My budgie (Nua) is a biter. No signs and nothing. One moment we're playing with her vegetables, then she goes ham onto my finger. No clue why. I have spent about 40 dollars in chew toys and all types of different shredder type toys. Let her out of the cage the entire time I'm at home and she's willing. Food, water, and millet. I don't know if it's hormones or something, because I notice a couple pin feathers sticking out.