Lonely hammie

Question
I have a couple of questions. First I'd like to thank you in advance for take the time to answers everyone hamster questions. There seems to be limited resource of hamster info online.

I have a family of Robos. I started with two hamsters. The pet store said they where both boys and that they like company. I fell for it and bought two. Well they had babies during the summer. My boyfriend and I where very careful when caring for Mama and her babies. We separated Papa ham to his own bachelor pad and seems happy enough. After 5 weeks we gave away the boy babies, (by this time we read how to figure out the sex). The mom and 3 girl hamsters are left. They live in a big cage with a "lazy lookout" and all. a pretty nice living if you ask me!!
All the babies seemed identical and healthy. Now after 4 months there is a big problem! The mom and 2 girl hammies seem to have decided to pick on the fourth hamster!

At night they wont let that hamster run on her wheel.
the fourth ham has to eat away from everyone else.
They fight her whenever they cross paths.
and worst of all they bite her tale and only her tail.
The hamster doesn't seem like its in pain but her tail is all chewed up. Now I know that its just a surface wound because its already scabbed.
The bully hamsters do all this to the fourth hammie but when it comes to sleeping they all sleep on top of each other like a cozy little family.

Why the change in behavior?

I separated the poor hammie and it is now alone in my trash can for now (with fluff, food and water).

What do you think of my situation?

And do Robo Hammies really like to be with a friend?
Should i try to separate the fourth one with one of her sisters? or will that sister still pick on the fourth hammie.

the fourth hamster is the smallest of the group. So i guess its that runt but it wasn't always the runt.


thanks for reading,
kassandra  

Answer
Dear Kassandra,
thank you for your question.
You will need to separate all the hamsters. Roborovski hamsters live in pairs in the wild, with one litter until the next one arrives. Sometimes the females stay to help with raising the next litter, but usually they are chased away. That's why they don't accept another hamster of their own sex, at least not permanently. If you take the runt of the litter out, they will pick on the next one, the weakest will always get bullied.

They will be fine on their own and apart from that, it's almost impossible to introduce dwarf hamsters to each other after they have been separated.
I hope I was of some help to you
Jennifer