Why wont my mouse mate & tail rattling

Question
I just introduced my new doe mouse Aurora to my male Socretes first. They did nothing except act like girlfriends. I have had socretes in cages with many different females before and he has never mated with them. He acts like a female actually. I put him in the cages I have with my mice that have been impregnated by my other male Crito and he literay helps groom and socialize the pups. I keep Crito and Socretes seperate so I don't think it's a dominance problem, I keep Socretes in with my regular does. I have tried on many occasions to have socretes with one female at a time for at least three weeks time, and no pregnancies. Youre probably wondering why am i trying to mate him he is just a mouse. The reason is because he has an amazingly sweet and helpful personality, and Aurora because she has the same personality and they both have beautiful colors! The two just laid there grooming each other for HOURS!!! I placed her with Crito today and once I got home I checked for a plug, I believe I see one but not completely sure. What is Socretes
problem? It can't be age because I personally hand reared him from a litter and that was 12 weeks ago. What could it be?
Now about the tail rattling. I just placed Aurora into a solitary nursery cage. She is very friendly when I hold her and she licks my finger tips. Put when I walk by her cage I can hear her rattling her tail inside her neat, why is this? I've been told it's a warning of aggression but she let's me pick her up and hold her. What could it mean?

Answer
Hi Rei,

There could be a few reasons for Socretes being so clueless about the birds and the bees.  Since you already know about plugs, I'm going to assume you've sexed him correctly.  :p  First, he could just be too young to have it really figured out yet.  Just like in people, mice mature at different rates.  12 weeks is a totally reasonable age to start exploring, even though I've never personally had one wait that long to figure it out.  Maybe he'll get the idea later on in life?

Second, some males just never get it.  This could be a really great thing for you, because it means you can leave him in while the pups are growing up.  Mom can have a little help, you never have to worry about him getting her pregnant back to back, and current research points to the benefits of having a male role model on the social and mental health of developing pups.  Usually this is hard to get without re-impregnating mom, or the dad eating the babies.  But you've already got a perfect daddy that you don't have to worry about right here.  It could be a good thing.  :)

Third, some mice can be hermaphroditic.  It's possible he has the equipment but it either doesn't function correctly or he doesn't have enough hormones to feel motivated toward the deed.  He could also just be sterile.  Point being - there could be a physical reason for him being feminine and not sexually interested.  I wouldn't put this as a high risk, really, but it does happen on occasion.

Lastly, have you tried putting the female in his cage, instead of him in hers?  Some males won't mate until they're sure they've peed all over the entire cage and verified the territory is definitely theirs.  He doesn't sound like a very bucky male, and if you've had him in with a female up to three weeks, I wouldn't put this as very likely either.  It's a possibility, though, and the last I can think of.

As far as the tail rattling, it's definitely a sign of aggression every time I've seen it.  It might be that she doesn't recognize you through the cage, so she's announcing that the nest is hers, but once you put your hand in she realizes it's you and calms down.  If you think it's stressing her out too much you could move her to a less frequented area and see if she stops.

Best of luck, and congratulations on your possible pregnancy by Crito!  :)
-Tam