Could be a number of reasons, but at 5 years old could very well be hormones, my 5 year old has just started plucking slightly too. you need to sit down and take a look at what's changed first in the house, list them down, and gradually try and change things back if you can. If the dog is an issue can he be kept in a seperate room as the parrot for a little while see if that helps? maybe they have given more time to the dog and that caused the parrot to pluck? It's very hard to say, could be any of a number of things. I would go back to basics now, make a list of what's changed and see if they can be correct, see if that can cure the problem x