Another specialized feeder caters to bluebirds. Langdon said Farmer's Hardware carries two types of squirrel-proof feeders. The shock won't kill the squirrel. It's just enough to make it want to get down. Then there's one that closes from the squirrel's weight that does a good job.
Squirrels can still get on it, but they can only get a seed at a time.
An alternative to squirrel-proof feeders is something called bird pepper. The birds love it, and the squirrels hate it. One of the most specialized types of feeders is the one for hummingbirds, which uses a sweet liquid. We've got the pre-prepared mixes here. There's even a butterfly feeder, which uses nectar similar to that consumed by hummingbirds.