Mouse Husbandry -- Things to consider

by River Sat 23 Jan 2021, 2:33 am

The debate over the minimum cage size for mice has been going on for years, and unfortunately, there never seems to be any rhyme or reason to the new minimums chosen. Every forum you join says something different, which leaves many owners (regardless of experience level) feeling very overwhelmed.

I don't want to add to the confusion, and won't be recommending a minimum size in this post. Instead, I'll try to offer as much information as possible so you can make an informed decision on how to care for your mice. This may be a little clunky!

HOW BIG IS A WILD HOUSE MOUSE'S TERRITORY?

It depends! The house mouse is an animal built to adapt, and their behavior will change to suit the environment. House mice who live in close proximity to humans often have an excess amount of food available to them, resulting in densely populated, small territories. In these populations, their territory is often just a few square yards and can be even smaller. Some sources claim they travel anywhere from 5-30 feet from the nest.
In non-commensal populations, who have less access to food and water, territories are large and defended much more aggressively. Exactly how large these territories are is highly variable, according to this study. At the smallest, it was roughly 0.0002 hectares or 3,100 square inches. Males may be more active.

DO OTHER COUNTRIES HAVE DIFFERENT MINIMUM RECOMMENDATIONS?

Absolutely. In Germany, Austria, and some other European countries, the current recommended cage size for a group of four is roughly 39x20x20 inches (780 sq inches of floor space) or 100x50x50 centimeters. They also recommend the enclosure has at least one level. The language barrier has unfortunately prevented much of this information from being shared, and while I speak a small amount of German, I could not find out how this minimum was decided.
In comparison, the most common recommended cage size in the US is 360 square inches for three mice. The standard in the UK is often only very slightly larger, and in both regions, it's highly debated.
To get an idea of what these minimums look like, here's a comparison. This photo isn't mine but was shared here many years ago. If the owner would like me to remove this, I gladly will!
Pictured is an eight inch wheel, a bendy bridge, a toilet paper tube, a food dish (diameter 3.5 in) and an 11.5 inch wheel. We can see a 10gal (200sq in), a 20gal (360sq in), a 40gal (648sq in), ~775sq in, and ~1,550 sq in.

Mouse Husbandry -- Things to consider Tumblr_p48nnjM2sa1x3jl7oo1_500

HAVE THERE BEEN ANY STUDIES ON MOUSE CAGE SIZE?

Yes, although not many.
This article studies enrichment, which includes cage size. More space and more toys showed an undeniably positive effect on the mouse, potentially even suppressing the growth of cancer.
This study is similar to the above one. Again, the mice with the most space and enrichment performed best and were less anxious.
This study, done with males, is a bit more of a gruesome read. Many male mice were housed together and fought more frequently when they were given more space to roam. It otherwise had no impact on their behavior. To me, this is further proof that males shouldn't be housed together. Even if they get along, they would have to be deprived of a large enclosure.
Please link any other studies you find on the topic. Smile

WILL A LARGE CAGE CAUSE STRESS AND ANXIETY?

No, there's no evidence to support this claim. In fact, the above articles suggest it's been disproven! This belief seems to be more commonly held by breeders. Some will give anecdotal 'evidence' to explain why they believe this, but their reason is almost always a sign of poor breeding and not a sign that the cage is too large.
Mice are a prey species, though. They won't feel secure in an open space so no matter the cage size, you should do your best to clutter it. They should always have somewhere nearby to run and hide. If not, yes, they'll be anxious!

HOW DO I KNOW IF MY ENCLOSURE NEEDS A CHANGE?

Some forums (including this one, for the most part) have decided that there isn't enough information available to recommend a true minimum. Instead, they encourage individuality, where you adjust according to the specific colonies' behavior. Signs of poor welfare in mice, as cited in certain scientific studies, include:

Unkempt fur
Lack of activity
Bar chewing and other stereotypies (barbering, scratching, pacing, jumping, etc.)
Excessively dirty nest or lack of nest
Irregular sleeping pattern
Regularly sleeping in the open
Aggressive or overly fearful behavior
Low or high body weight not related to genes (excessive eating or under eating)

If your mice are showing the above signs, then it's time to evaluate their cage size, enrichment items, and overall health. However, this can leave a little too much room for error. It's smart to go as large as you can right from the start, and then adjust accordingly.

I hope this information helped someone come to a conclusion. These are all the things I thought about when upgrading my mouse enclosure, and my views changed a lot during the research process. Please feel free to add on where you feel fit.

by River Sat 23 Jan 2021, 2:37 am

I wrote all of this at 2 AM so if anyone feels it needs a rewrite, feel free! Laughing

by Oreoandfriends Sat 23 Jan 2021, 10:12 pm

Great information!! I LOVE how you based it off of studies, it makes it a lot more useful than other baseless cage size suggestions.
I know cage size has always been debated, but I think it’s important for people to aim for as big of a cage as they can and upgrade if their mice need it. Some mice are happy in a 20 gallon aquarium, others are stressed unless they’re in 1,000+ square inches.
In my opinion minimum cage size recommendations are good for preventing potentially neglectful situations, but I definitely think that small animal owners need to realize the difference between minimum and ideal.
I envy German cages and I’m hoping to DIY one of that style in the future, I really wish the US had large commercial cages available though.

by River Sun 24 Jan 2021, 1:04 am

Their behavior is so highly variable, even in the wild! It's really incredible. I hope to take on a DIY project eventually as well. Having just one mouse (for now!) has let me really hone in on what his specific needs are. Mr. Bald absolutely adores exploring and climbing. He knows no fear, so I think he'd adore an extended topper. I've taken some inspiration from German designs since they're very common over there. It's been a great opportunity to work on learning a new language as well.

Fun fact: the noun 'mouse' is feminine in German, meaning you'd say 'meine/eine/die maus' rather than 'mein/ein/der maus' regardless on if the mouse is male or female. This tripped me up for a while. The languages are similar, but German has so many more opportunities for mistakes. Laughing

by SarahAdams Sun 24 Jan 2021, 12:23 pm

You might enjoy seeing Erin's triple-level enclosure and expanded environment, all for one male mouse. Smile

https://www.youtube.com/watch?v=fgN5CsGO7Og&list=RDCMUCFmrfBN7qjyP5j8nbw6sO1w&index=3

by AngelaJ Sun 24 Jan 2021, 8:02 pm

Fabulous, thanks for sharing

by Dee67 Mon 25 Jan 2021, 4:38 am

Thank you @River for taking the time to put down that information for us all. Appreciate you!

by EverythingAnimal Tue 26 Jan 2021, 2:25 am

I'd like to see a study where they increased either the amount of space or number of toys not both. Then we could see which change really produced most of the positive effect.

For example, yes you can fit more toys in a 20g than a 10g.
But will mice with the same amount and type of toys in either tank, the only difference is size, be significantly happier in the larger tank, or will there be no real change?

Would a very densely packed 10 gallon be more enriching to the mouse than having fewer toys in a larger tank?

The obvious choice is the best of both worlds, but I really do wonder what makes them happier. Is being happier in a larger cage just a side effect of fitting in more toys, or is the space itself what does it? Can you accomplish the same effect in a smaller space if you find creative ways to fit in more stuff?

My main question is of course, do I need to feel bad about keeping my mouse in a 10g if I absolutely pack it with toys Laughing

by River Tue 26 Jan 2021, 6:56 pm

EverythingAnimal wrote:I'd like to see a study where they increased either the amount of space or number of toys not both. Then we could see which change really produced most of the positive effect.

For example, yes you can fit more toys in a 20g than a 10g.
But will mice with the same amount and type of toys in either tank, the only difference is size, be significantly happier in the larger tank, or will there be no real change?

Would a very densely packed 10 gallon be more enriching to the mouse than having fewer toys in a larger tank?

The obvious choice is the best of both worlds, but I really do wonder what makes them happier. Is being happier in a larger cage just a side effect of fitting in more toys, or is the space itself what does it? Can you accomplish the same effect in a smaller space if you find creative ways to fit in more stuff?

My main question is of course, do I need to feel bad about keeping my mouse in a 10g if I absolutely pack it with toys

I'd LOVE to see a study that had multiple cage sizes where the enrichment in relation to floor space was the same, so where each enclosure was appropriately cluttered. Unfortunately, I haven't found that yet. Sad

I think it would give us the most accurate answers, though.

I personally believe enrichment is the most important thing. Enrichment improves the welfare of mice in any enclosure size. When floor space increases, enrichment offered should increase right alongside it. The benefit of a large cage could just be that it increases the amount of enrichment that can realistically be provided, or that room to explore is enrichment on it's own...but either way, enrichment is shown to be extremely important.

As prey animals, a big empty space isn't natural for them. If you've ever seen a wild mouse venture out from hiding, they're tense, jumpy, and vulnerable. If a mouse were to be locked into that big empty area, they'd probably end up in a state of chronic stress. This is where I think enrichment and cage size become linked. If a big cage is well-enriched, they can explore and be sheltered at the same time.

(Which is where I should mention that studies should be viewed critically! Most every study I've read, including those linked, don't offer what I'd deem to be a species-appropriate and space-appropriate amount of clutter. In turn, they fail to take their wild behavior into consideration. This could skew results.)

I know this doesn't really answer your main question, but you brought up some really relevant questions so I thought it was interesting! As for your question, though, mice are highly individual by all accounts and I'm not sure if assigning a one-size-fits-all cage size is something I'd be comfortable doing at this point in time. Smile

by River Tue 26 Jan 2021, 6:57 pm

Sorry if I had any typos there. I'm having a ton of lag for some reason

by Dee67 Thu 28 Jan 2021, 1:22 am

I can say one thing, the deer mice I relocated out of my rather full basement, where they had a great deal of space plus a lot of enrichment, were the fattest, glossiest, happiest mice ever

.
PS they were live trapped and gently placed in the open shed so they could readjust to outside life in relative safety.

by EverythingAnimal Thu 28 Jan 2021, 2:15 am

That reminds me, I have a deer mouse that has been living in one of my birdhouses on and off for the last few years, she's had a couple of litters in there! I actually switch out half of the super dirty bedding in there for her now and then and put in carefresh, she usually just chills while I do it.

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