No, I think I must have said that wrong. When that roo does whatever he does, there are no unbelievers. None. They ALL take cover NOW NOW NOW. All o them. Even the ones that otherwise ignore him. I just haven't heard that low call enough to know what he's doing . I know a predator call but obviously that's not the one he's doing. It's almost inaudible. But trust me, they ALL, with no exceptions, RUN for cover when he does that. None of my former roos did the same thing and got the same results. None.
More of a eeeehhh! under his breath? Different predator call for different predators. I've heard that one too.
My Sun Conures are the most reliable predator/ stranger callers. My dog pack reacts strongly to them, and you'd better not be in the way as they go out the door. The Suns believe they own the whole Polo Field that I have at my back door. Anything unusual , and they sound the alarm. They know all the usual dog walkers etc, but bring a new person, with a strange dog on the field, and they sound off. These are true flock birds ( I think designed by someone on a psychadelic trip) So their survival depends on flock diligence. Those bright colors are just too visable.