Ostriches have been around for a long time and most experts think that they first evolved about 120 million years ago. Return to Menu Rheidae Rheas are the South American version of the Ostrich and on the Pampas they fulfil a similar ecological niche, feeding mainly on vegetation, but taking insects and small vertebrates when possible. Both species tend to live in medium sized flocks of 5-50 individuals. Rheas, like Ostriches, are adapted for running as a means of escaping predation and they run very quickly. Their wings are proportionally larger than those of other ratites and they use them to help them gain speed and stability for quick sharp turns.
Rheas travel freely for most of the season, but males become territorial in the breeding season.
This begins with them evicting the other males from the flock. Younger males leave first, then the older males fight using their heads and necks until on dominant male emerges. He chooses a territory near some water and scrub and makes a nest there. After mating the females start laying and as soon as some eggs are laid the male starts incubating them and becomes very broody and protective - to such an extent that females wishing to lay more eggs cannot get to the nest and must lay them nearby. Many eggs are lost this way.