We finally caved in and bought a squirrel-proof birdfeeder.
Let me tell you...
It was the smartest decision we ever made!
We purchased one of those birdfeeders that has an outer cage over it, and when a squirrel latches on, its own weight pulls the cage down, blocking the feeding hole.
For reference, it's similar to this:
Since we bought it, the squirrels have been chilling below the feeder, while the birds can take their share from the feeder itself.
This morning I spotted a robin, house sparrows, a brown-headed cowbird pair, a cardinal pair, a morning dove, and unfortunately some pesky grackles.
Amazingly, our feeder is grackle-free too!
I observed them trying to grasp onto the feeder, and their weight pulled the mechanism down.
Another victory for the little birds, and more losses for the annoying seed-stealers!