Keeping wild mice until it is warm enough outside

Question
Our home has recently been invaded by a brown mouse who turned out to be pregnant. I have an open crate for my guinea pig and I think our guests are in mousey heaven. We have managed to catch three babies using humane traps but are having real difficulty catching what we believe to be the last baby. We have set up a home in a small vivarium and are feeding the captured babies with hamster and guinea pig food. It is so cold at the moment we haven't the heart to put them out. We seem to have lost the mother mouse, we can only hope that the babies were ready to be weaned.
Q what is the best way to provide water? We are using an egg cup at the moment. Q They don't seem to be interested in fresh food, should we continue to provide it. Q Is there any food that is essential for their development. Q Will they inter breed? Should we separate them (if we can work out which is which). If so is it a matter of urgency? Q Is it fairer to the mice to set them free? Q Any ideas how to catch the final baby? He/she is so quick.
We keep the babies as quiet as possible as they are extremely nervous. Q Is there anything we could provide to ease their nervousness? They have a place to hide and paper bedding on shavings.

Thanks Clare

Answer
Dear Clare,

Babies are weaned at about three weeks. I don't know if you know when they were born. Anyway if they are eating solid food, they are OK (you are sure they are eating, right?). If they don't eat fresh food at all, they don't need it. Mice and other rodents don't like the same things, so don't expect them to eat what your guinea pig did.  For instance, a big leaf of lettuce may not interest them, while they may love some and not other of the leaves in a package of baby greens/herbs. Avocado is a huge hit but *not* the pits or skin (I had a cage poisoning once with a pit.. : (((((  ). But really they don't need anything more than the dry food.

One way to give them water, which lasts more than the two minutes it takes them to fill the dish with litter, is to soak a bit of hard bread such as rye crisp in water or rice/soy milk and place it in the dish. Another thing to do is just give them cucumber, or a sweet orange or apple slice, for liquid. But juicy foods do spoil, so you will have to pay attention (which might mean finding it) and change it once a day. The most important thing about water is that the container not be big enough for them to fall in and drown. An egg cup is actually pretty big.

If they are still pretty young they might do well on that soy or rice milk. Soy yogurt is a hit too. Some scrambled egg is easy to eat and packed with protein.

If you only have babies, male mice can't mate until they are 6 weeks old. It takes 3 weeks for gestation, so even if you didn't get them outside until 7-8 weeks, they girls would still have time to make a nest for the babies. Or you can separate them, which can't be easy!  The best way to tell the sex of a nervous mouse is to put it in a glass container and look from underneath. Boys don't have nipples, but it can be hard to see them on the girls too. And little boys don't have the mature dropped testicles that make it easy to tell at a glance on an adult mouse. But this link should help:

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

If you can get them all in the glass bowl at once it might be easier to compare. Don't do it until it is necessary, as the younger they are, the harder it is to tell. They won't necessarily mate at six weeks either; that is the earliest for a boy (girl is 4 1/2 weeks). Pet mice squeak a lot when they mate (the girls run away squeaking as the boys chase them... like in elementary school) but wild mice might not, because it would attract predators. Lots of chasing is a tell-tale sign.

I keep the mice I catch until it is warm enough to let them go, too. It seems only fair. Then find a nice woody spot or meadow. With an adult I would say over a mile away, since mice have a range of up to a mile, but these babies of course didn't. There are a number of different kinds of humane live traps out there. Baby four might have witnessed its siblings get caught in the one you have and has learned to avoid it or has learned to get out (I once had a trap that turned into a mouse buffet, as the mice, smaller than the trap was apparently intended for, basically lined up and went in, ate the food, and left unharmed). If you have been using a havahart trap it may be getting in and out; here is a trap that I haven't tried yet which seems useful:

http://www.google.com/products/catalog?client=safari&rls=en&q=smart+humane+mouse

What I love about it is that it instructs you to take the mouse to where mice are needed!

Nervous mice like quiet rooms without a lot of light, at least at night. They need safe, small places to hide, like a little box; lots of nesting material, such as tissue; and empty toilet paper rolls are a must. Your little guys also definitely want a wheel. They will be strong enough to run on a wire hamster wheel if you don't have a mouse wheel. Also I'm sure you know mice are nocturnal, so you shouldn't expect them to come out during the day or when the light is on.

Best of luck! Don't grow too fond of them, though; as long as they are still nervous, try to escape, and don't let you hold them, they do want to be released when the weather is warmer.

squeaks n giggles,

Natasha