It’s normal. Just don’t jump between them when this happens. My friend’s mom once jumped in between her fighting cats (after this same type of window visit from a stray). They freaked out and one attacked her. Her feet and legs were so torn up, she had to go to the hospital. Not the poor thing’s fault. He was surprised and defending his territory.

Spraying can def still be an issue. I’m not sure why your cats attack each other and think it is worth asking a behaviorist.
Sometimes our cats just get annoyed and need their space and that’s what they do when they are frustrated and under stimulated, esp during winter when we don’t let them out.

We have neighborhood cats come over and wait to play with ours. They get along pretty well. They are all TNR failed rehomes because most people don’t do well with feral/semi-ferals but they are lovely indoor/outdoors now.

Anonymous wrote:OP Here -
Both of my Male cats have been fixed.
(I adopted them from our local county shelter.)

Can spaying still be an issue?

Prob not unless they feel very threatened by the stray cat. Even then, it would also take a long time and lots of exposure to the stray cat before it gets that bad. I agree with the other pps to get some sort of motion activated sprinkler to keep the stray cat out.

*spraying

OP Here -
Both of my Male cats have been fixed.
(I adopted them from our local county shelter.)

Can spaying still be an issue?

I would echo the PP who said scare the outdoor cats away. Your indoor cats could start exhibiting a lot more bad behavior such as spraying. I have watched the cat guy on tv several times resolve spraying issues because indoor cats are threatened by outdoor cats.

They're both amped up from wanting to fight the "intruder" cat. There's nowhere for the aggression to go so they turn on each other.

Get a motion-activated sprinkler to scare the other cat away. The fighting with each other is definitely a problem, but if your cats start peeing indoors you're going to have real trouble.

Each one thinks that he successfully vanquished the intruder (stray) so maybe they can do the same to this other intruder (other pet cat). Normally they're fine together because they thought they had no choice but now they're like, "Hey, I'm a lot stronger than I thought! I CAN get this other guy outta here."

It's like flight or fight. They are so amped up on adrenaline/cortisol that they have to get it out somehow.

I had a similar problem years ago with a male cat hanging around and spraying by my sliding door. It distressed my strictly indoor female cat and she started urinating by the door. Ultimately, I permanently chased him away by being ready with a bucket of water or the hose and soaked him every day for three days. He never entered our yard again and my cat returned to normal. It sounds crazy writing about it now, but I was desperate.

because they are territorial

I have two M 14 yr. old strictly indoor house cats.

Recently, there has been a random, new stray cat who likes to walk by our windows or screened door & peer in.
When he/she does this, my two cats always bolt to the window/door to see him.

Then all these terrible noises ensue.
The stray alternates between loud hissing/purring while both my cats scream (sound like a Female getting murdered.)
They also hiss loudly at the stray.

When this happens - - I quickly shut the windows + screened in door.
Then immediately my own two cats turn on each other and really go at it fighting/hissing/growling/etc.
They claw at each other and leave a ton of fur in their wake.

My question is why do my cats turn on each other like this??
This is the first time ever that I have witnessed this violent behavior in them.

Thanks in advance.