I'm at a bit of a loss. About a month and a half ago, we rescued a 6 year old male tabby named Niko. We brought him home, and put him in his safe room, but we really took introductions to our resident cat too fast. This led to her hating him. She would hiss at him and chase him until he hid under the bed. This went on for a while, until we decided to go through re-introduction. We put him back in the room, did scent exchanges, site swapping, feeding on opposite sides of the door, etc. They got to a point where they could eat together while seeing each other and being about a foot away from each other, so we decided to let him into the living room again. She would still hiss, but we'd redirect her with toys, and reinforced positive behavior around him with treats, and that worked very well. Today, it seemed to be going well, but then went downhill.
Resident cat walked up to Niko while he was on the cat tree, sniffed his tail, and jumped down. No hissing, nothing. Then, a few minutes later, Niko was on the floor, and she walked right by him, again, no hissing. We were cheering for her! But then, Niko became the aggressor. Right after she walked by him, he followed her, and stood over her in a dominant kind of way. He then tried to paw at her, and she ran away. For the rest of the night she's been back to square one, and actually even worse. About 20 minutes ago, resident cat was on the cat tree, and Niko was on the ground. Both of their tails got bushy, and she started growling LOUDLY. Niko looked like he was about to attack her. I've never heard her growl like this. I redirected Niko into the bedroom with treats and that's where he is now. I'm at a loss. It seems like Niko is trying to be the dominant one and resident cat is NOT having it. At this point I feel like my only option is getting both of them on a calming medication and going through re-introduction once again, or taking Niko back to the shelter. They both seem like very dominant cats, and I'm so worried that it'll just never work between them. Any advice would be greatly appreciated.
Note: I tried the multi-cat Feliway diffuser, and it made Niko worse. He began spraying, despite being neutered, a few days after the diffuser was plugged in. Another thing that is most likely causing his dominance behavior is that he had not been neutered until he was 5 years old, about a year ago.
Resident cat walked up to Niko while he was on the cat tree, sniffed his tail, and jumped down. No hissing, nothing. Then, a few minutes later, Niko was on the floor, and she walked right by him, again, no hissing. We were cheering for her! But then, Niko became the aggressor. Right after she walked by him, he followed her, and stood over her in a dominant kind of way. He then tried to paw at her, and she ran away. For the rest of the night she's been back to square one, and actually even worse. About 20 minutes ago, resident cat was on the cat tree, and Niko was on the ground. Both of their tails got bushy, and she started growling LOUDLY. Niko looked like he was about to attack her. I've never heard her growl like this. I redirected Niko into the bedroom with treats and that's where he is now. I'm at a loss. It seems like Niko is trying to be the dominant one and resident cat is NOT having it. At this point I feel like my only option is getting both of them on a calming medication and going through re-introduction once again, or taking Niko back to the shelter. They both seem like very dominant cats, and I'm so worried that it'll just never work between them. Any advice would be greatly appreciated.
Note: I tried the multi-cat Feliway diffuser, and it made Niko worse. He began spraying, despite being neutered, a few days after the diffuser was plugged in. Another thing that is most likely causing his dominance behavior is that he had not been neutered until he was 5 years old, about a year ago.
