Intelligent - African Gray Parrot

While comparative judgments of animal intelligence are always very difficult to make objectively, Psittaciformes are generally regarded as being the most intelligent of birds. African grey parrots are particularly noted for their cognitive abilities, which are believed to have evolved as a consequence of their history of cooperative feeding as largely tree-dwelling birds in central Africa.
Irene Pepperberg's extensive research with captive African greys, especially the one known as Alex, have provided evidence that these parrots are capable of associating human words with their meanings, at least to some extent, though these conclusions are disputed. Ambitious claims of language use have been made for another African grey, N'kisi, who has a vocabulary of around a thousand words and speaks in sentences.