The Parrots of San Francisco

[Tobi]

I am only guessing here, but Parrots have quite long life spans don't they? If someone had released one or two -(or those had escaped) -then if something similar happened say five or ten years later, they could have bred.
There might have been a time when having Parrots as pets was particularly "fashionable"....but some escaped into the wild and obviously created more and more...