Chromosome banding studies allowed us to distinguish the sex chromosomes of the emu (Dromaius novaehollandiae), American rhea (Rhea americana), and Darwin’s rhea (Pterocnemia pennata). In each species, we identified the Z chromosome which is very similar to a carinate Z, and the slightly smaller W chromosome. Contrary to the uniformly heterochromatic carinate counterpart, the ratite W chromosome is euchromatic and retains remarkable banding homology to the Z chromosom