This is one of the commonest birds in South America, and has a wide geographical range. It is found in Mexico and in the West Indies. It is also, according to M. Audubon, an occasional visitant to the Floridas; it takes its name from Brazil, but is no where so common as on the grassy savannahs of La Plata. It generally follows man, but is sometimes found even on the most desert plains of Patagonia: in the northern part of that region, numbers constantly attended the line of road between the Rio Negro and the Colorado, to devour the carcasses of the animals which chanced to perish from fatigue. Although abundant on the open plains of this eastern portion of the continent, and likewise on the rocky and barren shores of the Pacific, nevertheless it inhabits the borders of the damp and impervious forests of Tierra del Fuego and of the broken coast of West Patagonia, even as far south as Cape Horn. The Carranchas (as the Polyborus Brasiliensis is called in La Plata) together with the P. chimango[[6]], attend in great numbers the estancias and slaughtering houses in the neighbourhood of the Plata. If an animal dies in the plain, the Cathartes atratus or Gallinazo commences the feast, and then these two carrion-feeding hawks pick the bones clean. Although belonging to closely allied genera, and thus commonly feeding together, they are far from being friends. When the Carrancha is quietly seated on the branch of a tree, or on the ground, the Chimango often continues flying backwards and forwards for a long time, up and down in a semicircle, trying each time, at the bottom of the curve, to strike its larger relative. The Carrancha takes little notice, except by bobbing its head. Although the Carranchas frequently assemble in numbers, they are not gregarious; for in desert places they may be seen solitary, or more commonly by pairs. Besides the carrion of large animals, these birds frequent the borders of streams and the sea beach, for the sake of picking up whatever the waters may cast on shore. In Tierra del Fuego, and on the west coast of Patagonia, they must live almost exclusively on this last means of supply.
The Carranchas are said to be very crafty, and to steal great numbers of eggs; they attempt also, together with the Chimango, to pick the scabs off the sore backs of both horses and mules. On the one hand, the poor animal, with its ears down and its back arched; and, on the other, the hovering bird, eyeing at the distance of a yard, the disgusting morsel, form a picture which has been described by Captain Head with his own peculiar spirit and accuracy. The Carranchas kill wounded animals; but Mr. Bynoe (the surgeon of the Beagle) saw one seize in the air a live partridge, which, however, escaped, and was for some time chased on the ground. I believe this circumstance is very unusual: at all events there is no doubt that the chief part of their sustenance is derived from carrion. A person will discover their necrophagous habits by walking out on one of the desolate plains, and there lying down to sleep: when he awakes, he will see on each surrounding hillock, one of these birds patiently watching him with an evil eye. It is a feature in the landscape of these countries, which will be recognised by every one who has wandered over them. If a party goes out hunting with dogs and horses, it will be accompanied during the day, by several of these attendants. The uncovered craw of the Carrancha, after feeding, protrudes from its breast; at such times it is, and indeed generally, an inactive, tame, and cowardly bird. Its flight is generally heavy and slow, like that of the English carrion crow, whose place it so well supplies in America. It seldom soars; but I have twice seen one at a great height gliding through the air with much ease. It runs (in contradistinction to hopping), but not quite so quickly as some of its congeners. At times the Carrancha is noisy, but is not generally so; its cry is loud, very harsh and peculiar, and may be compared to the sound of the Spanish guttural g, followed by a rough double r r. Perhaps the Spaniards of Buenos Ayres, from this cause, have called it Carrancha. Molina, who says it is called Tharu in Chile, states, that when uttering this cry, it elevates its head higher and higher, till at last, with its beak wide open, the crown almost touches the lower part of the back. This fact, which has been doubted, is true; for I have myself several times seen them with their heads backwards, in a completely inverted position. The Carrancha builds a large coarse nest, either in a low cliff, or in a bush or lofty tree. To these observations I may add, on the high authority of Azara, whose statements have lately been so fully confirmed by M. D’Orbigny, that the Carrancha feeds on worms, shells, slugs, grasshoppers, and frogs; that it destroys young lambs by tearing the umbilical cord: and that it pursues the Gallinazos and gulls which attend the slaughtering-houses, till these birds are compelled to vomit up any carrion they may have lately gorged. Lastly, Azara states that several Carranchas, five or six together, will unite in chase of large birds, even such as herons. All these facts show that it is a bird of very versatile habits and considerable ingenuity.
I am led to suppose that the young birds of this species sometimes congregate together. On the plains of Santa Cruz (lat. 50° S. in Patagonia), I saw in the month of April, or early autumn, between twenty and thirty Polybori, which I at first thought would form a species distinct from P. Brasiliensis. Amongst those I killed, there were some of both sexes; but the ovarium in the hens was only slightly granular. The plumage of the different individuals was nearly similar; and in none appeared like that of an adult bird, although certainly not of a very young one. Having mentioned these circumstances to Mr. Gould, he likewise suspected it would form a new species; but the differences appear so trifling between it and the specimens of young birds in the British Museum and in the Museum of the Zoological Society, and likewise of the figure of a young bird given by Spix, (Avium Species Novæ, vol. i. p. 3.), that I have thought it advisable merely to allude to the circumstance. In my specimen, which is a cock, the head, instead of being of a dark brown, which is the usual character of even very immature birds, is of a pale rusty brown. The bill and cere are less produced than in the adult P. Brasiliensis; and the cere is of a brighter colour, than what appears to be usual in the young of this species. In other respects there is such a perfect similarity between them, that I do not hesitate to consider my specimen as a young bird of the P. Brasiliensis in one of its states of change;—and to be subject to great variation of plumage during growth, is known to be a character common to the birds of this sub-family. It may, however, possibly be some variety of the P. Brasiliensis, for this bird seems subject to variation: Azara (Voyage dans l’Amérique Méridionale, vol. iii. p. 35.) remarks, “Il y a des individus dont les teintes sont plus faibles, ou d’un brun pâle, avec des taches sur la poitrine, et d’autres qui ont des couleurs plus foncées; j’ai décrit ceux qui tiennent le milieu entre les uns et les autres.”
I have myself more than once observed a single very pale coloured bird, in form like the P. Brasiliensis, mingled with the other carrion-feeding hawks on the banks of the Plata; and there is now in the British Museum a specimen, which may be considered as partly an albino. Spix, on the other hand, (Avium Species Novæ, p. 3.) has described some specimens from the coast of Brazil, as being remarkable from the darkness of the plumage of their wings.
Milvago, Spix.
Several new genera have lately been established to receive certain species of the sub-family of Polyborinæ, and consequently great confusion exists in their arrangement. Mr. George R. Gray has been kind enough to give me the following observations, by which it appears he has clearly made out, that Spix’s genus Milvago, is that which ought to be retained. M. D’Orbigny has made two sections in the genus Polyborus, according as the craw is covered with feathers, or is naked, and he states that the P. Brasiliensis is the only species which comes within the latter division; but we shall afterwards see that the Falco Novæ Zelandiæ, Auct. (the Milvago leucurus of this work) has a naked craw, which is largely protruded after the bird has eaten. M. D’Orbigny has also instituted the genus Phalcobænus, to receive a bird of this sub-family, with the following characters:
“Bec fortement comprimé, sans aucune dent ni sinus, à commissure trèsarquée à son extrémité; cire alongée et droite; un large espace nu entourant la partie antérieure et inférieure de l’œil, et s’étendant sur toute la mandibule inférieure; tarses emplumés sur un tiers de leur longueur, le reste réticulé; doigts longs, semblables à ceux des gallinacés, terminés par les ongles longs, deprimés et élargis, très-peu arqués, toujours à extrémité obtuse ou fortement usée; ailes de la famille, la troisième penne plus longue que les autres.”
Mr. George R. Gray, however, has pointed out to me that Spix, (in his Avium Species Novæ) ten years since, made a division in this sub-family, from the rounded form of the nostril of one of the species, namely, the M. ochrocephalus of his work, or the Chimachima of Azara. And Mr. Gray thinks, that all the species may be grouped much more nearly in relation to their affinities by this character, than by any other: he further adds;—“The only difference which I can discover between this latter genus (Milvago), and D’Orbigny’s (Phalcobænus), is, that in the latter the bill is rather longer, and not quite so elevated in the culmen as in the former; and these characters must be considered too trivial for the foundation of a generic division. I, therefore, propose to retain Spix’s genus, Milvago, for all those Polyborinæ which possess rounded nostrils with an elevated bony tubercle in the centre. They were once considered to form three distinct genera, viz.—Milvago, Spix. (Polyborus, Vieill. Haliaëtus, Cuv. Aquila, Meyen.)—Senex, Gray. (Circaëtus, Less.)—Phalcobænus, D’Orb. but a careful comparison of the several species, shows a regular gradation in structure from one to the other, which induces me to consider them as only forming two sections of one genus. Those which have the bill short, with the culmen arched, and are of small size, slender form, and with the tarsi rather long and slender, are—
1. Milvago ochrocephalus, Spix. Polyborus chimachima; Vieill. (young). Falco degener, Licht. Haliaëtus chimachima, Less. 2. Milvago pezoporos, nob. Aquila pezopora, Meyen. 3. Milvago chimango, n. Polyborus chimango, Vieill. Haliaëtus chimango, Less.
Those which have a buteo-like appearance, and with rather short and stout tarsi, are,