircular fan, which composed, as it were, the background or reredos of the whole living picture when expanded, and the train of the majestic sultan when folded in repose. A plume from the neck or back, though still beautiful with golden green and
