Via Paul Miller’s, 
, I was reminded that I saw the same birds flying around freely in Deventer last year. Apparantly, these birds enjoyed their freedom by hanging around the cages of their ‘jailed’ cousins in a bird park close to the Deventer railway station. The BBC has an article about that too, and apparently these birds seem to survive because of the string of mild European Winters.
The population boom has been put down to a series of mild winters, a lack of natural predators, food being available from humans and that there are now enough parrots for a wider range of breeding partners
I keep thinking of a certain Monty Python sketch.