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Mice/introducing new mouse to group, dealing with stress?



So I recently bought a fourth mouse to introduce into my original three, with the hopes that they might make a good friend for the littlest one who gets a bit bullied (nothing serious, but she gets chased around sometimes and likes to sleep by herself in a different part of the cage). I figured a slightly younger mouse might make a good match, since the bigger two would probably just assert themselves, but i seem to have underestimated the younger mouse's force of personality.

I did the thing where you trade the mice between each other's cages to get them used to each others' smells before the first introduction on neutral turf, and it seems to have half-worked? The smallest mouse seems to get along okay with the youngest, which is good, that was the plan. The biggest one, not surprisingly, got territorial and always goes in for a fight. (No blood has been drawn because I always separate as soon as things get squeaky, but if you have any advice for when I should intervene on these interactions that'd be cool too. If they're just grappled to each other and no one is squeaking, do i separate? How can I tell when things are actually getting nasty and I shouldn't try again).

My main conflict, though, is that the other large mouse actually ended up being submissive to the young mouse, and it seems to have stressed her out A LOT. She's always been skittish, and over the months she's come to trust me more and come out of her shell, but after the interaction with the young mouse she was running around more than usual, nipping at my hands, and stress-peed on me. I separated them again and she seems to have recovered slightly over the past day, but I worry that if I try to keep them together permanently, she'll just end up being a little fuzzball of stress 24/7.

Do you know if, over time, she would get used to the new mouse and be less stressed? Is the new mouse being more dominant actually a bad sign for possible friendship for littlest mouse? It's really hard to get a gauge on personality when new mouse is by herself, but also it's hard when they're all stressed with each other. I have until the end of Thursday to really decide if I want to keep her, and I'd rather return her to the store than have her by herself forever (even if it breaks my heart).

thanks a bunch!

ANSWER: Hi Ashley,

A little tussling is okay, but there are some clues to watch for that indicate "real" fighting and should be stopped before someone is hurt.  They include:

- Biting or scratching (blow backwards on the fur to check for new scabs, or feel for bumps)
- Tail rattling (buzzing the tail really, really fast against a hard surface)
- Boxing (standing up on the back legs and "punching" outward at the other mouse with the paws)
- Any injury which results in bleeding or scabbing

It always takes mice a few days to really settle into the new pecking order, but as long as you don't see the above signals and everyone can get safely to food and water, it should settle down.  You can also try dabbing a teeny, tiny bit of vanilla extract (REAL vanilla extract only, not imitation) on the base of each mouse's tail and above each nose (if you can).  This sort of resets everybody - everyone smells alike until it is cleaned away, and it really sticks in their noses for a while.

It sounds like you are doing well so far, but feel free to observe right up until Thursday as long as no one is getting hurt.  The longer you can safely leave them together without separating, the sooner they will learn the new order of meeces.  If, by Thursday, you still haven't been able to trust them all together, and you don't want to consider splitting them into two (the biggest two) and two (the small two), then you can always return her (or find her a new home).

Hopefully this helps, but if I missed something or you have more questions, please feel free to write me back!  Best of luck!


---------- FOLLOW-UP ----------

QUESTION: Thanks for the response!

So do you think the skittish one will be able to get comfortable again after they've re-ordered themselves? I just worry about her tiny fuzzy stress levels and I wanna make sure I'm most likely not gonna make it really suck for her if I keep the new mouse.

As far as other questions with introducing them, I do have a few specific:

1) Is it better to introduce one-on-one (what i've been doing), gradually introduce one mouse into neutral territory at a time, or all of them at once?
2) How long at a time should I keep them together for while introducing? I usually keep it pretty short, just so I can make sure I can intervene quickly if I need to, but I have had new mouse together with smallest mouse for almost an hour before smallest mouse got bored and wanted back into the main cage.
3) How long can I keep them apart without essentially restarting the entire introduction process? I keep the new mouse in her own tank right now so that there isn't the risk of fighting while I'm asleep or at work, and this is a concern I have.

I appreciate the help so much!! I love my babies and just want to make sure I'm doing the best job I can


(p.s. Do you know what the mouse is trying to communicate when she rattles her tail at YOU? I've always assumed some kind of indignance, but I can never get a consistent answer out of the internet.)

MOST of the time, yes, they will be able to all relax once the new order of dominance has been established.  You don't really need to go as slowly as you've been going - there's not a better or worse way, but like ripping off a bandaid, it might be nice for them to figure each other out all at the same time (if it can be done safely, that is).  Then they are only getting used to one new situation, instead of multiple ones when this new mouse sometimes appears and sometimes doesn't, and everyone scrambles to reorganize themselves.

Once they've been introduced once, you don't need to do it again, so to answer your question #2, however long you feel holds their interest and doesn't end poorly.  You can exchange dirty bedding between their cages, too, so they can continue to sense the newest mouse around even when she isn't.

Every time you remove the new mouse, you restart to some extent.  If you put the cage by your bed, you'll know if they fight, because the squeaking will wake you up.  Not too pleasant of a way to wake up, but effective!  If they get through the whole evening and overnight without violence or signs of impending aggression, it's unlikely they'll fight while you are at work, when mice usually prefer to sleep.

When a mouse rattles their tail toward you, creating a buzzing sound, they are sending the same message they send to offending mice: "Back off, I'm feeling cornered and I will bite if I feel I have to."  It's usually a frightened, anxious reaction that might happen as a result of approaching too fast or from above.

I think I got all your questions, but it's been a weird week, so if I missed something please let me know!



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