I recently adopted a cat from a shelter (she was in a foster home). She has come along very nicely with us but seeks every opportunity to attack my other 2 cats (both fixed and extremely mellow and passive) I have tried everything to discourage this behaviour to the point that the adopted cat knows when she has done wrong and promptly goes up to the room I have put her in for a time out. I am now forced to separate her completely which is not fair to her. Due to shelter issues I can not return her and I adore her but is there any hope she can change?:confused:

Actually she will in time. You're going to have to put up with it for awhile, it's simply cat culture and them sorting out who the "Alpha" cat is (sounds like she is and she's just proving it to the others.) In time they'll become friends, it just takes time and patience.

Agreed with Ryana.

It was a good call to make assign their own territory.

With strays, they are not used to sharing their space. They behave as if they have to draw a boundary every time.

When I first met my present stray, she bit my partner and I almost all the time to set her boundaries. It took about 8 months before she realized she could do less severe strategies to instill her boundaries. Eventually she didn't need to have to set so many boundaries.

With other cats, they got to have their own territory.

Strays require patience and lots of love and understanding but it pays off in the end

I have a siamese kitten and it was a stray. Siamese cats are known for being the most aggressive cats and he is a male which makes him even more aggressive since he's not neutered and he was a stray so he naturally thinks that he has to fight his way with everything. When a kid is at school and someone bullies him it belittles him so when he grows up he will most likely bully someone else so he can feel revenge for the time he was belittled... can be used for cats too... cats especially strays could have been terrorized by some other animal probably a predator and so they felt helpless and now that they are in a better environment they in return are aggressive. My kitten had siblings that were eaten by some local wolves and he had to deal with that the first 6 weeks of his life so it didn't help him at all. ANything is possible in causing the aggressiveness of your cat.

LOL! Clumsy thumb hit the enter button as I was rating Pennybots answer. It was right on the money. I have an abandoned cat (now two) who's mother had kittens. The owner of the mother didn't want the kittens, so they moved and left the whole family behind. Sad part is they told the story to the neighbors. Anyway, my stray was very unfriendly and confrontational with both me and the cat I already had for a few months. Now we are all best buds. He's the most loving animal in my home and he and my other cat are inseparable.

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Originally Posted by thespababe

I recently adopted a cat from a shelter (she was in a foster home). She has come along very nicely with us but seeks every opportunity to attack my other 2 cats (both fixed and extremely mellow and passive) I have tried everything to discourage this behaviour to the point that the adopted cat knows when she has done wrong and promptly goes up to the room I have put her in for a time out. I am now forced to seperate her completely which is not fair to her. Due to shelter issues I can not return her and I adore her but is there any hope she can change?:confused:

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I'm going through the same thing myself. I recently adopted a cat from the shelter who'd been caged since August. It'll take time, patience and lots of love. He or she will need to learn he or she can trust you and feel safe. Its good to reprimand bad behavior by using a stern voice and to reward good behavior with treats and praise. I've thought about using the pet carrier as a time out but decided against it due to his being in a cage for so long. If you cat is spayed or neutered the aggression will ease a bit as well.

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Originally Posted by thespababe

I recently adopted a cat from a shelter (she was in a foster home). She has come along very nicely with us but seeks every opportunity to attack my other 2 cats (both fixed and extremely mellow and passive) I have tried everything to discourage this behaviour to the point that the adopted cat knows when she has done wrong and promptly goes up to the room I have put her in for a time out. I am now forced to seperate her completely which is not fair to her. Due to shelter issues I can not return her and I adore her but is there any hope she can change?:confused:

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You should try to let them work things out. Seaperating them when she is bad is good, but you can't be a mediator all the time. She will find her place in the group eventually. It will take time and patience. The other cats will put her in her place when they become aggravated.