Yankee Whipper® Squirrel-Proof Bird FeederKeep squirrels away from your bird feeder and save seed with the Yankee Whipper Squirrel Proof Bird Feeder. It allows the birds to eat and saves seed by keeping squirrels away. Weight sensitive perches are calibrated to collapse under approximately 2 oz. of weight Curved perch design encourages cardinals and small songbirds to eat, but prevents squirrels from feeding Length and width of tube are designed to prevent squirrels from reaching the ports