I already had two cats, a twelve year old girl and an 8 year old boy, when a little black stray moved in. I have had him for a year now, he has been neutered and had his needles and to begin with everything was fine. Now he has started bullying my girl cat and I have to keep them virtually separated. She has a look in her eyes as though she is hunted, which she is, I suppose. How can I stop the bullying, I don't want to part with the young boy, I love them all to bits. Any help, please. I have tried Feliway, which helped to begin with, but doesn't now.
I really wish that I could help you. I know that cats can be dreadful bullies - my two bicker all the time but are evenly matched (boy/girl siblings) and I tend to just leave them to it.
Try Googling 'bully cats and you should find plenty of information - not sure if it will help or not.
I tried the Feliway to help my two to get on better - it didn't help at all.
Cats are territorial. Try to help them define their individual territories by, for example, having one cat's basket upstairs and the other one downstairs.