I've had a U2 for about 6 years. He is a rescue and I am not his first owner. Overall, he's a good bird, but sometimes he will bite that (seems) so come out of nowhere. He is very playful and typically in very good spirits, but every 4-6 months, I'll get a very aggressive bite. I don't react, typically placing him in his cage without any further comment. The bites typically break the skin and can be quite painful. I have noticed I'll get a bite around spring when he is particularly hormonal, which can be expected, but any other bite seems to be very random. I have tried a sleeping cage, which did help for a while, but recently while moving him from his sleeping cage in the morning, received a bite twice within a single week. I will get a warning sign after he is perched on my hand and gives me a "stink eye" kind of look a moment before launching into a bite, always landing in the thumb area. I was wondering if anyone has experience with this who have any advice to share, inclusive of a training exercise I could try, perhaps? I am his only handler and the last thing I want is to somehow be unknowingly promoting this vice. Please help.