A very intelligent and adaptive bird, few feeders are above the grackles ability to master.  I've watched one make several attempts to eat from a feeder clearly intended for much smaller birds.  He stopped, stepped back, cocked his head to study and rethink his next step.  By the fourth try he had briefly succeeded in pulling out some food.  Just a little more practice and he could stay to eat as long as he wanted.

The most amazing thing about this procedure is that what one bird has mastered is now just as easy for the other grackles. They all took turns using only the procedure the teacher had perfected.  Obviously, the feeder challenge game is a spectator sport.  The grackle seems just as capable of learning by doing and as by being shown.

Now there was a problem.  It didn't seem that the grackle was physically aggressive towards the smaller birds at their feeders, but his mere presence drove them away. Removing the feeders meant for the larger birds and not spreading corn on the ground was not one of my finer ideas.  Instead of sending grackles further afield, it made them even more desperate to feed from smaller feeders.

Time for a new plan!  In an area somewhat removed from the original feeders, I mounted a post topped with the largest feeder we had and added two side brackets with hanging flat trays.  Here we placed regular bird seed and corn mixes.  Of course, this was the obvious answer. Every birdy's happy!

If the release of the small bird feeders wasn't enough, the squirrels (red and gray), chipmunks, and woodchucks also became happy patrons of this new cafeteria.

There was even the bonus of less mess in the main part of the yard.  Everybody wins!