Wood feeders with vertical bars and feeders covered with wire mesh frustrate the larger birds. Tube feeders without trays also restrict access to small birds. Remove the perches, and you've further selected only those birds capable of clinging - finches, chickadees, titmice, and woodpeckers. Add vertical perches to tube thistle feeders, and you'll limit accessibility primarily to the goldfinches. If starlings are a problem at your suet feeder, you can discourage them by using a suet feeder with access only at the bottom.
Starlings are reluctant to perch upside down.
Chickadees and woodpeckers don't find that a problem. Species variety The species you attract is determined primarily by the seeds you offer. Black oil sunflower is the hands-down favorite of all the birds that visit tube and house type feeders. Ducks, geese, and quail will eat corn. Watch a feeder filled with a seed mix and you'll see the birds methodically drop or kick out most of the seeds to get to their favorite - sunflower.