Hissing works for me. It's also my body language. They see I'm alert, leaning towards them, ready to lunge in and grab the troublemaker if necessary. I'm a loon according to my husband, as I will stick my hand in between a cockatoo and CAG that have jumped each other. My birds are used to me being very hands on and physical with them so I "usually" don't get bitten; but I've also been bitten bad enough to suffer temporary nerve damage in my hand.
You have to be careful not to scare your birds, especially the grey. It's about communication of your intent, not to scare them. I escalate to the hissing. If I hiss, they know they're in BIG trouble and I'm coming over to get them. I start with, "cut it out" in a regular tone of voice; if they continue, "HEY!" pretty loud and displeased; then it gets to the "hiss" with me getting up and looking like I'm heading in their direction; if they still don't stop then I just walk over, get the troublemaker and put them away in their cage.
There's no escalation if they've actually physically engaged each other and there's imminent physical harm to either bird - that's where I'm the loon and I stick my hand in and break them apart - usually I do this while hissing as the hissing distracts them a bit from focusing on killing each other.
I had posted on another thread - I don't anthropomorphize (really, really), but using parenting techniques like they were 3 year old children works for me.




