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
Flightless bird that require a significant amount of overall metabolic energy, ratites decrease their basal metabolic rate and conserve energy. A study looking at the basal rates of birds found a significant correlation between low basal rate and pectoral muscle mass in kiwis. On the contrary, flightless penguins exude an intermediate basal rate. This is likely because penguins have well-developed pectoral muscles for hunting and diving in the water. For ground feeding birds, a cursorial lifestyle is more economical and allows for easier access to dietary requirements. Flying birds have different wing and feather structures that make flying easier, while flightless birds'