• identical twins;
  • genetic identity;
  • emu;
  • Dromaius novaehollandiae


We report on the first established case of identical twinning in birds. The occurrence, genetic identity and subsequent development of identical emu (Dromaius novaehollandiae) twins is described, and comparisons drawn with single chicks hatched in the same season. The twin-bearing egg, significantly larger than any other egg in the same clutch, was artificially incubated and hatching assistance was necessary. At hatching the female twins were small, but their combined weight approximated that of a single chick from an egg of equivalent weight, and by 18 months of age they were near average in size. DNA analysis of blood collected from the twins showed a complete match with 22 bands per sample larger than 3.8 kb. The estimated probability of this occurring by chance was 1.0×10-13 in two unrelated emu and 1.0×10-6 in siblings, indicating a high probability that the twins were identical.