The Vari-Craft Bouncer has a simple, effective design that keeps squirrels, grackles, jays and starlings out of your seed supply. The four counter-weighted perches will support all of the smaller songbirds and even most cardinals but the weight of squirrels and larger birds will cause the perch to collapse to an inaccessible position underneath the feeder. The undesirable guest is ejected. Powdercoated zinc diecast top and bottom with stainless steel roof clips. 5" diameter x 18" long lexan tube provides large seed capacity while preventing squirrels from hanging off the roof and reaching the seed ports. No shocking electric charge. No batteries required. No springs.