Rheas (Aves, Rheiformes) are large flightless birds native to South America. The name was given in 1752 by P. H. G. Mohring (what prompted his bestowal of this name, so well known in classical mythology, is not apparent). Though long before known and described by the earlier writers—Nieremberg, Marcgrav and Piso (the last of whom has a recognizable but rude figure of it), the species had been without any distinctive scientific appellation. Adopted a few years later by M. J. Brisson, the name has since passed into general use, especially among English authors, for what their predecessors had called the American ostrich; but on the European continent the bird was commonly called Nandu, a word corrupted from a name it is said to have borne among the aboriginal inhabitants of Brazil, where the Portuguese settlers called it ema (see emu). The name Touyou, also of South American origin, was applied to it by Brisson and others, but erroneously, as Cuvier shows, since by that name, or something like it, the jabiru is properly meant.
The resemblance of the rhea to the ostrich was at once perceived, but the differences between them are also very evident. The former, for instance, has three instead of two toes on each foot, it has no apparent tail, its wings are far better developed, and when folded cover the body, and its head and neck are clothed with feathers, while internal distinctions of still deeper significance have since been dwelt upon by T. H, Huxley (Proc. Zool. Society, 1867, pp. 420— 422) and W. A. Forbes (op. cit., 1881, pp. 784—87). There can be little doubt that they should be regarded as types of as many orders—Struthiones and Rheae—of the subclass Ratitae. Structural characters no less important separate the rheas from the emus; the former can be readily recognized by the rounded form of their contour-feathers, which want the hyporrhachis or -after-shaft that in the emeus and cassowaries is so long as to equal the main shaft, and contributes to give these latter groups the appearance of being covered with shaggy hair. It is polygamous, and the male performs the duty of incubation, brooding more than a score of eggs, the produce of several females—facts known to Nieremberg more than three hundred and fifty years since but not accepted by naturalists until about a century ago. No examples of this bird seem to have been brought to Europe before the beginning of the 20th century, and accordingly the descriptions previously given of it by systematic writers were taken at second hand and were mostly defective if not misleading. In 1803 J. Latham issued a wretched figure of the species from a half-grown specimen in the Leverian Museum, and twenty years later said he had seen only one other, and that still younger, in Bullock's collection (Gen. Hist. Birds, viii. p. 379; the ninth edition of the Companion to this collection (1810, p. 121) states that the specimen "was brought alive" to England]). A bird living in confinement at Strassburg in 1806 was, however, described and figured by Hammer in 1808 (Ann. du Museum, xii. pp. 427—433, p1. 39). In England the Report of the Zoological Society for 1833 announced the rhea as having been exhibited for the first time in its gardens during the preceding twelvemonth. Since then many other living examples have been introduced, and it has bred both there and in many private parks in Britain.
Though considerably smaller than the ostrich, and wanting its fine plumes, the rhea in general aspect far more resembles that bird than the other Ratitae. The feathers of the head and neck, except on the crown and nape, where they are ‘dark brown. are dingy white, and those of the body ash-coloured tinged with brown, while on the breast they are brownish-black, and on the belly and thighs white. In the course of the memorable voyage of the "Beagle," Charles Darwin came to hear of another kind of rhea, called by his informants Aveslruz petise, and at Port Desire on the east coast of Patagonia he obtained an example of it, the imperfect skin of which enabled J. Gould to describe it (Proc. Zool. Society, 1837, p. 35) as a second species of the genus, naming it after its discoverer. Rhea darwini differs in several well-marked characters from the earlier known Rhea americana. Its bill is shorter than its head, its tarsi are reticulated instead of scutellated in front, with the upper part feathered instead of being bare; and the plumage of its body and wings is very different, each feather being tipped with a distinct whitish band, while that of the head and neck is greyish-brown. A further distinction is also asserted to be shown by the eggs—those of Rhea americana being of a yellowish-white, while those of Rhea darwini have a bluish tinge. Some years afterwards P. L. Sclater described (op. cit., 1860, p. 207) a third and smaller species, closely resembling the Rhea americana, but having apparently a longer bill, whence he named it Rhea macrorhyncha, more slender tarsi, and shorter toes, while its general colour is very much darker, the body and wings being of a brownish-grey mixed with black. The precise geographical range of these three species is still undetermined. While Rhea americana is known to extend from Paraguay and southern Brazil through the La Plata region to an uncertain distance in Patagonia, Rhea darwini seems to be the proper inhabitant of the country last named, though M. Claraz asserts (op. cit., 1885, p. 324) that it is occasionally found to the northward of the Rio Negro, which had formerly been regarded as its limit, and, moreover, that flocks of the two species commingled thay be very frequently seen in the district between that river and the Rio Colorado. On the "pampas" Rhea americana is said to associate with herds of deer (Cariacus campestris), and Rhea darwini to be the constant companion of guanacos (Lama huanaco)—just as in Africa the ostrich seeks the society of zebras and antelopes. As for Rhea macrorhyncha, it was found by W. A. Forbes (Ibis, 1881, pp. 360, 361) to inhabit the dry and open "sertoës" of north-eastern Brazil, a discovery the more interesting since it was in that part of the country that Marcgrav and Piso became acquainted with a bird of this kind, though the existence of any species of rhea in the district had been long overlooked by or unknown to succeeding travellers.
initial text taken from a 1911 encyclopedia