We have a ton of red squirrels this spring. They seem to take over the bird feeders, hanging upside down and jumping from one to other, chasing the birds away all the while they are here.
However, one in particular has kind of won me over with his determination to "own" this one feeder. He's worked and worked at the lid for days and finally managed to get it off. I might put it back on three or so times a day, and he always gets it off again. He won, I gave up!