You'll have more problems with
white-winged doves than grackles "attacking" your bird feeders if you do set them up. Grackles are almost strictly insect eaters (though they love staking out park picnic tables, the Zoo grounds, etc. where human food scraps can be found -- french fries, etc.) The only time I have any grackles anywhere near my yard is after a rainstorm when a small flock (less than 10 birds, usually no more than 5) will sometimes land in my front or back yard and eat insects -- worms, crickets, grasshoppers, etc.
White-winged doves, on the other hand, will GORGE themselves on any and all available seed available... and the seed they don't eat they will be sure to kick out into your grass, ensuring you'll be yanking up sunflower and millet sprouts in your lawn.
At my home, the white-winged doves are also the only birds ditzy enough to frequently fly head-on into my four large downstairs windows which look out into the backyard -- it's quite a depressing sight (they leave a little, dusty "dove imprint"!), and startling if you don't see it about to happen and prepare for the "whallop" that follows, though they're tough birds -- I've only found one dead, and the rest usually keep flying or land for a minute or less to regroup.
I tried hanging things in front of the windows, and even taping each window with a huge X, but with the tape up I actually had more dove-strikes! It was like they were aiming for the X's instead of being warned off by them... maybe my doves are a suicidal flock?
