dominance in female mice

Question
Hi,
I got 3 female mice and I used to keep them in the same cage. They were supposedly all from the same litter. The smallest of them ended up growing bigger and stronger than the other two, and started to remove the fur from their heads to a point I had to remove her. Occasionally I would just remove the one that had it worse to recover, because she was being so aggressive with this that sometimes one of them would have scars. Now the other two are presenting the same behavior. I'm thinking about having 3 separate cages but I don't feel this would be really adequate. I don't think they are rejecting each other's presence because they sleep together, but I have pity in having 2 out of 3 mice with all patchy fur. What can I do to make them stop? Help!  

Answer
Hi Ana,

The behavior you're noticing is called barbering, and might be a learned behavior.  The other two mice likely learned it from the first dominant mouse, and she quite possibly learned it from her mother.  There may also be a genetic link since some types of mice seem more prone to it, but it's not quite clear yet.  Unfortunately, once a mouse has learned it, it's almost impossible to make her stop.

In most cases, it just means the submissive mice have patchy fur as you put it, but it doesn't actually hurt them.  However, you said one had scarring, which might have resulted from more violent aggression.  If you notice any boxing or chasing and squeaking, you should separate them.  I'm sorry to say that I have never heard of any other way to stop barbering except by separation.  The only other thing I can think of to try is perhaps putting more food in the cage, in case the dominance is aggravated by a competition for food.  I'm sorry, it's a very common behavior but there isn't much to be done about it.

Good luck,
Tam