The most common type of mouse available as a pet is the domestic pet mouse. These pet mice have been selectively bred to enhance the desirable qualities of the mice. There are also spiny mice (which are desert creatures that are a bit trickier to care for), but for our purposes, we will discuss the ordinary domestic mouse.
Ordinary does not mean boring, however. If you have ever seen a group of pet mice playing, you realize they can be quite entertaining pets.
They are a bit skittish and harder to handle than some of the larger rodents such as rats, but they can become quite tame and will take food from the hand and allow themselves to be handled if started at a young age. Mice are quite ideal as small pets that are entertaining to watch, are easy to care for and make very few demands on their owners.
Their short lifespan is one of the biggest drawbacks of mice. On average they live for about 1.5-2 years, although they can sometimes live up to 3 years.
Mice are nocturnal and very social. They will be very active in the evening and night, but don't expect to do much with them during the day. Being social, they are best kept in groups. A pair of females is the easiest, although larger groups are fine if you provide the cage space. Pairs of males should be avoided, unless they are litter mates, never separated, and given a large enough cage that they can have their own space (unfamiliar males are very likely to fight).
Keeping males and females together should be avoided unless you want lots of mice in a short amount of time.
Choosing Healthy Mice
When picking out your mice, look for active bright mice, with smooth clean coats and pink clean skin on the ears and tail. The eyes and nose should be free of discharge, and the mouth and anal areas should be clean and dry.
Their breathing will be relatively fast, but should not be labored or noisy. Check the cage as well - it should be clean (the mice have been well cared for) and the droppings should be formed.
Look for a pet store that separates males and females at a young age (good breeders will do this). Mice can reproduce by about 6-8 weeks of age, although this is very stressful on the female and should be avoided. If your pet store doesn't separate mice at a young age you may well end up taking home a pregnant female. To tell the difference between young males and females, check under their tails for the distance between the anal opening and genital opening - this distance is shorter in the females. A breeder or pet store should be able to do this for you, but it can be hard to do in young mice unless you have males and females to compare to each other. In older (6-8 week old) male mice, the testicles are usually readily visible.
The size of the cage you will need depends on how many mice you will keep together.
For a pair or small group of females, a 2-foot square cage is ample space. Mice will appreciate a cage with multiple levels as they do like to climb, and it should be fairly tall.
Type of Cage
Glass aquariums and wire cages are the best types of cage for mice. Aquariums will need a tight fitting mesh lid and lots of furnishing supplied for climbing and playing. It is also important to remember that ammonia and other fumes will build up faster in an aquarium or plastic sided cage than in a wire cage. However, as long as the lid is tight fitting, they are pretty much escape-proof and have the added advantage of allowing a deep layer of bedding that the mice cannot spread all over your floor.
Wire cages (with horizontal bars) are nice because they provide lots of climbing opportunity on the sides of the cage, and it is easier to fix furnishings, platforms, and toys to the sides of the cage. The most important thing is to make sure the bars are not too narrowly spaced so that the mice can escape (or get stuck trying to escape) and that the doors are placed to allow easy access to the entire cage for when you need to catch the mice. Wire cages marketed for mice are generally quite small, so larger hamster cages or even bird cages are preferable, but ideally the bar spacing should be 1/4 inch. Do not underestimate how small of a space a mouse can squeeze through (one of my girls, Phoebe, could quite easily break out of a cage with 1/2 inch spaced bars). Avoid using cages with wire mesh floors - solid flooring is a lot easier on the mice's feet.
The modular plastic cages meant for hamsters are actually well suited to the mouse size and activity level but are difficult to clean, are sometimes poorly ventilated, and a determined mouse could chew right through the plastic.
Placement of the Cage
The cage should be placed where the mice will have lots of human contact to make taming easier. It should be out of drafts, away from direct sunlight and out of reach of other household pets.
A deep layer of aspen shavings or some other suitable substrate should be provided in the cage. Avoid cedar and pine shavings due to the strong volatile oils released from these woods (especially cedar). Aspen or other hardwood shavings appear to be a better choice. Another alternative is paper or wood based cat litter - it is very absorbent and good at controlling odors. It is more expensive, but you will likely use less. See "Top Ten Alternatives to Cedar and Pine Shavings" for more ideas.
In addition, nesting material should be provided. Strips of facial tissue or soft paper towel will happily be shredded by mice and make nice nesting material. I don't usually recommend the commercial cotton bedding material you can buy because some has strands that can get caught on the mice's feet. Hay can also be used.
A nest box should be provided and can be store bought or homemade. Small cardboard boxes are fine, although they will be shredded over time and need to be replaced fairly frequently. Clay flower pots, either with holes cut in them or placed on their sides can also be used, as can PVC plumbing pieces you can find at the hardware store. The nest material should be cleaned out only every month or two as needed (more frequent changes may be too disruptive).
Mice need lots of opportunities to play and exercise. Mice seem to universally love running on wheels so try to provide one if at all possible. A solid surface wheel is easier on their feet than wire wheels. Also provide some tunnels or tubes (plastic plumbing pipes sections or paper towel or toilet paper tubes). For other toys, wood blocks and houses, small cardboard boxes, ladders, cotton ropes, egg cartons (paper only), small willow balls, and anything with holes to climb in and out of will happily be used as playthings. Use your imagination and provide lots of variety, just make sure they are not ingesting bits of plastic or other parts.
For water, a gravity fed water bottle with a dispenser is preferred as it can't tip and keeps the water clean. A shallow food bowl of ceramic or porcelain is the best choice as they are difficult to tip, won't get chewed up and they are easy to clean.
Depending on the size of cage, it may need to be cleaned quite frequently, especially glass or plastic sided cages that allow ammonia and odors to build up more quickly. It is best not to wait until you can smell a problem because it will be quite overwhelming to the mice by then. However, the mice do need to mark their territory and if their cage is completely disinfected too frequently they may be distressed. A good compromise is to leave a bit of the old shavings or litter in the cage at each cleaning (so their scent remains), and only do a thorough scrubbing and disinfecting when absolutely necessary.
Mice can be fed a commercially prepared complete diet - a rodent mix or hamster diet is acceptable. Pellets are available for mice and are completely balanced, but this is a monotonous diet. Grain and seed-based loose mixes provide more interest to the mice and will probably be more readily eaten. However, your mice may just pick out their favorite bits and leave the rest, leading to an imbalanced diet. I prefer to feed a combination of balanced pellets and a mixed diet, but only offer small amounts of the loose mixed diet at a time and make sure it is almost all eaten before offering more.
The basic diet can be supplemented with small quantities of fresh fruits and vegetable (greens, apple, carrot, etc.). Watch for diarrhea, though, and if a particular food item does cause diarrhea, discontinue feeding it. Sunflower seeds are a favorite treat of many mice (but are quite fatty so should be limited), as well as other seeds like millet spray. Cooked pasta and whole grain bread or crackers can also be given, maybe with a tiny amount of peanut butter as a special treat. Commercial treat sticks make a good treat but only very occasionally as they are often quite sweet. Avoid feeding junk foods such as candy and potato chips, and never feed chocolate as it is toxic to mice and other small pets.
Most mice will become quite tame given time, patience, and perhaps a little bribery. At first, allow the mice time to become accustomed to their new environment. Once the mice are calm, start spending more time around their cage and quietly talk to the mice to get them used to your voice. As the mice become comfortable or curious with your presence, start offering some favorite tidbits (try millet or sunflower seeds) by hand, and once the mice are taking treats from your hands, they may start walking on your hands, or you can start trying to pick them up.
When picking up a mouse, it is best to try scooping it up by cupping your hand under the mouse (but do not squeeze or tightly grasp the mouse's body). If holding a skittish mouse, you can try holding the base of the tail with one hand while supporting the mouse's body in the palm of your other hand to prevent the mouse from jumping off your hand and possibly injuring itself. Similarly, you can hold a mouse by the base of the tail and gently lift a bit to allow you to place your hand under the body to pick the mouse up. It is vital that you only grasp the base of the tail gently and very close to the body. If you hold further down toward the tip of the tail, you may break the tail off or the skin may come off the tail.
Be careful when holding mice as a relatively short fall can cause injuries. It is best to hold the mouse just above your lap or some other soft surface in case it falls or jumps.
If you need to pick up a mouse that isn't yet tame, place a cup (or paper tube covered on one end) on its side in front of the mouse, and gently herd the mouse into the cup, which can be used to carry the mouse. It is also possible to pick up a mouse by the very base of the tail if you have no other choice. This doesn't really hurt the mouse, but it is stressful for them and probably uncomfortable.
If you are going to allow your mouse time outside the cage, you will need to mouse-proof the room. Ideally, keeping them contained in a large shallow plastic storage box, small wading pool or some other confined space is the best option for keeping the mice safe and sound. Even then, you should make sure there is nothing that your mouse can get into and hide (such as the underside of the couch, or very narrow space between furniture), or any way that the mouse can escape on you. Make sure all electrical cords are out of reach, and that there is nothing else that could harm the mouse including poisonous plants. Remember, mice can be pretty hard to catch so make sure they don't get away on you!