The emu makes hissing, grunting, booming sounds. As well, rheas can stand colder weather than ostriches. The thin, fine feathers of Rheas are grayish brown. One interesting fact is that the egg shells change colour after they are laid. When they are laid they are green and then through incubation they become yellow, followed by blue and then white by the time they hatch.
Rheas make a whistling noises and deep booming sounds.
Herbert S. Zim. William Morrow and Co., 1958.