Trouble In The Gerbil Cage

[Darkie100]

We have three female gerbils , bought at the same time who have shared the same cage for a year with no problems at all. Unfortunately one as started to attack another and and appears to have bitten her quite badly. We have put the aggressor in another cage and will take the victim to the vet in the morning because she is obviously traumatised and is hiding in the corner of the cage(though I did manage to coax her out for a sunflower seed)
We were led to believe three gerbils would live together quite amicably.Is this a case of one asserting dominance?
Has anyone else had experience of this behavior, and if so ,what was the outcome?

[wildwood]

I believe the females are more territorial than the males. Maybe two became friends and ganged up on the third one. This sometimes happens with other animals too.