Newly aggressive GCC

[AlyAngel80]

I've had my first green cheek conure Coco for about three years. After much consideration, I decided to get a second green cheek and have had Rupert for about three weeks. I was fully prepared to house them separately for an extended period of time (if not forever) but they hit it off very well. They have never shown any sort of aggression of any sort toward each other. So, for about two weeks now, they have been living in the same cage. Rupert is five months old, was hand raised and had been very socialized and had always had a very sweet disposition. In the last few days, he has been very aggressive towards me. He comes out of his cage just fine and doesn't get aggressive right away but he'll get super fluffed up, fan out his tail feathers, and bite my hand to the point that it bleeds. It's like he'll go along just fine, not having any issues and suddenly turns and gets mad and aggressive. I don't let him on my shoulder anymore because the first time he did this, he latched onto my ear and made it bleed. I never use any sort of negative reinforcement but as soon as he shows aggression, I put him back in his cage. I always use a calm, level voice and praise him when he steps up, takes treats, and plays. He never gets aggressive toward Coco and his mood swings never seem to be related to whether or not she's getting attention.
I really have absolutely no idea what sets him off or what to do about his behavior issues. Any advice would be greatly appreciated.
I should mention that I use 'he' and 'she' freely. Neither bird has been sexed so I don't know for sure.

Thank you!!

 

[MonicaMc]

It could be something as simple as a shadow, the reflection of something, something happening outside, perhaps the way you moved, something on TV, or any other number of things. Birds are fine-turned into their environment and any little thing can set them off. Maybe he's getting bored or he's tired.

You might try setting a timer and see if there is a specific time once out of his cage that he starts acting aggressive, and once you've figured that out, put him back at his cage before that time.

Likewise, you can try teaching him new behaviors that he may enjoy doing, such as turning around, waving, spreading his wings, or something else.