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Pet Rats/Sisters-female rats-aggression onset


Hello All Experts, Debbie,

I adopted my two girls Lexi and Willow just over a year ago (they are 18 months now). They have been together since birth, and the Mom of Lexi and Willow was rescued from a 'hoarder' situation. I don't have any information about the Father. When another lady rescued the Mom, she did not know she was pregnant. So my vet assisted in finding the new baby ratties homes.  

I spent the first while getting to know my girls when they were fostered at my vet's office (exotic vet, very good).  After a few months of visiting and playing with them, I decided to take them home for good. I have had 4 female rats before these two, with a slight break in between. Lexi and Willow live in an amazing critter nation home, and there is plenty of room. Everything was going well up until about the middle of February of this year (2015). This is where I noticed some changes in their behavior.

Initially, Lexi (who I would suggest is the alpha) started to bite at Willow's hind end, I would find little scabs and chunks of hair missing when I came home. One of the worst bites occurred when Lexi and Willow were out during playtime.  The fight quickly ensued and I did a no-no of reaching in. Lexi came away from Willow, slightly tagged me (no skin break) but poor Willow had an inch gash (open and red) on her hind end/middle back. Lexi continued to approach Willow, but I took Willow and secured her away in the cage. At first I thought this was a hormonal surge, because there was nothing for them to fight over (no food, no toys, just me hanging out with them).  I separated them until Willow's wound healed up completely, because Lexi was always trying to see it, and was too interested in it.  And of course Willow would always flinch, squeak and bolt if Lexi got near her hind end after this.  After about 2 weeks, of being separated, I cleaned their house well, and re-introduced them. There was no pilo-erection, and no sidling, just a little play fight that started to get too rough, so I did the water gun squirt and they both separated. After this, they cleaned and even cuddled.

Lexi tends to sidle and her hair gets puffy if she's going to become aggressive, although not every time.  So for about 2 weeks, there was no further aggressive behavior. They slept in the same hut, groomed, and also were fine with alone time on different levels of their large cage.

Then at about the 16 day mark of being back together, I arrived home after a long work day.  Lexi was up on the side of the cage bars hanging there, and Willow had just surfaced from the cloth cube. Usually, they both climb the cage and crawl over each other when I walk in the door, without any fighting. As Willow was going down the ramp, Lexi came off the side of the cage and pursued Willow. I didn't notice this until later, but Lexi's left side pinky toenail was missing (pulled out).  I wasn't sure if Lexi came off the cage too fast and caught her nail or not, if she did, did she associate this somehow with Willow causing the pain (as Willow was the only 'alive' creature in the cage)?  This fight was not good, and they ended up in a ball, then Willow bolted into the cube. I used the water squirting technique to break them up.  When I examined Willow (as she always gets the worst of it), her right ear had a puncture in it (a sharp nail likely) and it was bleeding through to the inside. She had some hair missing on the underside of her hind legs (only visible if she stood up to reach), as if Lexi bit her when she was on her back. I separated them again, to allow Willow's ear to heal. This fight occurred 2 weeks ago now, and they remain separated within the same cage (upper/lower level separation). I allow them to be out with me, and play at the same time, but I do not feel good leaving them alone with each other when I am not there. I now notice that even when Lexi calmly approaches (with no pre-fight cues) Willow grabs Lexi on the sides of her head (like a headlock) pulls her head down and I read it as Willow doesn't  want to give Lexi the chance to get too close.  Prior to this happening, Willow looks concerned and freezes, then starts to wag her tail quickly, back and forth. Willow does stay low to the ground and seems very apprehensive of Lexi even if I am there.  Then, sometimes, Willow pursues Lexi when she runs off to play or bound, but as soon as Lexi turns around, Willow looks scared and runs back to me.  Even if Lexi comes up to Willow, Willow immediately freezes and/or puts her dukes up (front paws).  Willow seems to be scent marking a lot more than usual. Lexi has commonly scent marked before, and still now, to date.  Both girls have not been spayed. Despite this new aggression, they look healthy in their coats, eyes/nose, and their energy level and curiosity is all good.  

I am just stumped as to why this has all started to occur, when they used to travel well together and rely on each other when I wasn't there.  Of course I would love to see them back together, but I am afraid that a more serious injury will occur to mainly, Willow.  I haven't seen anything on Lexi other than a tiny scratch on her outer hind end, and some tail scratches.  I wonder if this is a hormonal surge, or they are just tired of each other!? Of course I would like to see them together again, but not at the risk of one or the others' safety.  I guess my question here is two-fold:

1) Do you have any suggestions as to what is causing this shift in behavior pattern, and what I could try to do differently; and
2) If they end up having to remain separated, is this going to affect them adversely? (the cage allows them to sniff, see and hear each other, the ramp just closes to separate top from bottom level).

Any suggestions you may have, I would sincerely appreciate...
Thanking you in advance,
(Willow and Lexi) -
(Shizzy, Bailey, Addison, Didi and Gylfie across the Rainbow Bridge:)"

P.S. I really do not want to get them spayed now, as they’re approaching their 2 year-old birthday, this  September.

Hi Anne,
Unfortunately, I think spaying would be the best thing to do, although I understand your reluctance. It could be she has an ovarian cyst that is causes her hormone change. But, I see you live in Canada, so you could ask your vet to try treatment with a drug called cabergoline, which is often used for hormone problems. Maybe that will help.

Otherwise, I think it is okay to keep them separate, and only let them interact when you are right there to supervise.

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Debbie Ducommun


I can answer any questions about pet rats, but you will probably be able find answers to simple questions more quickly on my website at If you have a life-threatening emergency you can try calling me at 530-899-0605. I am not usually on the computer on the weekend.


I have been "The Rat Lady" since 1985 and am recognized as one of the world's experts on pet rats. I have 3 published books and already answer lots of questions about rats daily.

President of Rat Assistance & Teaching Society

I am a monthly columnist for Pet Business magazine, and my writing has appeared in other magazines. I have 3 published books.

BA in Animal Behavior

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