Wild mouse hybrid babies!? Or delayed conception?

Question
QUESTION: i had gotten 2 white feeder mice both females from someone offering them for snake food, i was told either could be pregnant. well one i named momma was and soon gave birth and before i even noticed she gave birth they were all dead and she was pushing them out and then dragging them back in to her nest, the whole time her female cage mate was in with her.
well i was upset i didn't have any mice to add to them so i proceeded to go out and purchase 2 more fancy mice both female from a pet store. i also purchased a very large 3 level cage.
soon i noticed momma was once again showing a very large belly, now i had checked and double checked to make sure all the mice were females and I'm pretty sure they all are.
she has since given birth again, so i have a few questions i hope you can help me with.
1. when i went to a pet store the clerk informed me to watch out because a female mouse can hold males sperm for he said either 3-6 months i cant recall which it was but i had never heard of this before and even with looking it up online it said no such thing. so with the fact I've checked and don't see any males in my cage is he correct? is that how she developed that second litter?
2. when she gave birth to her second litter, 2 of the other females took over her nesting box the same day she had them and soon i noticed the babies all showing up dead again, i had supplied them with 3 nesting boxes so there would be enough. you have said to leave the females in with her as they would help but they just seemed to be killing off all her babies, do you know why?
3. i proceeded to move the nesting box to the lower level of the cage and block off all the other mice, i assumed all babies had passed so after 2-3 days i turned the box to take a peek (nesting boxes are clear plastic) and i see a ton of dead babies but finally momma moves and i see one tiny dark pink baby moving around, woo hoo yay! I'm now on day #4 and I'm not sure how long to leave those dead babies in the nesting box? and how to go about it where i don't disturb her any more then what has already happened.
I'm so worried she will kill that last baby, as she is a very nervous mouse, and doesn't appear to be that great of a mom as she spends alot of time sitting on top of the nesting material that is on top of that last baby, any advise on how to go about working with her and the new baby and the rest of the mess.
4. my last question actually has to do with just one of the females i got, the other mice seem to pick on her and harass her alot, some even nip her back end, she is extremely sweet and is very slow moving acts nothing like the others is this just her personality or was she injured or maybe born differently that she doesnt act the same and she is on her own most of the time.

I'm sorry this was so long and I'm sure i didn't follow some of the rules i have read in the past on your site, like moving the nesting box and peeking at her, i just didn't know what to do when all the females turned on them and i couldn't bear to hear them squeaking and being thrown out of the nesting box still alive but dying.
thanks again and any help would be great.

ANSWER: Dear Regan,

Oh dear, what a situation : ((

I have absolutely never heard of a mouse retaining sperm. When I search online I find a few references, none from experts. I think it is a myth. I will send the question out to some of my knowledgeable contacts and see if anyone has heard of it. I will update if anyone has anything interesting to say.

Are your mice in a wire cage, or another type where a wild mouse could get in? Even if your mice can't get out, a wild mouse can fit through the bars of the average mouse cage, let alone hamster cage. Wild mice are tiny, and slim enough that they can fit through any crack that their skull can fit through. I had a sudden, surprise litter of ten babies in my cage of five virgin girls once; it's actually quite common. Half-wild mice can be pretty crazy, so it might be for the best that they didn't survive.

Mother mice eat babies for several reasons.

1. If the babies are sick or defective. This mouse may just have a genetic defect that means none of her babies are healthy, but she is smart enough to know it. Feeder mice are not bred for health or longevity, so any health problem can turn up. Maybe she even feels instinctively that half-wild mice are wrong.

2. A first-time mother can get confused. Maybe this one is a slow learner.

3. If a mouse thinks she is in an unsafe situation she will often eat the babies because (instinctively) it is better just to get that energy/protein back into her body to use for babies when it is safer. She may feel unsafe because of stress due to noise, other pets, bright lights, unfriendly relations with her cage-mates, being held or the babies being held, cage being cleaned, etc.

The other mice may kill and eat the babies for some unusual psychological reason; or for the same reason as the mom. If you were going to breed on purpose I'd say separate them next time. I hope there is not an accidental next time.

Yes, take the dead ones out if she hasn't eaten them. If they rot in there the big mice can get sick.

As for the timid mouse getting picked on... that's tough. Yes she might be a slow, calm mouse. My mice are show mice and they are bred to be extremely calm, sedate, and slow. In fact they will often just sit in my hand. Other mice are nuts and run all over the place. So it can definitely be genetic. I have found it interesting over the last decade to watch the personalities of my mice from my breeder get sweeter and sweeter-- if maybe a little dumber? Or, she could be sick. A visit to the vet could help you figure that out. But if the other mice are being mean, that's very hard for her. My line is if there are actual bites that draw blood, the mice should be separated. Is there perhaps one other mouse who isn't mean?  You could separate those two out. If not, there is only one thing I can recommend to try before separating her alone. Get another cage. Separate the mice into two cages, next to each other, for a week (put her in the smaller one), until their nice mouse smell is strong enough that they will feel very territorial. Then put a drop of REAL vanilla on their rumps and necks and out them all in her cage. If there is no serious fighting after two days, thoroughly clean out the bigger cage with something nontoxic but strong-smelling like Dr Bronner's liquid soap. Boil accessories (or scrub in hot water) and don't yet re-use anything not washable. Put them in and see what happens.

If she does have to live alone, she must live near the others so they can talk. They seriously do! It's just too high for us to hear. And she will need at least an hour of your physical attention per day. She can be in your sleeve or on your shoulder as you do something else, for part of the time. Face time is good.

I wish you and your mice the very best of luck.

squeaks,

Natasha
<:3  )--~

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

QUESTION: yes my cage is a wire cage, its actually a large rat cage. i considered the fact of a wild mouse getting in, but just seemed odd that out of 4 females that she would be the only one once again with a new litter.

so if she does still have one baby still alive how long should i wait to clean the nest or the cage out? when i check later today ill remove all dead babies that are left if i find any. there is so many different ideas online, some say clean the cage but leave the nesting material alone, and to clean the nest only after 2 week. is that right?

Answer
Dear Regan,

We had five girls who lived together in a converted bird cage that they could not get out of. One day, far more than three weeks after they moved in, one of them gave birth to ten surprise babies. The others did not. I guess she was the flashiest mouse! They went into a 30 gallon aquarium when we cleaned the nest. Yours must go into a tank as well, so the baby can't escape.

You can disturb the nest when they are a week old. Make sure you take mom out when she is out of the nest anyway. Save a little of the nesting material. Rub your hands in the dirty litter before you handle the baby. You should also start handling the baby, if possible twice a day, at that point anyway. Put them in a safe container like an aquarium, putting the bit of nesting material in the nest, and put mom back in asap. If it is a hybrid baby, it will never get big enough to live in the wire cage. I thought our girl (the only one of ten who got tame) was safe in her cage and it turned out she was getting out at night, and one day didn't get back in because the mouse sitter's cat chased her down the stairs.

As for taming it.. really, hold it twice a day (only a few minutes at first). First generation hybrids are notorious for being difficult.  I don't know if ours could have become tamer if I had been giving them more attention, but I was nursing an abandoned kitten at the same time, who took all my attention. The one who became tame did so spontaneously on the same day that her sister decided to be crazy and not want to be held. I let the sister go on a beautiful day in the woods, and kept the one who suddenly decided to crawl into my hand. Hopefully yours will turn out like her. And you won't make the mistake of keeping her in a wire cage like I did.

Please let me know what happens. ESPECIALLY if it turns out the baby is not a hybrid! I am expecting it to be brown (actually, agouti). If it is not, I really, really want to know.  I spoke with a number of mouse people and vets, and did get some at least second-hand stories of strange mouse litters being born more than three weeks after the male had been removed. Please let me know how this baby turns out!! You will know in about ten days.

squeaks,

Natasha
<:3  )--~