All this talk about the grackles here reminds me of what everyone still ( I suppose) says about Blue Jays in the midwest. I had six feeders there and had a special one for the Jays stocked with in the shell peanuts. They never bothered the other birds. Same with the squirrels.....they had their own corn cob feeder and never did try to get into the bird feeders. The squirrels did get a little pissed, however, every spring when the mating mallards would come through the yard and eat a meal of their corn.
Grackles were the first birds I heard on my first visit to AC, and I remember waking up wondering what sort of giant monster was on the roof......these days I barely notice them.