Broke college student taking care of a wild (baby?) mouse

Question
A couple of days ago while getting Pho a friend almost stepped on a small mouse that was laying half frozen in the middle of a sidewalk. We considered walking away for a while, but then decided that was wrong and picked him/her up and brought them home. Now a friend and I are taking care of it (we call him a him), but it's hard on a budget. I'm really broke right now because it's my first time not living with my parents, so I  ant really afford to buy him nice things. Right now he's living in a see through shoe box (the plastic ones you buy at the store- they're a little bigger than normal shoe boxes), it's a little small but he's doing well. Last night I added a half second floor with cardboard and he seems to like it, and I feel better because he has more space and it's around the size of a normal cage for one hamster.

My problem is that he keeps trashing it and I don't know how to take care of him! We bought him goat milk and put it in a bowl in there with his seeds. He drinks a little bit, but almost always makes a huge mess! He poops everywhere and always tries to escape and it makes me sad because I think he's miserable. We can't let him out yet because it's still freezing outside, but plan to let him go after a month (even though I'm starting to really love him). What are things we could do to prepare him to go back out? Also, what would be a good cheep flooring? Right now we have soft toilet paper on the floor and a cup filled with toilet paper that he burrows in. What could I do to make him happier, without buying him things? We were considering getting him a ball to run in.

Answer
Hi Maja,

Thank you for rescuing the little guy!  It sounds like he bounced back pretty well.

For bedding, consider using shredded aspen.  You can buy a bag of it at pet shops, feed stores, and even some general stores if they have a pet section.  It's extremely inexpensive and very safe, plus much, much better at handling messes than toilet paper (which tends to become saturated quickly and then get very cold).

For food, if he is eating seeds, he can likely stop drinking milk.  The ideal would be hanging a water bottle (don't forget to check Craigslist for affordable second-hand cages, bottles, and supplies), but if that is impossible, provide a daily moist food source which is removed and replaced every 12-24 hours (good options include stale bread soaked in water, a little bit of plain oatmeal, or fruit, for example).  The bulk of his diet NEEDS to be a commercial mouse food.  One mouse won't eat much, so you'll only need one bag, but it will cost you somewhere between $5 and $15.  There is no getting around it - it's what he should be eating to be strong when you release him.  Try to find something pellet based (it can have seeds, but it should not BE seeds), or block based.

He doesn't need toys, just a good hide and some things from around the house to play in.  Good examples include toilet paper boxes with the plastic removed, toilet paper tubes or paper towel tubes, tp tubes with crinkly paper stuffed inside and maybe a hidden treat, or even popsicle and hot glue constructs of your own design.  It's also important that his enclosure be secure.  Anywhere that his head can fit, the rest of him can fit.  This becomes even more important as you add levels and toys that he can climb and use to hop out and escape.  Another thing to consider is ventilation - If you use a plastic bin, you need to either have one tall enough he cannot climb anything to get out and leave it open, or employ some kind of mesh lid and maybe mesh "windows."  Otherwise the cage could get pretty stuffy and stinky pretty fast.  Honestly, a second hand cage specifically for mice or a 10 gallon tank with a locking mesh lid are probably your easiest bets.

You don't need to do anything special to prepare him for the wild.  His instincts will be in tact, in fact, it takes several generations of domestication to lose them.  Once the weather is warm enough that he won't sink into the snow, just release him very far away from buildings into a covered area safe from flying predators, and he'll figure the rest out on his own!

If you have any other questions, just let me know.  Best of luck!
-Tam