Droll Yankees markets a variety of birdfeeders that feature Microban antimicrobial technology to fight the growth of damaging bacteria, mold, and mildew. The Yankee Flipper (two left photos) and the Yankee Whipper (two right photos) feature four seed ports with individual weight sensitive perches. The curved perch positioning encourages cardinals and small songbirds to eat, but prevents squirrels from feeding.