"Below the wings spring long curved feathers, directed upwards; these are black on the inside, and brilliant green on the outside. The bill and feet are black."[206]
The same author, in referring to the brilliant metallic hues of this and other birds, takes occasion to notice the iridescent effect which is produced by the different angle at which light falls on the feathers. The emerald-green, for instance, will often fling out rays of its two constituent primary colours, at one time being blue-green, at another gold-green, while in certain lights all colour vanishes, and a velvet-black is presented to the eye. The ruby feathers of several birds become orange under certain lights, and darken to a crimson-black at other times.
This change of hue is analogous to the well-known iridescent changeableness of the nacre which lines various shells, and is owing to the structure of its surface reflecting the light in different rays, according to the angle at which it falls upon the feathers.
Another species, a native of the same teeming region, the Twelve-thread Epimachus, glows, with equal lustre, in the richest violet and emerald, but somewhat diversely arranged. The long, elegant depending tail is here reduced to ordinary dimensions, but, as if to compensate for this inferiority, the Twelve-thread is adorned with an expanding dress of the purest snowy white, composed of long silky plumes that spring from behind and below the wings, so soft and so loosely webbed as to wave gracefully in the slightest breeze. From these tufts project long and very slender shafts, unwebbed, and as fine as threads, curling elegantly, six on each side.
The little Sun-birds of India and Africa, and the still tinier Humming-birds of the New World are conspicuous for the metallic radiance of their plumage. Take for an example of the former the Fire-tailed Sun-bird of Nepâl. The crown and forehead are brilliant steel-blue, while the neck, the back, and the rump are of the richest scarlet, diversified by a broad patch of bright yellow across the middle of the back. The central feathers of the tail are lengthened, and are bright scarlet, while the lateral feathers are edged with the same rich hue on brown. The breast is golden yellow or orange, flushed with crimson in the centre, and the rest of the inferior parts are olive-green. Most of those gorgeous colours have a silky or metallic lustre, and blaze out under the tropical sunlight with amazing brightness.
Exquisite ornaments are these to an Indian garden, where they delight in the flowering plants and shrubs. They creep to and fro about the stalks and twigs, clinging by their little purple feet, and rifling the tubular corollas of the honeyed blossoms, whence doubtless they gather many minute insects, licked up with the nectar, by the aid of their curiously pencilled tongue.
For that peculiar charm which resides in flashing light combined with the most brilliant colours, the lustre of precious stones, there are no birds, no creatures, that can compare with the Humming-birds. Confined exclusively to America,—whence we have already gathered between three and four hundred distinct species, and more are being continually discovered,—these lovely little winged gems were to the Mexican and Peruvian Indians the very quintessence of beauty. By these simple people they were called by various names signifying "the rays of the sun," "the tresses of the day-star," and the like. Their glittering scale-like plumage was employed to make, at the cost of immense time, patience, and labour, the radiant mantles in which the emperors and highest nobles appeared on state occasions, as well as to form by a sort of mosaic, those embroidered pictures which so attracted the admiration of the Spanish conquerors. The Mexican priests adopted the tiny birds into their mythology: they taught that the souls of those warriors who died in defence of the gods, were conducted by Toyamiqui, the wife of the god of war, straight to the mansion of the sun, and there transformed into humming-birds.