Magpies love the fat balls, so they land on the feeder. Either the feeder falls off the window, or the magpies succeed in grabbing an entire fat ball and flying off with it. the feeder also falls off the window fairly often on its own. I wish the feeder had four suckers, rather than two, so it stays where it's put, and that the fat ball holders were cages, rather than just a spike. As soon as I find a feeder that works properly, this one will be going in the bin.