The Harvest Mouse
Keeping Harvest Mice as Pets
1 Discovery and Context
2 Micromys - Description
3 That Wonderful Procreant Cradle
4 Where Are They Now?
5 Deaths and Entrances
6 Keeping Harvest Mice as Pets
Harvest Mice are easy to keep in a healthy condition and make interesting but not touchy-feely pets. They grow accustomed to having people present and active around them and behave as normally as their conditions allow.
They can be kept in a home-made cage built from plywood, glass and mesh where the size can be made sufficient for valuable studies of a small population. More commonly they are housed in aquaria or terraria (though there is no need for the supplementary heat). Suitable tanks can be found that have a decent vertical component and these are well suited to the purpose because of course, Harvest Mice like to climb. You will nee to improvise a mesh lid. The mesh needs to be quarter inch - if you use half inch mesh, the mice will walk staight through it! You can cut the mesh one inch bigger all round then fold it over but it is likely to warp and cease to be effective. It's better, and more attractive to make a perimeter with some wood and attach the mesh with tacks. It doesn't need to be a tight fit as the weight will hold it in place.
I have kept Harvest Mice for several years and I line the tank with a generous depth of wood shavings (saw dust is not suitable) topped off with a big handful of nice-smelling hay. I feed them from a small pet bowl and provide water from a small-mammal drip feeder. The tank can be “decorated” with anything that they can climb around on. I find old ivy sprigs ideal as it is woody and much forked. A millet head dangled from the top (I hold it in place with a clothes peg) provides extra food and climbing facilities and there is little else they need. You can add "toys" like artificial finch nests and those balls of woven willow but I avoid plastic or brightly coloured materials as the tanks look nicest when they appear as natural as possible (in my opinion).
Foodwise, I provide as much diversity in the form of seeds as I can find. Good quality wild bird food mixed with a canary feed works well but I also add sunflower seeds (if these aren’t in the wild bird mix), dried mealworms and a few flakes of fish food for extra protein.
They love to have something new to investigate so in summer mine get a cutting of bramble, seeding grass head, or hogweed head when they are available, though they survive perfectly well without these.
Their urine is unnoticeable and their faeces are tiny and dry. They don’t smell of acetamide as “fancy” mice do but after a while the tank does develop a mildly unpleasant aroma and although the mice don’t like the disturbance, they need to be cleaned out now and again - perhaps every three months. The safest way of handling them is to tempt them into a clear plastic tube (such as those supplied for tennis balls or “Avia” canary seed). They often wander in quite readily and they can then be kept somewhere else temporarily whilst their home has a spring clean. If they are determined not to be caught they can be picked up by the tail quite safely but be prepared for them to turn up and nip your fingers – they can fetch a drop of blood.
If one escapes and is darting around on the carpet a careful approach with a clear plastic tube will again be the safest way of recapturing it. If one finds the back of the kitchen cabinets to its liking and is reluctant to show itself, put some food and water down for when it does come out and bait up a humane mouse trap. This works very quickly for me normally.
A pair of mice can be bought quite cheaply from private breeders and some pet shops sell them but think carefully before you venture into keeping Harvest Mice as pets. It would be cruel to leave them for more than twenty four hours at a time, as the water can get clogged or drain away or other unforeseeable events could occur.
Unless you want a lot of trouble, I recommend you procure a couple of males as these will usually get on well together and will not produce babies. If you really want to witness breeding, you will need more than one tank - three at least, and be prepared to handle and move the mice around at set ages.
I was interested in learning more about Harvest Mice so I set out with a pair in the first place and my young pair began breeding as soon as they were sexually mature and this probably happens normally. I was assured they came from different lineages. If you have several mice of different sexes in a tank, only one pair will breed. This will be the dominant pair. If you want the others to breed, you will need to remove them to another tank and the subsidiary dominants will then pair up. If you want to rear more than one litter from the same pair, you need to leave the male in the tank throughout. If you remove him and introduce a new male, they will not breed. When the female is attending her babies she will bully the male mercilessly and he will often be seen looking very miserable at the far distant corner of the tank, but he will come to no harm.
When the babies are first out of the nest, I ensure they get water by providing it in a shallow dish - very shallow to avoid any drownings - as they may not be able to reach the water dispenser. When they are independent, at about 20 days old, they should be removed as the female will become intolerant of them if she is ready to produce another litter - she may have been mated immediately after giving birth and be heavily pregnant by this time. There is no need to separate the sexes yet but this will need to be done before they are six weeks old - or things will begin to get truly difficult! More seriously, if you permit siblings to breed with each other you will be risking genetic problems developing.
Once again, the clear plastic tube will come in handy as the contained mouse can be inspected from beneath without any handling (which will be unlikely to prove effective anyway). Some people do it by watching the mouse as it clambers around on the underside of the mesh lid but how they then keep track of it and remove it is a mystery to me.
Males have a swelling - a definite lump near their anus and if the penis is visible it is in their tummy region - quite a way from the anus. Nipples may be visible on the females but they are quite well furred below, and there will be no swelling near the anus. If you get this wrong you will know in about three weeks time!
Adoption or Release?
So what are you going to do with all these mice? If you have sexed them correctly and separated them accordingly, you can put a halt to any more coming along but you will probably find you already have more than you really want to maintain. You may find a local pet shop will take them (but I know of someone who found the pet shop ceased trading unexpectedly) or you can release them into the wild.
I doubt if they have any lesser chance of survival when introduced into the wild from captivity than if they were expected to make their own way from being recent nestlings, and I don't see it as cruel providing some measures are taken to maximise their chances. First and foremost the habitat of the release site needs to be suitable. If you haven't found their nests in the wild you might not be able to assess this and then perhaps someone with this knowlege will be traceable via the local Wildlife Trust. Apart from this, I choose a period of settled weather and cast a generous spread of whatever seed mix they've been accustomed to. As they venture out of the release tank, they will quickly disappear - never to be seen again. It is probably illegal to release captive bred Harvest Mice into the wild without a licence even though they are a native species.
I do not believe there is any need or justification in captive breeding programmes to supplement or maintain wild populations. If there is suitable habitat within their natural range, then Harvest Mice will thrive. There will be population fluctuations but if Harvest Mice are definitely not present then introducing them will not achieve any long-term benefits. Better habitat management combined with wildlife friendly corridors for their distribution, so that they can readily re-colonise suitable places, would be a better conservation aim.