My 4 year old female was an "only dog" until last June. Prior to getting another shepherd, a male pup, she was always pretty quiet and rarely barked. Since Natty was introduced into the family, she has become quite vocal, barks at outside sounds, alerts to delivery trucks, and makes other vocal communications, especially when she is playing with him. (She has also started barking whenever she hears my Smartphone "ring," so I've been working on teaching her that this is a sound she should ignore.) With her the vocalization isn't out of any fear; I think it is more about getting attention and asserting her place in the household.