The frigate-birds of tropical seas, and the gannet of our own, display this mode of flight to perfection. It is worth going far to see a gannet dive. Travelling at a relatively considerable height, and eagerly scanning the surface of the water for signs of a shoal of fish, this amazing bird dives with the speed of lightning, and with half-spread wings disappears with a terrific plunge beneath the surface, to emerge, an instant later, with his prey. One can measure the force of such a plunge by the cruel trick, sometimes played by fishermen, of fastening a herring to a board, and setting it adrift where gannets are about. The unsuspecting victim descends as usual upon his prey, only to meet instant death by the shock of his impact with the board. Those who talk glibly of identifying birds by their flight may point to this wonderful diver as a case in point. But while one may often see the gannet on the wing, it is by no means so often that one will have the good fortune to see him dive, for he is not always hungry. His white body, pointed tail, and black quill-feathers would then enable the novice to name him at once. But--in his immature plumage, he would, at a little distance, appear black, and unless he were fishing, the chances of recognition would be by no means great. Close at hand he would appear speckled with white. [Illustration: _Brown Owl_] But this by the way. There are two other birds which dive from a height on the wing. One of these is the kingfisher: the other is the tern. The term "tern" is here used collectively, for there are several species, but all have this habit of diving from a height. During the summer months one may be quite sure of an opportunity of watching the graceful, easy flight of at least three species. For they haunt the sea-shore, river, and lake with equal impartiality. Those who are on the look-out for terns, for the first time, will easily recognise them. For, in the first place they look like miniature gulls, but with longer and more pointed wings, and forked tails. Further, all have a characteristic black cap. They travel in small parties, as if for company, keeping no more than a yard or two from the surface of the water, and scanning it eagerly in search of shoals of small fish, or crustacea. As these are found one will note a quickening of the wing-beat, and a sudden dive, like that of the gannet, with half-closed wings. And sometimes, too, the impetus will take them completely under water. [Illustration: 1 Bat 2 Butterfly 3 Beetle 4 Dragon-Fly 5 Bone of Birds Wing, Showing the three Divisions, Arm--Fore-arm--Hand. 6 Breast Bone of Swan 7 " " " Pigeon 8 " " " Pelican 9 & 10 Apteryx, Cassowary (degenerate wings). ] CHAPTER IV. Modes of Flight. "The soaring lark is blest as proud When at Heaven's gate she sings: The roving bee proclaims aloud Her flight by vocal wings."--_Wordsworth._