Someone on one of the other forums I visit posted this link, which I thought was quite funny. It's sourced from the writings of Pliny the Elder, Isodore of Seville and Sir John Mandeville, and gives the medieval explanation of the parrot:
The parrot is a bird found in India that can be taught to speak like a man. It learns better when it is young, but if it will not learn one must hit it over the head with an iron bar. It can say ave (a greeting) by nature, but must be taught all other words. Its beak is so hard that if the parrot falls from a height it can break its fall with its beak. Parrots are colored green with a purple-red collar; they hate the rain because the water makes their colors appear ugly. There are two kinds of parrot: the kind with three toes have a mean disposition, but the ones with six toes are gentle.
http://bestiary.ca/beasts/beast235.htm
So, if your parrot is being a grumpy feather-butt - it's probably because you failed to check the number of toes when you took them in.