Caught wild mice; sex and babies?

Question
In January, we caught a young mouse (small, but not a baby) in a tender heart trap.  Since it was cold outside, we decided to keep it caged until it got bigger and was warmer out.  Later in February we caught an adult pregnant female.  Again, not being able to release a pregnant female into the cold, we kept her until the weather got warmer too.  Since we only had one aquarium and they were the same species, we put them together.  We saw five "pinkies" not moving under the wheel right before we left for vacation.  When we got back, the babies were gone.  We assumed she ate them since she was recently caught and probably scared.    They got along great and are two peas in a pod.  Since they were so amusing and cute, we decided to keep them.  While cleaning their cage today, I found two young ones.  They were small but had fur and their eyes were open and attached their mouths to the mom's bottom.  I had not cleaned their bed before because it always seemed clean and I didn't want to upset them.  Could the tikes be from that first litter, or are they recent?  How can I tell if they are male or female?  The one that the babies did not attach themselves to has a swollen bum.  Should I separate them?  Could both adults be females?

Answer
Dear Tarcey,

You have a male (swollen bum = testicles) and a female. You are lucky you don't have a hundred babies! If the babies you found are still nursing, but their eyes are open, they are between 2 and 4 weeks old. They are no longer called pinkies when they have fur.

She ate the babies because they were dead. Otherwise they would have rotted and been unhealthy for the live mice. We don't know why they died-- whether she abandoned them because they were unhealthy or she was uncertain that it was a good place to have babies, or if they simply died in the nest and she moved them.

I assume these mice are still quite wild and you intend to release them? If so, wait another three weeks, since the babies might have been only two weeks when you found them. If you don't either release or separate them, you could have another litter from this mom anytime now, and new litters (if both are female) from the new babies in just over a month!

Here is how to sex babies. They don't have the swollen bum when they are small, but there are two differences that you may be able to see if you look at their underside through a glass bowl (I'm assuming they are not tame enough to handle and turn upside down and examine).

1. You may be able to compare the distance between the anus and the papilla-- that is, both males and females have a piece that looks like a penis, that they pee out of. It is farther in the male.

2. You may be able to see that the female has nipples and the male doesn't (although that's hard to see on already furred, baby mice).

The link uses the correct terms for  female mice (one doe, two does) and male mice (bucks), just like deer!

http://www.thefunmouse.com/info/sexing.cfm

If you are thinking about keeping them, only do it if they seem happy in the cage and do not try to escape. If you let them go, do it over a mile from the house, or they may return. Find a meadow or forest, and leave them some food and, if you can, a cardboard box with bedding and food and two small entrances; you can pick up the soggy box in two weeks, when they will be gone.

Best of luck!

squeaks n giggles,

Natasha

<:3  )--~