I have two female cats, a brown tabby (3.5 years old) and a black/white (3 years old). I've had them since they were kittens. Both have been spayed. I've noticed some interesting territorial behavior recently, and while I think it's normal, I want to be sure.
The black/white has always been high-strung -- the vet took one look at her and said "This one will become the dominant female". So I figured it was inevitable. But I've never really seen any territory struggles -- they get along great. The only times they don't get along is when the black/white has too much energy and starts chasing the other one -- it stops when the tabby starts hissing. Then they're back to being friends a minute later.
A month and a half or so ago, I started to notice my two going at it more than usual. This time, the younger black/white was wailing at my other cat and hissing. Hard to describe the wail -- starts kinda high, then goes really low, almost like a growl but not quite. Tails fluffed out, aggressive posturing. I step in and separate them, but they just walk around me to keep an eye on the other, hissing and posturing. Finally I get them separated and force one of them upstairs so they can cool off. A few minutes later, they're all normal again, but initial contact is very timid, almost like "I won't do anything if you won't."
This happened repeated times, and I never could understand a source for it. Usually I would wake up after having fallen asleep on the couch while watching TV and the issue is in progress.
The last two times this has happened, I found that an orange/white cat is involved. I'm not sure if it's a male or female, but I've noticed it out on the deck. Both times when I noticed this cat, I noticed that my black/white is not involved in any interaction with the other cat, other than maybe looking at it curiously. It's my tabby that is hissing at it, or posturing, and tonight she jumped at the window at least three times while hissing, trying to attack.
I figure that's normal for a territorial dispute -- my tabby is letting the other know in no uncertain terms that this is her domain. However, when the orange/white finally left, and my tabby was walking back to the interior of the house, she ran into my black/white, and they started posturing. Well, mostly it seemed the tabby was posturing, but I'm certain there was hissing from both.
Naturally, a few minutes later, all was back to normal.
I think an explanation for this behavior could be that if this were in the wild, normally there would have been a fight between the tabby and the orange cat, and after winning the fight, the tabby might expect to be challenged by another cat, and so it stays ready for action to thwart any rebellion.
I guess my main question is -- it seems like the tabby is definitely still the dominant one, since it appears that she is busy protecting her territory, so I'm just wondering if normally cats will continue to act aggressive even with other cats they know, even after the first threat is gone. Basically, is this normal, or anything to be concerned about?