How do you keep grackles from overtaking a bird feeder?

they scare all the other birds away and they are bulliesHow do you keep grackles from overtaking a bird feeder?
There are birdfeeders that screen out large birds like grackles. Small birds fit through the squares of the 'cage' and eat without interference. You will eliminate other birds like blue jays. Two feeders aren't a bad idea. One with the grackle guard and a platform or unguarded feeded.How do you keep grackles from overtaking a bird feeder?
In addition to feeders with cages, there are squirrel proof feeders that have a type of spring that is adjustable on the perch. When something heavy lands on it, the perch comes down so the squirrel or in this case grackles can't feed. I have one that is set so only small birds can perch on it without blocking the seed. The feeders are usually labeled as ';Squirrel Proof';.