This has been a terrible season for grackles. Unfortunately, grackles are very agile and much smaller than squirrels. We have found that most counter-weight feeders are not effective against avian pests like grackles and starlings. The best ways that I know to truly keep these pests at bay is to feed straight safflower in feeders they can land on and a good cage feeder for anything with sunflower or peanuts in it. Not all cage feeders will do the trick.