I have to agree that the enclosure is too small for mice to honestly be stimulated enough. I understand not waning to use up a ton of space for breeders, but a certain amount is necessary. I realize they're in something bigger now, though it still seems crowded to me.
Mice are high energy animals and while it can be hard to determine how much stress they're honestly experiencing because of space constraints it stands to reason that they need a bigger space than what you had them in.
I'm curious, when you raised them in a shoebox sized container did you observe them enough to be able to fairly judge their behavior? Because I've seen mice (2-5 per container) raised in shoebox sized containers virtually their whole life and they do show signs of stress and what I can only assume is insanity.
I've seen them fight, not always drawing blood but fighting is fighting. Chunks taken out of ears where common, as well as infected bites to the face.
Circling was another problems. Just running in a circle, kind of like chasing their tails. But just going and going and going.
Obsessive chewing was another problem, but that's hard to tell if that was because of a lack of any type of chew or not.
And of course, cannibalism. Of babies and adults. Though to be fair with pinkies it could have just been an overly disturbed or bad mother mouse.
I think a wheel would be appreciated, even if you don't witness them use it during the day time and if one buries it doesn't mean
other mice don't want to use it. Hamsters have been known to run 8 miles in a single night on a wheel! I imagine mice are similar. Maybe a different kind of wheel would be better, too.
They are so goshdarn adorable. I've been considering getting mice lately.