feisty mice

by ava001 Tue 14 Jul 2020, 10:08 pm

Hello! I currently have two female mice who squeak loudly and chase each other around their cage often. I have had them for about a month and they sleep together in their nests every night. The girlies live in a 40-gallon tank and I've read that they might be getting territorial because the enclosure is too large. For most animals, a bigger enclosure is better but is this simply not true for mice? I have also read that group dynamics are better in groups of 3 or more. For a 40 gallon, how many mice should/can I house comfortably? I took a look at the cage calculator and 9 critters sound incredibly overwhelming! Would adding more females fix my issue? I just want to make sure that adding more mice will fix the problem and not overcrowd the tank. Thanks!

by chiroptera Tue 14 Jul 2020, 11:46 pm

If they're just squeaking and chasing, and there's never any blood being drawn, and both are able to eat and drink, it's not a huge issue! However, it is true that trios sometimes do better than pairs, since in pairs, if one mouse is bullying the other, there's no respite, but with more, the aggressor won't be able to always pick on one specific mouse, and the more submissive mouse will still be able to have some company.

I personally have found that 6 mice is a good amount for a colony. Depending on the mice, they may still accept more than that, but it's usually what seems to work the best for me? Or rather, up to 6, not exactly 6.

If nine mice is too many for you to handle, definitely don't get that many - though it might not be a bad idea to introduce a third, if you're able to!

As for having too big of a cage, I don't think that's the issue. Sometimes, if you have two connecting enclosures (ie. connected via tubes), that will make a bigger colony split and become territorial, but I don't think a single 40g tank would make two mice fight in that way. Plus, they're both sleeping in the same space, which means they aren't staking out separate territories within the enclosure, which is what might back up the argument that an enclosure is "too big."

I think that your mice, and a few more if you choose to introduce some others, will enjoy all that space! Chasing and squabbling is to be expected at times, and I don't think it's reason to downsize them or to separate them, unless they're drawing blood or show other signs of stress or malnourishment due to the squabbling.

However, if you do decide to introduce some new mice, some people do recommend doing the introduction and taming in a smaller tank - I don't, personally, and have rarely had issues with my female mice getting along, but others say it's easier to do so in a smaller tank, and then move them over to the permanent enclosure, so it may be something to consider.