Sudden Aggressive Behavior

I am so thankful for this forum! My 2 adult boy cats have been together for over 10 years with absolutely no problems. Recently (within the last 2 weeks) they have begun fighting violently! This is not play-fighting! They have been "soul mates" all this time and now I'm afraid to leave them alone as one is twice as big as the other one and I don't want to see either one injured. There has been no change to their environment, food, or other patterns in their lives so I am at a loss over this. Realizing it is the season for many female cats to go into heat, I considered whether there may be a female in the area. I do know my neighborhood has many feral cats which I can do nothing about because everyone feeds them, so I am concerned about the ferals introducing diseases, fleas, etc., that may have affected my boys. When they fight, I separate them for a time, then slowly "reintroduce" them to each other; even coaxing them with a little "nip" so they'll "make nice"! They go back to their normal behavior for a couple of days then boom, they're fighting again. The behavior is getting more frequent. If anyone has gone thru this, I'd really appreciate what you experienced and what, if any, remedy you used. My last resort will be to take them to the vet but would like to understand the behavior first. Any suggestions will be greatly appreciated! Thank you!

I have two ideas:

1. Oftentimes when friendly cats begin fighting it is due to illness in one of the cats. The aggressor may attack the victim because the victim's smell has changed due to infection or other illness. Or, the aggressor may be irritable due to not feeling well. Whenever we see a change in behavior it is wise to visit the vet to make sure they are not sick.

2. You mentioned the ferals in the neighborhood. A common kind of aggression is called "Redirected Aggression." This happens when a cat sees another cat outside. Territorial instincts are triggered and the inside cat needs to attack and chase away the outside cat. BUT, since the inside cat can't get to the outside intruder, he attacks whoever is close by. So, the inside cat will attack the closest cat (or even person) because his brain is in attack mode. Unfortunately, once the cat has attacked, it can get hardwired into thinking that it is appropriate to attack this cat, despite their being buddies for many years.

To solve problem 2, block access to windows and make sure you do not carry in the scent of the neighborhood cats. It is possible that you walk through feral spray and bring it into the house on your feet. If you think this might be the case, you might want to pull off your shoes before entering the house.

Also, spend a little money (around $20 US dollars) on a Feliway Comfort Zone diffuser. This will help calm your cats. You can find these at most pet care stores.

Finally, you may need to do a more formal separation and reintroduction of your cats, but before going that far...please take your kitties for a check-up. If you need to do this, let us know and we will describe how to make it work.

Oh....we can give you wonderful advice on the appropriate way for the neighborhood to control and care for the ferals. Visit the Ferals forum for lots of friendly advice on working with these poor cats.