Q: I just got a new mouse to put with my other mouse. The first mouse is named Da Kurlzz and is a full-grown male. The second mouse is a young male. (I don’t know how young, but he has hair and is half the size of Da Kurlzz). Da Kurlzz is very territorial. He tries to bite me when I put my hand in his cage, but when he is out of his cage he is very laid-back. When I first put the mice together, Da Kurlzz bit the smaller one, he jumped at him and attacked him. When I take them out of the cage they are fine with each other but, like I said, Da Kurlzz is very territorial. What do I do about Da Kurlzz’s territorialness? How can I put them together without them hurting each other?
A: Your mice should be separated immediately and they must stay that way. Male mice are extremely territorial and will often fight to the point of death. Occasionally young brothers will tolerate each other well until they are around 3 months old, but I separate them at the very first sign of any type of aggression.
Da Kurlzz is being a completely normal male. His cage is his territory and the introduction of the new male has made him even more protective of it. Once he is secure with his territory again, you may see a decrease in his attempts to bite you.
I have heard of people who have male mice that lived together, but it is very rare. I never recommend that people try it; it is simply too risky.
It may seem sad at first to keep your mice alone, but they truly are happier and safer this way. Make sure each mouse has lots of toys and hiding spaces in its cage, and you will find that they will be quite content.