Round Transparent Squirrel Proof Birdfeeder This clever birdfeeder is ingeniously designed to stay open while birds are enjoying the food but the weight of a squirrel will promptly close it up. When the squirrel leaves, the spring-action opens the feeder again. The clear design allows you to enjoy bird watching and monitor food levels. Plastic and iron. Approx. 6" diameter with a 9" chain and hook.