Dear friend,
I am so sorry this is going on. It must be quite scary for you! It is called Misdirected aggression. It occurs because cats do not recognize others by sight. They depend on scent and a cats smell changes due to animal hospitals. They do not know they are friends. They "think" the other is a strange kitty from outside:
http://www.vet.cornell.edu/fhc/brochures/aggression.html
The devon may be bullying the cornish like kids pick on a weak child at school.
Above all YOU their MOM must remain calm! I know thats hard BUT they can f eel your energy.
You do not need a behaviorist for cats. They are really quite easy to understand.
They do not rationalize, nor are they capable of in depth thought or reasoning.
Everything they do is basic, logical (to them) and makes perfect sense.
In a cat heirarchy a strong kitty will always try to take over and assume the head cat position. In addition, that is always subject to changes if cat one senses weakness in cat two. Cats DO work things out in their own way and they could care less what humans (or behaviorists) think. They only respond to the energy of another animal be it feline, canine or human. Punishment is useless and counterproductive because they simply do not understand being hurt - they would just try to avoid the hurter in the future but it would not teach them anything.(except fear)
Cats do not follow a pack leader the way dogs do but they do sense their human parents energy and respond accordingly - so if you are nervous, they will be nervous. If you are stressed, they are stressed as well.
FROM CATSTER:
Use the vanilla and then let them out when you can supervise.
When the cats meet, they'll hiss and growl. But most neutered cats hate to fight and will avoid confrontation at all costs. Watch their body language. If one starts grooming, yawns or turns her head away, she's giving the other cat an opportunity to leave the "battleground" without losing face.
If anyone gets aggressive - just say SHUSH and tap him or her very lightly on the head. That lets him know (in a cat way) that the behavior is unacceptable and he will understand that feline method of correction and not be hurt, upset or insulted.The one who is probably head cat. (or thinks she is) is the resident so he must get respect.It is customary for one to submit to the other.
VERY IMPORTANT!!
Do not yell, spray water or act upset, Just immediately calmly and firmly correct her This will teach him that his aggression will not be tolerated the way another cat would treat him - except the NO! would be a hiss and the tap would be with a paw. Consistency is the key here.
Just imagine how stressed you become when they hiss - well they can feel your anxiety and it makes them nervous.
Actually if you ever watched cats in the cat room of a shelter you would see similar behavior but they eventually do work things out in an amicable fashion .Because they have to!
Get a brand new feliway plug in and rescue remedy at a pet supply to safely keep them calm.Use rescue remedy on the gums.
Please let me know how things are going. If you have questions along the way I will always be here for you.
I will help you resolve this so you can have peace in home so dont worry. Things will be fine -I promise.
Just remember to be CALM all the time!
Warmest best wishes,
Terri
Feline Healthcare Expert
Expert in feline health and behavior. 20 years experience with cats.