Biggest bird of South America. These birds have long necks compared to their body, strong and long legs. A decline in the population of Greater rheas is of great concern, and many organizations are taking conservative measures to protect this species. The hatching time is coordinated when the first egg ready to hatch makes a pop-bottle rocket sound. Male Greater rheas are responsible for building nests and taking care of the feed. They can measure 50-55 inches in long and are as tall as 4 ft 7 in - 5 ft 7 in. They run at a speed of 72 kmph. Near threatened.