Why do rheas ostriches emus look so much alike?

Rheas, ostriches, and emus resemble each other due to convergent evolution, where different species independently evolve similar traits as adaptations to similar environments. These Flightless Birds share a common ancestor, but over millions of years, they adapted to their specific habitats and lifestyles, leading to similarities in body shape, size, and feather characteristics. Their similar adaptations help them survive in open grasslands and savannas, where they rely on running for escape from predators.