Aggressive Female Rat

Question
QUESTION: I have a female rat, Cleo, that is about 14 months old. Shes always been a sweet girl with a very determined personality. She always wanted to be a part of whatever was going on outside her cage, and responds to her name (as well as any talking noise). Once out of the cage, she goes into what I call her "I'm on a mission mode" and tries to sniff out anything new. She never scent marks, but rubs her back and side along a wall if she can. When I first got her with her sister(Luna), I had two other rats at the time and the four of them got along pretty well. The only problem was that Cleo would "hump" the other rats 3 or 4 times a day. One of the older females didn't like this much and would fight with her. They were small harmless scraps, barely any squeaking or biting. After the two older rats past on, just Cleo and Luna lived together very peacefully. Last December, Luna died, and Cleo seemed to take it well enough, she just seemed a little needier. In February, I got a new female, roughly 4 months younger than Cleo (Cricket). After 2 weeks of isolation, then general introductions, it became apparent that Cleo's main goal was to hump Cricket any chance she got. Now that they are slightly bigger and more equal sized Cricket has "had enough" and will pin Cleo down to stop her. When they do this...they actually fight(screaming and ripping out fur), and the longer they have been living together the worse it's gotten. I decided to separate them and just let them play together when I bring them out of the cage (twice a day for about an 1 1/2 hrs). It seemed like it started ok, but now both of them seem depressed and don't like sleeping alone. But any time I put them back together in a cage, they fight. Now Cleo's fur has started thinning and she's showing gauntness as well. There is a neutered male (only one in the house) in another room of the house (they have all played together) but Cleo humps him as well and he fears the both of them to the point of cowering in my hair when they all play. I can't seem to find a solution for her that doesn't leave them all in isolation. Her vet checks have all been normal and healthy as well, so I am at a loss of what to do.

ANSWER: It seems to me that Cleo has always been your "alpha" rat, always making sure the other rats in the house knew who the boss was at all times.  She would hump them often as reminders perhaps, but the other rats I'm sure just accepted Cleo as the alpha and were good with it.  Remember that the other 3 rats and Cleo all pretty much "grew up" together.  Rats are much easier to introduce when they are babies.  Now, Cleo is older and it is often much harder to introduce a newcomer to an older rat (if depends on the older rat's personality).  Regardless, in almost all cases, whenever introducing a new rat to either a colony of rats or a single rat, the fight for dominance must occur.  Cleo, I'm certain is trying to re-establish herself as the alpha rat to the newcomer.  It sounds as though the new one is pretty dominant rather than submissive herself, and so they are trying to fight it out.  On average, this can take a few days or perhaps about a week, so I'm not sure why this is going on for so long with your rats.  It is of course possible that they may never work it out if you have 2 very strong personalities in there.  It is up to you if you want to continue to allow them to try to work it out, but please always under your supervision as it sounds like it could get nasty.   Don't try to intervene in the fights unless they are starting to get bloody and violent.  If after a period of time there is no sign of change, I would suggest separating them and perhaps adoping 2 very docile rats, one for each of them, to share life with.  You would still see the fight for dominance at the beginning, but a docile rat would usually succumb quickly and peace would be established.  Good luck...let me know what happens and what you decide to do.

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

QUESTION: I think you may be right about having two dominant personalities. I ended up buying a much bigger cage for them with two more levels on it than they had before (they had a ferret cage before). The added space seems to help because I feel like they can "get away" from each other when they want to. The fights seem to be slightly more subdued but after watching them for a couple of hours, I notice that they definitely seek each other out for a fight. They trim each others fur a lot and are very active (hopping over each other to pin the other one down). Cricket also "screams" for no reason. For example, if she knows that Cleo is going to flip her over soon, she will scream as she is being groomed and then try to groom Cleo's belly. I know it doesn't hurt her, because she is a very vocal rat in general (chirps like a bird, not bruxes, when she likes things, whines when shes lonely). Cleo also spends a lot of time running her side along the bars of the cage. She sort of scoots along when she does this. I have owned many rats in the past, but none who have as quirky behavior as these two. Could it be that they just like to really wrestle and the fur loss and gauntness I see in Cleo be because they like to fight?

Answer
OMG your response made me giggle...Cricket screaming & chirping and whining! I've never had a rat that did any of that (although one of my rats actually snorts!) First of all, AWESOME idea getting the larger cage.  I'm mad at myself for not suggesting that.  All rats need space to roam and find isolation when they need it.  Cleo and Cricket though seem to have a love-hate relationship, so to speak.  Not that they hate each other but it seems like they rather enjoy the rough-housing and yet they seek each other out for comfort and grooming.  Like humans, that is just their relationship based on their personalities.  And I guess as long as they are not harming each other physically, that is ok.  I would bet either one of them would terribly miss the other should they be separated.  

One last thing...you say you've never had rats with such quirky behavior as these two, but really, don't we also as humans each have our own "quirks", some more eccentric than others?  Your two ratties are both very animated and you should have hours of enjoyment watching them as your entertainment.  My rattie that snorts, Ariel, now that is just weird!  But not only that, she is the craziest most hyper rat you could ever imagine!  She disappears like a lightning bolt any chance she gets during free play, but then she just stands there around the corning staring at you with her huge bulging eyes and just simply lets you pick her up and take her back...she never "escapes".  My rat Zoey is a "pack rat" and stashes any piece of trash she can find in her hideaway, and my rat Ziggy had an attitude like she's so much better than the rest...go figure.  They're each and every one so different and quirky in their own way, which makes each one so special.