Another mouse?

Question

This is both of my mic  

Is she pregnant?   I have 2 girl mice and were wondering how to introduce them to a new mouse im getting. I will be getting it from petsmart (And making sure its a girl so I don't have a fight or babies) any tips or advice? Also my  mouse looks is pregnant. I will put a picture on . The orange one looks a bit bigger.Thanks,

A mouse lover Kalee

Answer
Hi Kalee,

I can't tell from the photos if they are pregnant, but the surest way to tell is to wait 3 weeks (or so, give it about 21-23 days to be sure) from when they came home from the pet shop.  If no babies have happened by then, chances are she was just packing on weight as part of her normal maturing.  Mice are generally sold pretty young, usually 1-2 months old.  They will continue to round out until 3-4 months when they are really full adults, so a little widening is normal.  Mice come in all different sizes as well, so she might just stay larger than her friend, and that's okay, too.

My best tip for introducing a new mouse is to keep her separate from the others for 2-3 weeks before putting them together.  It's very, very easy to pick out a mouse at the pet shop who appears healthy, but is actually bringing home an illness they had just picked up from the other mice, and then you'd have three sick mice on your hands!  It's happened to me before, so I always recommend waiting before introducing, just to be careful.  This also gives you a chance to get a feel for that mouse's personality, and lets everyone calm down before being put into the stressful situation of getting new cagemates, since even just coming home with you can cause your new mouse stress for a few days.

Scuffling and chasing the first couple of days is normal, but just keep an eye open for any signs of aggression or violence.  Chasing is okay, for instance, but actual biting is a sign they should be separated.  If you need help figuring out if their behavior is normal when you put them together feel free to write me back.

Did you also need help telling genders at the pet shop?  It's always a good idea to double check the employee - two people being sure it's a girl are better than one!  :)

Those are really all of the tips I can think of right now, but if you have any other questions please let me know and I'd be happy to help out!
-Tam