New companions!

Question
Hi there! I had two lovely little female mice, tonight one unfortunately passed away. I'm looking to get 2 new companions for my remaining mouse! Do you have any suggestions for getting them acquainted, things to watch out for, etc?
Thanks a ton!
- Allie

Answer
Hi Allie,

I'm sorry for your loss, but I am very excited that you will be getting two new buddies!  If the surviving mouse is having a tough time grieving, it would be a very good idea to isolate the new girls for, if possible, 2-3 weeks before introducing them.  Grief can lower the immune system which can make her more vulnerable to anything new mice might bring home from a pet shop accidentally.  Also, this will give her a better chance to get to know them when they are all introduced and pick a pecking order, so to speak.

Really the biggest thing to keep an eye out for is aggression.  Chasing and even some squeaking is normal at first as they get used to each other, and should settle over a day or two.  Real aggression, however, is serious and cause for separation - signs include biting, signs of bites (blow backward on the fur to look for scabs/spots), tail rattling (buzzing the tail against something hard as a warning), or boxing (standing on the front legs and "punching" outward - this is not harmful but is a sign a mouse feels cornered enough to be risky for both mice involved).  To avoid these, it may be helpful to change the bedding before introducing so it is a fresh start to all, and to either remove or add cage toys and hides as needed if they squabble too much over them.  Most of this is really just worse case, though - with supervision, most introductions go well and, once dominance is safely established, everyone becomes friends.  :)

I hope I helped, and if you have any other questions along the way, just let me know!
-Tam