Those birds then escaped or were released. Most of the flock is now native-born. They've completely adapted to the area. Besides being familiar with local bird feeders, the flock knows which trees they can eat from. Getting enough food isn't a problem, nor is the weather.
Wild parrots can endure cold.
I believe that the greatest danger they face is from human beings. There are folks who oppose the presence of any and all non-native species. There are problems within the local ecology that are the result of non-native species, and with increasing frequency the issue is turning up in the media and on the agenda of various government agencies. While the issue should be studied, it should be studied fairly and with a good heart. It would be wrong simply to say that everything non-native must go.