hey folks. i just got these 2 cockatiels from a bird rescue. they are generally healthy and eat well but my female shakes her head constantly and is very aggressive. there is no nasal discharge or signs of parasites on her. she doesn't only bite me but occasionally bites her mate, which is a lot less aggressive. i don't know much about the history of these birds. i don't think they were handled much. they will set up on my hand if i go in gently. a couple of days ago, i gave them a misting bath w/ warm water. they seemed to enjoy that but the head shaking continues on my female. any ideas? thanks in advance!