All who watch the flight of hawks or kites are struck by the extraordinary power they have of sustaining themselves for a long time, sailing about in the air without flapping their wings or making any conspicuous effort whatever.

Most birds of prey, as distinguished from game, are able to do this, and thus hold commanding heights from which, to descry food. The expression “wind-sucker,” as used by Ben Jonson, refers to the kestrel, a kind of hawk unsuited for falconry ; the astonishing way in which it keeps itself poised in the air, facing the wind with beak outstretched, led to the name, which implies the only explanation of the phenomenon that the science of those days could furnish. Sea-birds are also very proficient.