My fiance had our parrot Casey for 8 years, 7 before I met him. for the past year since I've met them Casey has begun favoring me over him, despite him raising her since she hatched. it's now gotten to the point where she's hostile and aggressive towards him, head bobbing and lunging to bite him if he even stands up or moves, she won't let him come near her. I've been ignoring her when she screams and giving her attention again once she stops or starts chirping instead to reinforce positive behavior but she still hasn't stopped screaming. this has been going on for the past 2 or so months. she's also begun screaming for attention if I don't give it to her 24/7, and screeching at the sight and sound of my fiance. she's otherwise happy and healthy, but has always been an anxious bird. is there anything we can do to deter her aggressive behavior so she's at the very least indifferent towards him? we are at our wits end.
It is fairly common for quakers to change allegiance. Our quaker, Bonnie, tends to target my husband aggressively much more so than myself. But some days it is the opposite. She tends to keep us guessing.
If you search through the posts on this Forum you will find quite a lot about agressive behaviour - even my posts about our quaker Bonnie might be useful.
Meanwhile you are doing your research here, perhaps you could try withdrawing from Casey altogether for the time being and let your fiance be the "good cop". He could be the one to give her treats. If possible you could arrange a certain time for her to come out of the cage and ensure you are not around at all (you could pretend to go out and your fiance could let her out while you are gone). He could start with 5 mins and give her a favourite treat for appropriate behavour.
When Bonnie is aggressive I sometimes just open the cage door and completely ignore her/disengage from the noise and aggression if possible. That way I am not engaging with the attention-seeking behaviour.
It's a very difficult situation and we still struggle with Bonnie's behaviour on a daily basis, however, the key is to be consistent in your responses (both you and your fiance) and try to remember that it's a quaker personality trait that is quite common and it doesn't mean she hates your fiance. Try not to take it personally...