+Haliaëtus melanoleucus+, _Burm. La-Plata Reise_, ii. p. 435 (Paraná, Tucuman, Pampas). +Geranoaëtus melanoleucus+, _Scl. et Salv. Nomencl._ p. 119; _Hudson, P. Z. S._ 1872, p. 536 (Rio Negro); _Durnford, Ibis_, 1877, p. 38, et 1878, p. 397 (Patagonia); _Gibson, Ibis_, 1879, p. 409 (Buenos Ayres); _Barrows, Auk_, 1884, p. 110 (Entrerios and Ventana). +Buteo melanoleucus+, _Sharpe, Cat. B._ i. p. 168. _Description._--Above black, wings grey, with narrow transverse black bars; tail black: beneath, throat grey; breast black, with slight round whitish spots; abdomen white, faintly barred across with grey; bill plumbeous; feet yellow, claws black: whole length 26·0 inches, wing 19·0, tail 10·5. _Female_ similar, but larger. _Hab._ Whole southern half of South America, and western portion of northern half. The Grey or Chilian Eagle, like most diurnal birds of prey, undergoes many changes of colour, the plumage at different periods having its brown, black, and grey stages: in the old birds it is a uniform clear grey, and the under surface white. Throughout the Argentine country this is the commonest Eagle, and I found it very abundant in Patagonia. D'Orbigny describes it with his usual prolixity--pardonably so in this case, however, the bird being one of the very few species with which he appears to have become familiar from personal observation. He says that it is a wary bird; pairs for life, the male and female never being found far apart; and that it soars in circles with a flight resembling that of a Vulture, and that the form of its broad blunt wings increases its resemblance to that bird. Cavies and small mammals are its usual prey; and in the autumn and winter, when the Pigeons congregate in large numbers, it follows their movements. During the Pigeon-season, he has counted as many as thirty Eagles in the course of a three leagues' ride; and he has frequently seen an Eagle swoop down into a cloud of Pigeons, and invariably reappear with one struggling in its talons. It is seldom found far from the shores of the sea or of some large river; and on the Atlantic coast, in Patagonia, it soars above the sands at ebb-tide, looking out for stranded fish, carcases of seals, and other animal food left by the retiring waters, and quarrels with Condors and Vultures over the refuse, even when it is quite putrid. It acts as a weather prognostic, and before a storm is seen to rise in circles to a vast height in the air, uttering piercing screams, which may be heard after it has quite disappeared from sight. The nest of this species is usually built on the ledge of an inaccessible rock or precipice, but not unfrequently on a tree. Mr. Gibson describes one, which he found on the top of a thorn-tree, as a structure of large sticks three feet in diameter, the hollow cushioned with dry grass. It contained two eggs, dull white, marked with pale reddish blotches.