I must, before concluding this part of my subject, mention another raptor, also a true falcon, but differing from the peregrine in being exclusively a marsh-hawk. In size it is nearly a third less than the male peregrine, which it resembles in its sharp wings and manner of flight, but its flight is much more rapid. The whole plumage, is uniformly of a dark grey colour. Unfortunately, though I have observed it not fewer than a hundred times, I have never been able to procure a specimen, nor do I find that it is like any American falcon already described; so that for the present it must remain nameless. Judging solely from the effect produced by the appearance of this hawk, it must be even more daring and destructive than its larger relation, the peregrine. It flies at a great height, and sometimes descends vertically and with extraordinary velocity, the wings producing a sound like a deep-toned horn. The sound is doubtless produced at will, and is certainly less advantageous to the hawk than to the birds it pursues. No doubt it can afford to despise the wing-power of its quarry; and I have sometimes thought that it takes a tyrannous delight in witnessing the consternation caused by its hollow trumpeting sound. This may be only a fancy, but some hawks do certainly take pleasure in pursuing and striking birds when not seeking prey. The peregrine has been observed, Baird says, capturing birds, only to kill and drop them. Many of the Felidae, we know, evince a similar habit; only these prolong their pleasure by practising a more refined and deliberate cruelty. The sudden appearance overhead of this hawk produces an effect wonderful to witness. I have frequently seen all the inhabitants of a marsh struck with panic, acting as if demented, and suddenly grown careless to all other dangers; and on such occasions I have looked up confident of seeing the sharp-winged death, suspended above them in the sky. All birds that happen to be on the wing drop down as if shot into the reeds or water; ducks away from the margin stretch out their necks horizontally and drag their bodies, as if wounded, into closer cover; not one bird is found bold enough to rise up and wheel about the marauder--a usual proceeding in the case of other hawks; while, at every sudden stoop the falcon makes, threatening to dash down on his prey, a low cry of terror rises from the birds beneath; a sound expressive of an emotion so contagious that it quickly runs like a murmur all over the marsh, as if a gust of wind had swept moaning through, the rushes. As long as the falcon hangs overhead, always at a height of about forty yards, threatening at intervals to dash down, this murmuring sound, made up of many hundreds of individual cries, is heard swelling and dying away, and occasionally, when he drops lower than usual, rising to a sharp scream of terror.