tom cat bullying one of his sisters

I have 3 cats - 2 year olds - one tom and his 2 sisters
They all used to get along fine until recently when Isaac has started bullying his sister Delilah, he chases her at every opportunity and causes her to run away.
I find this strange, and upsetting because he doesn't do this with his other sister
Can anyone offer me any advice ?

Hi becsmum,

When you say Tom Cat do you mean he is an un-neutered male? That might be the reason he's bullying his sister. Tom cats are driven by their hormones and will pester female cats, whether they are spayed or not, and fight with other males.

Best thing to do is get him fixed as soon as you can. How about the girls, are they spayed?

If you let us know where you are, country and state, we could help you find some low cost spay and neuter clinics in your neighbourhood.

No, all three have been neutered and have been happily getting along until just recently ! ?

Has anything changed at home recently? New pets or new pets next door? Do they have outdoor access or are they indoor only cats?

Sometimes another cat in the neighbourhood, even a passing stray that they see through the window, can cause them to redirect their aggression towards each other.

For cats that are mainly indoors a Feliway diffuser can help. It gives off a smell similar to the "calm" hormones a cat emits. You need to keep the windows closed for it to work properly though.