destructive to birds than harriers. Another curious instance is that of the sociable hawk (Rostrhanrus sociabilis). This bird spends the summer and breeds in marshes in La Plata, and birds pay no attention to it, for it feeds exclusively on water-snails (Ampullaria). But when it visits woods and plantations to roost, during migration, its appearance creates as much alarm as that of a true buzzard, which it closely resembles. Wood-birds, unaccustomed to see it, do not know its peculiar preying habits, and how little they need fear its presence. I may also mention that the birds of La Plata seem to fear the kite-like Elanus less than other hawks, and I believe that its singular resemblance to the common gull of the district in its size, snowy-white plumage and manner of flight, has a deceptive effect on most species, and makes them so little suspicious of it. The wide-ranging peregrine falcon is a common species in La Plata, although, oddly enough, not included in any notice of the avifauna of that region before 1888. The consternation caused among birds by its appearance is vastly greater than that produced by any of the raptors I have mentioned: and it is unquestionably very much more destructive to birds, since it preys exclusively on them, and, as a rule, merely picks the flesh from the head and neck, and leaves the untouched body to its jackal, the carrion-hawk. When the peregrine appears speeding through the air in a straight line at a great height, the feathered world, as far as one able to see, is thrown into the greatest commo-tion, all birds, from the smallest up to species large as duck, ibis, and curlew, rushing about in the air as if distracted. When the falcon has disappeared in the sky, and the wave of terror attending its progress subsides behind it, the birds still continue wild and excited for some time, showing how deeply they have been moved; for, as a rule, fear is exceedingly transitory in its effects on animals.