No squirrels or large birds like grackles can eat at this feeder as it closes as soon as their weight is on it. I have not found that cardinals use it, even with the ring, but all my other birds do except for doves as they are too heavy for the way I set it. It is reasonably easy to set the weight and I would have given it 5 stars except for two things. One, it would be helpful if there was a way to determine what weight it is set for rather than by trial and error, and secondly cleaning out the ports means a fairly major disassembly of it. I use hulled sunflower seeds in it and the 'dust' from them collects in the bottom of the feeding port so I need to clean it out every couple of times I fill it.