It's just his neck area now, and I'm calling the vet tomorrow (today is a holiday in Canada).
I don't think it's anything serious - my other two aren't doing it, so I think I can rule out mites. He's also acting PERFECTLY normally. He has been eating more eucalyptus than usually lately, but that's the only "odd" thing. He loves his bird family and has plenty of toys. My theory is that it's too hot and dry right now. The building turns the heat up like crazy since it's freezing outside and my babies haven't had a decent shower since the bathroom is being redone.
He's just molted, so maybe the feathers are growing back in and are itchy?
I'm doing extra spraying now and have put extra bits of greenery in the cage (though he won't touch anything but lettuce, euca, cilantro, and sometimes apple).
If anyone has any suggestions, I would be so happy to hear them.
Thanks so much to anyone who's bothered to read this far!