Behavior changes in a cockatiel--any suggestions appreciated

I'm at my wits end.
I have noticed some disturbing behavior changes in my 7 year old cockatiel. About a month ago he stopped being interested in his favorite toys, stopped singing, and started preening to constantly. It got me worried so I gave him some new toys and took special care to enrich his enviornment. Not only did this not help, it's gotten worse. Yesterday I woke up to find him digging a wound into his shoulder. I have had birds my whole life and have NEVER seen self mutilation in a cockatiel.
Before you ask, yes he has seen a vet. She looked him over, couldn't find anything wrong and then suggested I do what I have already done (new toys etc.) Also, he is not a cage bound bird. If I'm home he's out getting treats and singing with me--and I'm kind of a home body so that is alot of time. The only change that I can think of that occured around the onset of these behaviors was a switch from seed to roudybush pellet food. He has been on this brand of pellets before without any adverse affects to his behavior.
I've had luck using companioning with other animals, but have always avoided that method with birds as it can make theim unfriendly with humans. I'm considering it very seriously in this case though. Has anyone tried companioning a cockatiel with another bird, or have any other suggestions? Any help is greatly appreciated. He used to be such a happy little guy, this is really breaking my heart.

 

One thing I forgot. Before he came to live with me he was my sister's bird. She was a model bird owner for years, but eventualy did grow out of him. My mom became worried that he wasn't getting enough attention, so she brought him to live with me.
He and my mom had a really special bond, and she visited recently. He really perked up when she was around. The shoulder digging incedent happened about two weeks after she left--but I'm starting to wonder if they are connected. I'm tempted to wait it out and see if he readjusts to not having her around all the time, but I'm super worried that this will become an unbreakable habit that I have to battle for the rest of his life if it's not nipped in the bud.

 

i would switch back to the seed you were using pronto hun.
often the clue to drastic changes is the 'it started after i ......' or 'it happened after......'.
i know you have had luck with the pellets before, but like any commercial pet food, they can change the formula without saying at any time.
if you do change back, you could also try stuffing his seed into things like pine cones (if they are safe for burdies) so he has to work for his food. heck you could do that with the pellets i suppose. hopefully if he has to spend a good portion of the day obtaining his food, hopefully he wont be too interested in self mutilation.
but i really would try switching his food back hun
good luck and let us know how he does! xx

 

Thanks for the suggestion. I hadn't thought about a possible formula change.

 

Have you tried a peacock feather bird toy or a rope for him to preen instead of himself? good luck

 

That was one of the first additions to his toy collection. He's got a couple feather preening toys as well as a tear-it-apart paper toy. Thanks though.

 

Yeah I suspect the change in diet may be the causitive factor. Switch back and observe.