Parrots are considered extraordinarily clever animals. Alex, the famous Harvard-based African grey parrot, had a vocabulary of more than 500 human words and answered questions and classified objects spontaneously. Scientists from the Max Planck Institute for Ornithology have shown that parrots exhibit a high level of social intelligence and cooperativeness. They readily help others, even when there is no immediate opportunity for reciprocation. Moreover, they reciprocate received favours and do not appear jealous, if conspecifics obtain a better reward than themselves. This further supports that they have evolved a level of intelligence comparable to that of great apes, crows and dolphins.