I added a new mouse recently to my colony of six. My colony was previously two sets of three that came together and were introduced after the quarantine period. Everything went very smoothly and they all took to each other like they'd known each other their whole lives.
The new mouse is a lone female--her two littermates were each adopted individually and I felt bad seeing her alone and brought her home. I know mice shouldn't be alone so she was stressed, and when I finally went to introduce her to my other mice everything went great. She was a little jumpy at first but after about an hour they were all in a cuddle puddle. They've since been moved into an enclosure (a small one that is not the main enclosure) temporarily while they bond. But I've been hearing a lot of squeaking and she jumps around a lot--it seems like one of my mice in particular is going after her but I don't know why. Is it just hierarchy stuff or bullying? How can I tell?