Teuton, if you have time, available bandwidth, and a sense of humor, you might want to wonder over to Youtube and do a search on squirrel-proofing bird feeders. I did this a few months back, and discovered it is a rather popular topic. Lots of things have been tried, and lots of squirrels have found ways to defeat some great ideas. It is very entertaining. One of my favorites was someone who put up a feeder on a pole and greased the pole. The best idea I saw was to use a material for the pole that was too hard and smooth for the squirrels to get a good grip.
Squirrels ate their way into the house of a buddy of mine, so it’s open season in his yard. Most of us are anti-squirrel to show some solidarity.
We got a bird feeder that we suspended on a wire between the corner of the house and a tree, with a few yards of extra wire on each end. The squirrels would leap onto it from the arbor over the back porch, and each time I saw them there, I’d move it out another foot. Eventually it got to the point where they could juuuust reach it, smack into it and fall to the ground. This would cause some seeds to drop; once they picked themselves up, they’d eat their seeds and be on their way. I considered it a fair trade–they had to leap, smack into something, and fall to the ground to get their food. Works for me.
After several false starts, I finally found a bird feeder that is squirrel proof. They have to satisfy themselves with whatever the birds drop on the ground. The ring on the bottom will support birds, but if a squirrel manages to get onto it, the weight will cause doors to close over the feed ports.
I’d reckon that the selecting-by-squirrel’s-weight feeder which I mentioned above, would likely operate on a similar principle.