Another result of their immunity from persecution is the splendid colouring and strange and beautiful feather ornaments distinguishing them above all other birds; and excessive variation in this direction is due, it seems to me, to the very causes which serve to check variation in all other directions. In their plumage, as Martin long ago wrote, nature has strained at every variety of effect and revelled in an infinitude of modifications. How wonderful their garb is, with colours so varied, so intense, yet seemingly so evanescent!--the glittering mantle of powdered gold; the emerald green that changes to velvet black; ruby reds and luminous scarlets; dull bronze that brightens and burns like polished brass, and pale neutral tints that kindle to rose and lilac-coloured flame. And to the glory of prismatic colouring are added feather decorations, such as the racket-plumes and downy muffs of Spathura, the crest and frills of Lophornis, the sapphire gorget burning on the snow-white breast of Oreotrochilus, the fiery tail of Cometes, and, amongst grotesque forms, the long pointed crest-feathers, representing horns, and flowing-white beard adorning the piebald goat-like face of Oxypogon. Excessive variation in this direction is checked in nearly all other birds by the need of a protective colouring, few kinds so greatly excelling in strength and activity as to be able to maintain their existence without it. Bright feathers constitute a double danger, for not only do they render their possessor conspicuous, but, just as the butterfly chooses the gayest flower, so do hawks deliberately single out from many obscure birds the one with brilliant plumage; but the rapacious kinds do not waste their energies in the vain pursuit of hummingbirds. These are in the position of neutrals, free to range at will amidst the combatants, insulting all alike, and flaunting their splendid colours with impunity. They are nature's favourites, endowed with faculties bordering on the miraculous, and all other kinds, gentle or fierce, ask only to be left alone by them. CHAPTER XVII. THE CRESTED SCREAMER. _(Chalina chavarria.)_