_Rhea americana_, the so-called American Ostrich, the Ema of the Brazilians, the Avestruz, Nandú, or Chueké of Argentina, is found from Bolivia, Paraguay, and South Brazil to the Rio Negro, if not further; it is brownish-grey with blackish crown, nape, and breast, white thighs and abdomen, and yellowish neck. The sub-species _R. macrorhyncha_ of North-East Brazil is darker, with longer bill and more slender metatarsi. _R. darwini_, which occurs south of the Rio Negro, and up the Andes to Tarapaca, is buffish-brown, with whiter underparts and white margins to the {31}feathers of the wings and back. Hens are not so dark, and Mr. Hudson says[18] that in _R. darwini_ the young are dusky grey and are hatched with the legs feathered to the toes. Rheas are shorter than Ostriches by about a couple of feet, _R. americana_ being the largest form; the feathers are much rounded, broad, and very soft. Fossil remains occur in the Upper Tertiary or quite recent deposits of South America. [Illustration: FIG. 9.–Nandu. _Rhea americana._ × 1/20.] The members of this family find their favourite haunts on the treeless flats of the Argentine pampas, the scrub-covered plains of Patagonia, or the dry open Sertões of Brazil, where their acute vision enables them to detect the approach of enemies from afar. Small flocks of from three to seven individuals are met with at certain seasons, and parties of twenty or thirty at other times–often with deer or guanacos–so it would appear that, as in the case of the Ostrich, larger companies are formed after the young are able to provide for themselves. The birds become exceedingly tame when not molested, but when danger threatens they run at great speed, doubling upon their pursuers constantly, or crouching down among bushes or other cover, if they think they can escape observation. In the latter case they will lie closely until almost trodden upon, and may be shot before they rise by the hunter who cautiously approaches their hiding-place, as the head is usually visible above the surrounding vegetation. When moving at full pace the wings have normally a somewhat drooping position, but they are raised alternately above the back–apparently {32}to aid progress–when fresh exertions are necessary. Mr. Hudson tells us[19] that Darwin's Rhea "carries its neck stretched forward, which makes it seem lower in stature than the allied species." The diet consists chiefly of grass, roots, and seeds, but berries of _Empetrum_ are a favourite food, and lizards, insects, worms, and molluscs are said to be eaten, together with hard substances to promote digestion. Nandus take readily to the water, and can swim across a river several hundred yards wide, the body being hardly visible. In spring the cock utters a deep, resonant, booming noise, a loud hiss being not uncommonly heard also; while at that season the rival males attack each other viciously with their beaks, trampling down the ground in