While comparative judgements 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.[citation needed] Although there exists a great deal of debate as to just how well these birds actually understand the meaning of the words they speak, there is little doubt that Greys and other parrots (especially macaws and cockatoos), along with corvines (crows, ravens, and jays), are highly intelligent in comparison with other birds.
It is widely believed in the parrot-keeping community that Greys understand their human companions at various human intelligence levels. For example, some believe that a young Grey (under a year) has the equivalent understanding of a human toddler and the cognitive ability of a 6-year-old human child.
Many greys are excellent talkers, with a capacity of over 1500 words. They don't repeat all words they seem to favour a few and just learn new ones and say the words they know at random along with household noises such as the telephone ,doorbell or microwave, often so well that they confuse their owners! greys have a unique capacity for putting their words and sounds into the right context as opposed to simply repeating them, which shows their intelligence, Our grey Reggie will call my son and tell him to go and put on his shoes as we are going in the car simply when he hears me pick up the car keys!
