Caught house mice, possibly pregnant female?

Question
QUESTION: Hello, I was hoping you could help me with my house mice. I have recently caught 4 house mice (One male who I keep in a separate box and three females) and I was planning to wait until summer before releasing them for the best chance of survival (Although they seem quite happy in their new home so far!) however one of the females is very big and looks very bloated in comparison to the other two. I can't be sure if she's actually pregnant since she doesn't like to be handled yet so neither I or a vet could feel her so is there any behavioural signs which would hint at pregnancy? Also what should I do about her housing situation? She stays with the two other females in a medium sized plastic box (Which has very good ventilation, I've checked!)with one food bowl, one water bowl, a tube, two wooden blocks and a large wheel. All three of the females refused to use the wooden mouse house I bought, preferring to sleep in a pile in the corner of the box with lots of bedding. Should I separate her from the other two and give her a different house or will that stress her out too much? And if she's pregnant is there any tips to let me help her raise her young in a good environment? Thanks in advance!

ANSWER: Hi Kern,

The best way to determine if she is pregnant is to wait three weeks.  The average gestation time for a mouse is about 21 days, give or take one or two.  Unfortunately, there are no other definitive signs that couldn't be attributed to her new situation or adjusting.

It sounds like they have a pretty good setup!  The number one thing for a pregnant mouse momma is to avoid as much stress as possible.  If the other mice pick on her, you may want to remove her, but otherwise it would be best to leave her be.  If pups show up, she will keep the nest they live in very clean all on her own, so all you have to do is make sure the rest of the cage is tidy every now and then and that there is plenty of food and water.  Mom really does everything else on her own!

Since you are planning to release them, the less interference you give, the better.  Just be sure that once they hit around 4 weeks old and are getting to be independent, full-sized mice, that the males are separated to prevent future babies.  Be sure not to put any boys from the group in with dad - male adult mice can be very aggressive toward other males.  Also be sure that before you separate them you make sure they can drink on their own - once one mouse figures it out, the rest follow quickly!  Speaking of water, you may want to try switching to a water bowl once the pups can walk around so they do not wander into the bowl and accidentally drown.  There aren't any water bottles in nature, but their instincts will take over once they get into the wild, and it's better not to take any undue risks.

Hope I helped, and let me know if I can do anything else!
-Tam

---------- FOLLOW-UP ----------

QUESTION: Sorry but now they're born I was wondering if it's normal to hear chirping from the nest for the first two nights but not hear anything the next?  Could she have killed and eaten them because she didn't feel safe or could they have just give quiet? I'm hoping they're okay since the mother and one nanny only time out of the nest for food but if she gas eaten them then could there be anything I could give her to aid her recovery or cheer her up a bit?

Answer
She may just be getting better at taking care of them - as they grow they will start sleeping more regularly and needing fewer feedings from mom over the course of the day.  I think if mom is spending that much time in the nest, it looks hopeful that they are alright!

If she did eat them, which unfortunately sometimes does happen with a first litter or a mom who does not know what to do, there isn't anything you need to do except be sure she still has plenty of healthy food and water available.  It can be very sad, but it is a natural thing that sometimes happens in the wild, too, and the best thing for her is for things to continue as close to normal as possible.

Congratulations on the litter, and I hope they are alright!  Keep me updated if there is anything else I can help out with.
-Tam