Squirrel Buster Plus Hang a Squirrel Buster Plus to exclude red and grey squirrels, as well as doves and grackles! Fill with carthamus (safflower) seed and exclude undesirable house sparrows as well, favoring the cardinal, while mourning doves will feed on any seed that is spilled underneath the feeder. The Squirrel Buster Plus features a cardinal-friendly ring perch. Squirrels are excluded by virtue of their weight, pulling down a "shroud" that closes the feeding ports. This squirrel-proof bird feeder is made of UV=stabilized resin, and rust-proof aluminium and stainless steel components. Furthermore, the Squirrel Buster Plus is made of detachable components, all of which are dishwasher safe, and the seeds are ventilated and keep fresher, longer.