Could the reason be YOU? Companion parrots react to how we humans feel when we approach them. They pick up on if we are stressed, nervous or unhappy, so its best not to approach them when we are nervous, stressed or unhappy. They will sense it and this will result in fear and apprehension. Parrots don’t have much time to think and are more likely respond with a quick bite.
Another way we can cause companion parrots to bite is if we use our hands for punishment. if we use our hands to shoo them away or even worse to throw objects towards or at them in order to “shut them up” or stop a behaviour we consider bad and the next time we want to handle them after that, they won’t know whether our hands approach them in a friendly manner or to punish them or to drive them away.
Also, if you only pick them up with your hands or arm to put them back into the cage, they will soon learn to dislike your hands or arms very quickly. This being said, in order to prevent them from disliking your hands or arms use them for fun things, like walking around the house, giving scritches/tickles, healthy treats and talking to them this will help your parrot realise that your hand or arm is not only used for putting them back in their cage. One of the most important things is to teach your parrot that they have nothing to fear of your hands.
In many cases (particularly in cases of poorly socialized or abused birds), it is self-defence. They may have learned that hands are something to be scared of — because people might have attacked them) in the past, waved their hands in a threatening manner at them, used their hands to throw things at them … Once that happens, birds will associate hands with something bad. We use our hands for self-defence. Birds don’t have hands — they use their beaks. The trick is to teach them that hands are something good and only to be used for preening them, holding them, giving them healthy treats. Never ever use your hands in a negative way. Be aware of how your hands are perceived by your parrot. Always approach your parrot with your hands slowly, in a non-threatening manner. The more your parrot learns to trust you, the less likely you’ll get bitten.
The more scared or startled they are, the harder they will bite. Parrots are prey animals and have learned that predators can approach them at any time, sometimes they may not realise that it is their human that is approaching them quickly, and they will bite to fend off a potential predator.
Even bonded parrots will bite, but mostly only to let you know they don’t like what you are doing and their bites are generally gentle and don’t hurt. However, if you ignore this “gentle” warning, the bite becomes more forceful and painful.. Playtime and exercise: Parrots use their beaks for climbing and holding on to things as they move about. These bites are usually not painful.
Reacting to a bite…
If your parrot is sitting on your hand while biting, drop your hands a few inches, this will force your parrot to focus on getting its balance back and they’ll usually release their grip on your finger. Place your parrot on the floor or on a play stand. . The worst thing you can do when your parrot bites or is trying to bite is to scream, yell or pull away. Such reactions will only reinforce this behaviour. Instead, you should find ways to prevent being bitten. For example, take the time to learn your parrot’s body language. Do they pin their eyes, flex their wings, fanned tail feathers, fluffing up their feathers to make themselves look bigger and crested parrots such as cockatoos will put up their crest for the same purpose, before they bite etcetera? Most birds have a common signal to tell you they’re getting angry. Learn these signals and the two of you will be able to come to a harmonious solution much faster.
Gaining your Parrots trust
You will have to spend some time working with your parrot. Talk to him calmly. Understand that your parrot may become aggressive as long as he or she doesn’t know and trust you. Spend lots of time making friends with your parrot in a non-threatening manner. Don’t approach them with your finger or your hand until a bond or understanding has been established, and even then, only when they are okay with it. In fact, don’t force physical contact at all. Gain their trust by talking and spending time interacting with your parrot in a manner that doesn’t put any stress or demands on them. Offering healthy treats also helps to gain trust, but the goal is to have the parrot come to you to get the treat, rather than you breaking through their comfort zone barrier to get the treat to him or her, which may result in a bite.
You should accept your parrot on his or her own merits. The parrot that you have may not be the cuddly companion you anticipated, parrots are not domesticated animals like cats and dogs, they’re essentially still considered wild. However, every parrot will have personality traits that you’ll really enjoy; whether it is singing, talking, or just being a companion who likes to sit near you while you are watching TV. Enjoy them for what they are, in the end you may be surprised about how strong a bond you both have forged.
The rule of thumb is, If you want to see that behaviour repeated, reward it! If you don’t want to see that behaviour again, ignore it.
For further reading, the following link may be of interest
https://birdtricksstore.com/blogs/birdtricks-blog/parrot-training