Two Male Mice

Question
QUESTION: I have two three month old male mice who are brothers.  One is more aggressive and sometimes picks on the submissive one.  The submissive one becomes scared when the aggressive one picks on him.  I have separated them before due to this and they have been fine when put back together.  Last night I put a plexi-glass divider in the tank to separate them.  I attempted to put them back together three times this morning but they were fighting so are now separate again.  The aggressive one now is distressed and the submissive one is fine.  Did I make the right decision in separating them?  Can they ever be reunited again?  Why did they fight upon being reunited this morning?  I now feel very bad and wonder if I've ruined their quality of life.  They had always slept together and the aggressive one groomed the submissive one.  Thank you for your help.

ANSWER: Don't worry you did the right thing! They may have fought to the death or injured each other seriously.

A mischief of mice always have a rank. You will have a dominant mouse who gets the best pick of food, females etc. He stays top mouse by mating and fighting the others in the group. If he feels threatened by the others he may fight to the death to keep his authority. This behaviour is present more so in males then females.

The larger the cage the less likely they are to fight as they each have their own territory. Include lots of hiding places in the cage such as tubes, huts, hay etc. This gives your submissive one chance rest. Depending on the size of the cage, you will need to clean them out fortnightly. Changing the environment too much may encourage fighting as mice like to mark their scent on their territory. Mice will need to re-mark their territory every time the cage is cleaned and this will result in fighting.

You will have to be the judge on whether or not to introduce them again. Moderate squeaking and the occasional bite isn't a serious problem. If the submissive boy looks stressed or isn't eating or drinking then it is best to keep them apart. Mice are social creatures and thrive when kept in groups. Even lots of human attention isn't enough to keep a solitary mouse company.

Castration is an option, it will reduce any aggressive behaviour and they generally live longer. I have castrated mice and this is usually what happens. Look for a vet who is experienced in this area.

Please feel free to ask any more questions. Good luck!



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

QUESTION: Thank you so much for your answer!  I appreciate your help!  I have another question - Do you know why male mice fight upon being reunited?  I am trying to learn more about male mice as I've never had them before.  I've had hamsters, gerbils and guinea pigs.  Thank you again!

Answer
They fight because they have to assert the pack order again. However it's OK to separate them during play time, just make sure you get your 'human smell' on both mice so neither smell different. You could also try plain boiled rice as food, that way they won't fight over the best bits!

Please feel free to ask any more questions. Good luck!