Grackles and Black Birds

This guy has been coming around the feeders for the last couple of days. Then his lighter, more brownish colored lady friend was with him and, as I was afraid of, another couple have arrived today. This is what they've done to an almost full feeder in two days - It's deceiving looking, but this feeder holds a lot of seed. Any ideas of what I might do to get rid of the Grackles?

This very distinctive brown bird has been coming by the last week or so, also. I looked her up thinking she was a sparrow of some kind - turns out she's a female blackbird? Never would have guessed!