RE: Mouse Biting

Question
Hi, I have pet mice and one of them is biting. He (I think) was first purchased as a trio and I was told they were three sisters! I had someones kid come over and kill two of the mice by chucking them at the cage the third moue was in and then they put the dead mice back in the cage. The mouse that has been left behind has (understandably) been very traumatised by this event. I cleaned its cage to remove the scent of the other mice and went and purchased two more. However, the mouse will not accept the new ones and has tried to kill them, especially the baby one. We have housed them in different cages and I put them next to each other so they can see each other. The old mouse goes crazy sniffing and climbing etc while the new muse pays little to no attention. When I put them together, the old mouse straight away bites the other mice. One of them is even from the same litter as the original one. I have been paying extra attention to the sad mouse and have not been handling him. At first he used to shake like crazy but he is slowly trusting me again. I am pretty sure he is actually a he, and do not know whether to leave him on his own or keep trying. Any ideas will be appreciated.

Answer
Hi Lisa,

How awful!  I am so sorry to hear how your first trio went.  I would be traumatized, too!

His new behavior may be a result of the incident, or it may simply be that he doesn't want cage mates.  Mice that will normally not get along with others frequently make an exception for siblings, since they grew up around each other.  Once separated, however, they may change their mind!  Males also typically prefer to live alone unless breeding, and even then some may show too much aggression.  Regardless of the cause, it seems he is being stressed by the presence of the new mice, and biting is kind of a signal that pairing them is just not going to work out right now.  It may be a good idea to move the cage of new mice to a different area of the house (where he won't be smelling and obsessing over them) and just let him recover.

It's great that he is getting calmer around you.  Since you suspect he is male, and he is clearly not happy about friends right now, I would recommend just leaving him on his own and working on warming him up to you.  He doesn't need cage mates, but the better the relationship between you and him, the easier and happier his life will be.

Hope I helped, please let me know if you have any other questions!
-Tam