male mice from the same litter fighting

Question
Hello..
My children have 11 mice. It all started when they saved two mice from being eaten by a snake. Now they have babies. Right before the female had the babies we separated  the father from the mother. After the babies were born we separated the male babies from the female babies, once they were old enough to be weaned from the mother. There was only one female baby so we kept her with her mother. As for the males (there a 8 of them), we keep them in a separate cage. They seemed to be getting along just fine, but recently they have been fighting. We inspected each one and they seem to only have bite marks on their tales. We are concerned. We are not sure why they are fighting, or what we should do about it. Any information you can give us would be much appreciated.

Thank you,
Alexis, Haley, and Ian

Answer
Hi Alexis,

I wish I could say this didn't happen often, but it's a pretty common problem.  Once males sexually mature they can quickly turn aggressive.  Once you see the injuries start is the best time to separate them from each other, as you might not be able to predict when it becomes more serious than just tail-biting.

They fight because mature male mice are extremely territorial.  In the wild males have little if any contact with each other, and will mark their territories by scenting pretty much everything.  I have tried spreading them out across larger cages, but in my experience, once it starts it only gets worse.  It might be possible to calm them down for a little while by dabbing a very small amount of real vanilla under their chins and at the base of their tails, but this is not a permanent solution and shouldn't be done all the time.  I would watch them closely - is there only one mouse causing a problem and biting tails?  Is it all of them?  If you can find a trouble maker you might be able to fix things just by pulling him out.  If it's all of them, the most responsible thing to do would be to separate them all.  This isn't an optimum solution, but it's better than finding one or more dead.  :(  Would it be possible that a local pet store or rescue could help you find good, snake-free homes for some of them?

I'm sorry I don't have better advice to give.  My fingers are crossed that it's just one doing the tail-nipping!  Best of luck!

-Tam