Darwin's Rhea is often included with Puna Rhea P. tarapacensis in a single species known as Lesser Rhea. Darwin's Rhea is distributed in Patagonia while Puna Rhea is distributed in northern Chile. The two groups are separated by a large area of unsuitable habitat.

Like other ratites, the female may mate with several males and it is the male that looks after the chicks as was the case with the birds in these photos.