Breeding behavior is rarely so aggressive, although it can be perceived that way by we humans.
Tell me more about how you interact with her every day. Does she spend any time out of cage?
Are you sure she's a "she" ?
If you try to see things from this macaw's point of view what you'd be feeling is a tremendous sense of fear and insecurity. Having been with one person since she was a chick, she not only bonded as a baby, but as she grew into maturity. To suddenly end up out of the surroundings she was familiar with, felt safe and secure in, had a routine or pattern established, learned all the sounds and events in - she's not sure where she is or why she's not "home".
What seems like sudden acts of aggression by many birds isn't necessarily unusual and you can probably change it. No matter what started it, your bird is enjoying a sense of power and control at this point. They have discovered that these actions are getting a response. Macaws and most other parrots are remarkably smart and learn quickly despite how we might perceive it. Your bird is seeing how far they can go. The trouble with this is that many birds end up cage bound as a result of owners becoming afraid of them and that encourages even more behavioral problems.
It's very important to keep in mind that when a bird suddenly changes in personality and becomes aggressive or reclusive, it's imperative to have a vet evaluation to rule out a variety of possibilities in the way of illness. Remember, a bird that's weak or injured is at risk for predation. Even though your bird is perfectly safe, their instincts don't know this and will perhaps overcompensate by becoming defensive.
Once a full blood panel, crop and vent swab/cultures are done on top of a good physical exam and illness or injury is ruled out, approaching it as a behavior issue is your next move.
When the bird lunges or bites, issue a "don't bite" order in a firm, but not raised voice and then turn your back. Give silence a minute and then turn and with a firm voice and no-nonsense face, take the bird out of their cage.
If you're concerned about biting, keep reminding yourself that once the bird is up on your arm, if they bite you can provide an ‘earthquake', a sudden vibration of your arm enough to distract them from the bite, but never enough to throw them off balance. Remember, scaring them isn't a good thing. They are not likely to go back to biting your arm and you can probably carry them around for some time like this.
We also don't discourage the use of padding. Just not the use of gloves. Gloves don't encourage the respect of human hands and this is one of the things you're aiming for.
However, cutting the toes out of a clean pair of old, thick socks and sliding them up on your forearm or under shirt sleeves can certainly take the sting out of a bite by a larger bird and give you more confidence. When you stop reacting to the biting, the bird is more likely to stop using it as a control method.
Carry your bird around to different rooms, which gives you even more control because they're not used to the surroundings and become dependent on you to take care of them.
Always hold your bird below your own eye level. A bird at your eye level is a bird who thinks they can gain the upper hand (or upper perch).
Be aware too. We can't possibly know what the bird sees all day or how it perceives it. One client couldn't understand why her entire aviary suddenly became afraid to leave their cage and often huddled in the far end. With an on-site inspection we noticed this very good and caring owner had set up a t.v. to play a loop of video for their entertainment while she was away for the day. She even went so far as to find nature videos. Upon closer examination we found the source of the problem. The videos were all laden with predators! From sharks to lions - snakes and raptors (meat eating birds of prey) - her birds were terrified.
Once the videos stopped (she eventually opted for non violent children's cartoons), it took a while, but the birds returned to their normal, friendly personalities.
We also have to consider that a bird might have seen something we didn't see outside the window. Hawks? Neighborhood cats? Even airplanes can be intimidating.
During molting season (which is now) a bird may become a bit more aggressive and self-protective as well. They lose some important feathers at this time and their flight (if they were fully flighted and in a natural environment) would be slightly impaired. During a molt they don't travel as far from their immediate home territory as they might otherwise (in the wild). This instinct remains and can effect their behavior in their human home. Even in a bird that is clipped and perhaps has never been fully flighted.
Extra gentleness, patience and insistence on getting them out of their cage and keeping with routine are very important. It's far too easy for a bird to become cage-bound if the human allows it.
Take a look here for more tips on interactions, ideal feeding and how to step by step deal with a screaming, biting bird
http://www.4animalcare.org/birds.html
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Animal Rescue&Care Org Owner; Animal Care author; Animal Behavior Consults.;Cert. Avian Specialist;