We have had our 2 gerbils for almost 2 years now. Originally, when we bought them we did have to introduce them via the split cage method (due to a death of one of the original gerbils that was still "under warranty". The split cage method worked wonderfully and took less than a month before they were living without the cage split (if my memory serves me correctly). We've had no problems up until about a month ago where one started biting the other one's tail. The fighting is only seeming to escalate. It seems to be more frequent and now we see that blood is being drawn. They are both females...approximately the same age. If I had to guess...it could be possible that the one doing the biting is a slightly younger than the other one being bit. Nothing has changed....their cage hasn't been moved to a new spot and nothing new has been introduced to the cage; we haven't changed brands of food; etc. If you can give us some advice, that would be wonderful.