Those who have the good fortune to be able to make frequent visits to the Zoological Gardens in London may, with great good fortune, and at rare intervals, have an opportunity of witnessing such a display, and of studying in detail these wonderful wings. They are wonderful, not merely because of the manner of their display, or of their colouring, but also because in them we see ornament pushed to its furthest limit since, as wings, they have become well nigh useless, and therefore almost dangerous to the well-being of their possessors. [Illustration: Sunbittern Displaying.] CHAPTER VI. How to tell Birds on the Wing. "I can tell a hawk from a hernshaw."--_Shakespeare._ The small perching-birds and the difficulty of distinguishing them--The wagtails--The finches--The buntings--The redstart-wheatear, Stonechat--The thrushes--The warblers--The tit-mice--The nuthatch, and tree-creeper--The spotted-flycatcher--The red-backed shrike--swallows, martins, and swifts--The night-jar--owls--Woodpeckers. The experienced ornithologist apart, there are hosts of people who are interested, at least, in our native birds: who would fain call them all by name; yet who can distinguish no more than a very few of our commonest species. They are constantly hoping to find some book which will give, in a word, the "Hall-mark" of every bird they may meet in a day's march. But that book will never be written. For some species present no outstanding features by which they may be certainly identified, when no more than a momentary examination is possible, and this at a distance. And it is often extremely difficult to set down in words, exactly, what are the reasons for deciding that some rapidly retreating form belongs to this, or that, species. And then, too, there are difficulties due to seasonal changes of plumage--often striking--sex, and age; since immature birds often differ totally from the adults in appearance. The young robin and the starling afford instances in point. The adult starling, as everybody knows, is "black" with a yellow beak and reddish legs. But seen close at hand his feathers gleam with a wonderful metallic sheen reflecting changing hues of violet, green, and purple. The young bird, in the early summer, is of a pale brown colour. In the autumn the plumage is changed for a "black dress," like that of the adult, but heavily spotted with white. As the winter wears on the white spots become abraded, and disappear. The robin needs no description. But the young bird, in its first plumage, is commonly mistaken for the female, which, of course, is practically indistinguishable from the male. It is certainly unlike one's notion of a "cock-robin," being of a yellowish brown colour, with pale spots, a type of plumage characteristic of the young of the "thrush tribe." In some nearly related species, again, the males are strikingly different, the females barely distinguishable.