The order Struthioniformes is a relatively small order of just five species, but includes some of the largest birds of all. Ostriches, emus, rheas, kiwis and cassowaries are all included in this order. These birds are all flightless and primarily eat insects and vegetation. Females of the order Struthioniformes lay their eggs in nests placed on the ground, but the males sit on the nest to incubate the eggs.