Rhea (bird) to be growing. The genus name was given in 1752 by Paul Möhring and adopted as the English common name. Möhring named the rhea based on the Greek Titan Rhea, whose name is derived from the Greek "Rhea" () from έρα "ground". This was fitting with the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally as "ñandú guazu" (Guaraní, meaning big spider, most probably in relation to their habit of opening and lowering alternate wings when they run), "ema" (Portuguese), "suri" (Aymara and Quechua), or "choique" (Mapudungun). "Nandu" is the common
Bird various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil. Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds. Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators. Although flightless, penguins use similar musculature