The greater rhea is the largest bird in South America. Related to the ostrich and emu, the greater rhea cannot fly. This polygamous bird does lay several eggs though. Females lay one egg every other day for seven to 10 days. Because males have several mates, and the females put their eggs in the same nest, which sometimes holds up to 50 eggs. The male is in charge of incubating the eggs of all its mates for six weeks, until the young are hatched.