Each pet bird has his/her own personality and may react differently to the same situations.
Some birds will bite the person nearest them or even another bird when someone new approaches. Called displacement, your pet is protecting itself from the newcomer. Sometimes birds will nip their mates to encourage them to fly away from the newcomer as a protection. Then they will advance on the intruder. Don’t allow your bird on your shoulder when this happens especially if it is habitual.
Young birds often use their beaks to explore or test their surroundings. This may include your fingers. You can discourage this sort of biting by offering your bird a toy. A firm “No” can work too.
My cockatiel Tweety is usually calm and loves when I talk to him. He will often answer with his usual vocabulary. However, he is territorial and is not happy when I touch his cage or any of his belongings – a case of biting the hand that feeds him. If your bird reacts this way, you may want to use a perch for your bird to sit on to encourage him to leave the cage while you clean it or refresh food and water. Try not to make eye contact as this can signal aggression to your bird.
If something frightens your bird, s/he may bite in self defense. Look at things from the bird’s perspective. There are times when something they see upsets them and they bite out of fear.
Try to distract your bird from unwanted behavior. Toys, teaching a trick, showering or bathing, all these can be used without punishment that doesn’t work anyway and can cause your bird to mistrust you.
Birds that come from a home where they were abused will often use biting to defend themselves. Learning to trust can take a while for a bird that was exposed to such a situation. Training your bird to use a perch helps as well as offering treats for acceptable behavior.
Never tease or hurt your bird in any way – it will only encourage unwanted behavior to continue.
With lots of patience and loving care, your bird will learn to trust you and stop biting.