Up until less than a year ago, my wife and I had ever only had one cat at a time.
From just after we married, until late 2011, it was Felix, a tomcat that we think was at least part Maine Coon. (He was too small to be a full-blooded Maine Coon, but he otherwise seemed to have all the traits of that breed.) He liked other people, and even dogs, but he hated other cats, and would get very upset if approached by another cat, or if another cat intruded into his turf.
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When he passed away, over Thanksgiving weekend in 2011, we got another cat within a few days.
Felix's successor is Allie, a female Siamese. Much more territorial than Felix, she hates other cats, dogs and even other people than her own. She hides if strange people are in her home, and she growls and hisses at other cats who intrude into her home, and has reacted similarly to the few dogs that she's every encountered.
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Around April of last year, an orange tabby that had been a semi-stray around my apartment complex decided that he's my wife's and my cat. He started hanging out with us around that time, and by some time in June, he was staying pretty much full time with us. Buddy does insist on being let out for a few hours every day, usually late at night or early morning. he seems to want to b friends with Allie, but Allie wants nothing at all to do with him. He tries to play with her, in a manner common to cats, especially to young cats, and she always responds with hisses and growls and sometimes even screams.
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Buddy has been observed, outside, interacting with other cats in a much more mutually friendly manner. He seems to be utterly baffled by the fact that Allie won't play with him as other cats outside will.
However, Buddy gets very upset, and behaves much as Allie does, to any other cats coming into what he now considers to be his home. he recognizes Allie as legitimately being here, but responds to any other cats that come into the apartment in much the same way that Allie does.