Animals routinely experience mental illness. Especially the ones that can't find a mate. Some even descend into gay necrophilia. I even read about a duck that was trying to gay rape another duck. The first slammed into a wall and died. The other raped it's corpse. So add murderous, or at least morbidly reckless. Psychological imperatives are just like biological ones. If you don't do them, shit goes wrong.