The Yankee Whipper was designed with Cardinals in mind.  Cardinals are basically ground feeders with big feet, and they hate those little perpendicular spike perches found on most tube feeders.  They have to stand sideways and turn their heads to get seed.  The graceful, curved perches of the Whipper allow Cardinals to face the feeding port while they feed.  Of course, other small and medium-sized birds can use the Whipper with ease. 

The spring-loaded perches have medium tension, allowing Cardinals and smaller birds to feed easily, but they will collapse under the weight of larger birds - Grackles and Mourning Doves.  As with all the Yankee Family of squirrel-proof feeders, squirrels are out of luck!  The Whipper is guaranteed for life against defects and squirrel damage.