As soon as he steps onto the spring-loaded squirrel-guard dome, his weight pushes the dome down, closing him off from his hoped-for food supply! Then as soon as he gets off, the acrylic dome springs open again, so the birds can eat! Opening can be adjusted to keep out larger birds as well. Use any type of seed. Hanging loop. 6-1/8" dia., 8-1/2" tall overall.