A classic children’s toy can be a fun way to keep squirrels from gorging themselves on your bird feeders. If your feeder is on a pole, attach the end of a slinky to the top and let the rest fall down the pole. One guy who tried it out says that since then, “the squirrels will try to jump onto the pole, grab the Slinky and promptly find themselves dumped to the ground.”
Ha! That must make for an amusing sight. Other techniques include switching to safflower seeds from sunflower because squirrels don’t care for it much, using PVC pipe for the poles because squirrels can’t climb it, or simply learning to live in harmony with the squirrels.
Check out the National Wildlife Federation article for more ideas.