You might not know it - I didn't - but we have a considerable parrot population in Stuttgart, and I am not speaking about the Wilhelma zoo. They live in freedom in Bad Cannstatt.
Where they originally came from is still a mistery. In 1984 the first of them has been seen, presumably it had escaped from a home nearby. Since they are quite social animals, it passed every day at the zoo in order to visit other fellow birds. As it seems, somebody pitied the lonely parrot and soon he found a female companion. This in itself also was a piece of luck because the sex of the parrot wasn't visible and they are also a bit choosy with their companions. So the little family thrived and procreated. Last time the NABU counted, there were 48 of them. In their country of origin, Mexico, there are just about 7000 animals of this species in the wild and our 50 parrots are the only population outside of the Americas.
Generally they remain in Bad Cannstatt, have also been seen in Feuerbach and Fellbach, though. It seems that the landscape reminds them of the Savanna in Central America.
As for food, there is plenty for them, even seeds which are definitely toxic for other animals like horses, don't do them any harm. There are no natural enemies (apart from the humans) and they preferably use the plane trees in the canopy roads in Bad Cannstatt, returning to the same places every evening.
Actually the plane trees were to be replaced by smaller maple trees because they were becoming too large for the street. Considering that the yellow-headed amazons have become an endemic species, after 3 generations, the plan to dig out the plane trees has been cancelled in favor of the parrots.
I think they deserved this after surviving this cold and hostile environment here, every year, don't you?