The capacity of a parrot species to mimic human speech, ranked from exceptional (African Grey) to limited (most conures and cockatiels).
Talkability is partly anatomical (some species have a syrinx better suited to consonants than others) and partly social. African Greys top almost every ranking — Dr. Irene Pepperberg's 30-year work with Alex demonstrated genuine context-aware vocabulary use, not just mimicry.
Other strong talkers include Yellow-naped Amazons, Indian Ringneck Parakeets, and Budgerigars (which can develop vocabularies of 100+ words despite their small size). Conures, cockatiels, and macaws can learn a handful of words and short phrases but rarely build large vocabularies.
Within any species, individual talkability varies enormously. The best predictor is how much time the owner spends actively talking to the bird — and whether the bird hears the same word repeated in context, day after day.