Greater rhea breeding is polygynandrous and heavily male-invested. A male displays to a group of females, mates with them, and prepares one shallow nest lined with vegetation. The females lay into that nest over a period of days, then move on, often laying subsequently in the nests of other males.
The result is a communal clutch. Counts of twenty to fifty eggs in a single nest are routine, and much larger totals have been reported. The male incubates for roughly six weeks, defends the nest aggressively, and then leads the chicks. He will chase off other adults, including the females that laid the eggs.
A detail often missed is that eggs laid outside the nest are common. Females sometimes drop eggs on the ground nearby, where they rot, and some observers think these attract flies that the newly hatched chicks then eat, though that explanation is not well established.