Cat aggression towards littermate after adoption

Hi! I'm hoping some of you lovely people can give me some advice.

I have had Porter and Hugo, two littermate brothers for three years. They are not super close (they don't cuddle or groom each other) but they seem to like each other and stay close to each other. 

Until recently, when I adopted Gabriel, a 4 year old boy.

Ever since, Hugo has hissed and growled at Porter whenever Porter gets close. Porter can't figure out what to do; he's terrified of the newly aggressive Hugo, and of the strange scent in the safe room. Gabriel is still in his "Safe Room" and hasn't come out, though he clearly wants to meet the other cats and cries whenever he hears them. I've put Hugo into his own "Safe Room" and am letting Porter roam the house and sniff at both doors.

Any advice for what to do? I'm worried I've ruined all the feline relationships in my house, and Gabriel just wants to come out and play.

They are all neutered? 

This is a common thing, cats are territorial creatures, when someone new comes along they will act aggressively. 

Try keeping the feliway (or something similar) on 24/7, the more friendly cat vibes out there the better. 

I'm pretty sure you've done your homework because you have them separated. Just in case, here's Jaxson Galaxy talking about introducing cats.

Have you started scent swapping yet? Here's an article from this site with some great tips for getting cats to enjoy each other's company.   

Yes, they're all neutered. If it matters, Hugo and Porter were both neutered very early as kittens, while Gabriel wasn't neutered until he was an adult. However, Hugo's never even seen him, just smelled him!

Would it help to keep Hugo and Porter separated for awhile?

I am also in the same situation. I have two cats who are also from the same litter both female. They're very close as they always groomed each other and more often than not slept side by side.

I have bought home a third cat a few months ago with no change form either, however back then they just around 4 months old. They're around maybe 6-7 months and I bought home a fourth kitten a week ago and they started being aggressive to each other. They were hissing at each other most often during meal times. I had them eat from the same bowl since they were able to feed on their own but that time they won't let the other get close when eating. I also noticed in my case they were being agitated when I have the new kitten out. When I put the new kitten in the bathroom where they cannot see it. They usually calm down and being back to their normal selves until they see or smell the new kitten again.

It has calmed down a bit now but usually flares up again during meal times. Also both cats are not yet fixed.

Hugo is displaying misdirected aggression. He is agitated from the new smells and sounds and is directing it at Porter. It wouldn't help to separate them, unless the aggression turns to outright serious fighting, in fact it may make it worse. Cats HATE CHANGE, and there is a lot of changes right now. Don't make it worse by making more. It's not unusual for Hugo to act this way, time is on your side and is what you need. He needs to calm down and will eventually accept that there is a new cat in the house, my cats took over 6 months to even begin to accept each other. You might start with the introductions of Porter and Gabriel who might be easier to get together. make sure Hugo has a safe place to escape to, preferably high up and easily defendable. You might order some 'calming treats' on Amazon or from a pet site, they help tremendously in calming nerves, I only give one treat, not what they recommend. Hugo WILL come around eventually, he just needs extra love and support from you, and a very gradual introduction of Gabriel to get him used to his new situation. I even bought a cheap wooden screen door which I hung in a doorway (and later patched the holes with colored wood putty) to let them see and smell each other without actual physical contact. I have had cats that have attacked each other viciously get to be friends a year later, it just takes one day at a time and lots of treats to make everyone happy. Good luck, and keep us posted!

Thank you for the reassurance and advice, Di and Bob. Hugo is downstairs now (away from Gabriel, who is in one of the upstairs bedrooms) and behaving normally towards Porter. I have ordered more Feliway so we can have some downstairs and upstairs. I put one Feliway diffuser in my bedroom, hoping that it would lessen the tension up there so that I can sleep in my bed with them tonight. Last night I slept downstairs on the couch because it kept them both calm and away from Gabriel!

I'm at a loss. After being friendly to each other all day, Porter and Hugo are suddenly being very aggressive towards each other once more. I'm starting to think rehoming poor Gabriel might be the best option. This is really stressing me out.

I know it seems stressful now; but it's completely normal for cat introductions to take weeks to even a few months to work out.  Every cat is different; but these things do take time. The cats can also sense when you are tense and stressed and they will feed off of that.  So don't be discouraged.  It might take a little more time and trying some different things (like Di and Bob suggested above) but I wouldn't lose hope yet. 

It's often one step forward two steps back. Make sure they don't have to compete for things like food and there are enough high places and places to hide

The boys slept together and then united over their favorite thing, an open window (with screen, of course!) This was even after smelling and hearing Gabriel, so I think I'm just overreacting to every little territory spat.

Gabriel goes to the vet today, so we'll hear if he is sick or not (my instinct is he's got a little something, but he seems perfectly happy.)

So you have visuals, here are my two tiny house panthers, Porter and Hugo.


And here's pretty Gabriel:

Yes, sometimes the smallest incidents seem worse than they are when you're not used to them happening at all.

How did the vet visit go?

Unfortunately, Gabriel might have ringworm. I noticed the two little bald patches on his legs earlier. The light test was negative, but the vet suggested a skin culture. I am SO hoping it's not ringworm! The shelter offered to take him back and treat him, but I'm worried that might scare him, and I'm still holding out hope that it's allergies and the switch away from the (terrible) food the shelter was feeding will help. No interaction or room switching for the boys until the culture comes back.

On the bright side, Porter saw Gabriel in his room today as I was coming out the door and did not hiss. Both Porter and Hugo are sniffing at the door a lot more now that I'm rewarding them with treats if they don't hiss or run away.

My parents have offered to help me install a screen door to Gabriel's room. When Porter and Hugo are ready, we'll do that! I think it will help them to see him (he's smaller than both of them, even if he's a bit older). Plus, I think it will make Gabriel very happy.

Progress today as Hugo got aggressive then stopped without my intervention (I was in Gabriel's room). I feel really happy that Hugo and Porter aren't fighting!

I'm planning to install Gabriel's screen door as soon as the boys walk by his room without hissing at each other. Porter has tried to get in Gabriel's room; I think he's much less afraid than Hugo.

Gabriel is taking to the food change like a black hole. It's good-- he could stand to gain some weight.

Gabriel got out today and gave Porter a kiss on the nose. Porter was startled but didn't hiss or growl. I think this will wind up being a very easy introduction!

katilizzy said:

Gabriel got out today and gave Porter a kiss on the nose. Porter was startled but didn't hiss or growl. I think this will wind up being a very easy introduction!

Click to expand...

   Awww, cute!

Porter and Hugo were able to walk by Gabriel's door without hissing and would eat cat treats right by the door, so I installed a screen door this weekend.

Porter is back to hissing, sometimes right by the door. He will still eat cat treats right by the door. Hugo is a little more fearful and will only hiss from across the hall or run very fast by the door. Neither of them have been growling or attacking. Gabriel responds to all of this by ignoring it, meowing at the other cats, or even purring at them! He's kind of a weird cat. Gabriel won't eat cat treats at all, so I just tell him he's a good boy.

I feel a little bad for Porter and Hugo because they haven't been sleeping at night, just watching Gabriel from the end of my bed like he might attack! And I feel bad for Gabriel because it must not be too fun being hissed at from behind a screen like a zoo attraction.

Is this normal? Does it sound like it is going okay?

There's still a lot of hissing from Porter and Hugo. I feel terrible for Gabriel, who wants out of his room so badly!

How long has it been since you brought Gabriel home?  It really is normal for these things to take time with some cats.  If you remain calm and confident that will help them sense that everything is ok.  id you get the results of that ringworm test?

Finally got initial results for Gabriel's ringworm test back, and it was negative! I'm so happy! I started letting him have supervised visits with Porter and Hugo, which are going well. Everyone mostly ignores each other,with some mild hissing from Porter and Hugo.

I've been trying longer visits with Gabriel. Everyone mostly ignores each other or sleeps, however Hugo randomly gets pretty aggressive. I have to take them all with me when I go home for thanksgiving, so that should be interesting...