Grackles were loud and ostentatious at Beth's house while I was mowing the lawn. She pointed out to me that this is a bird, with its purplish head, different from the starling. Hers were going to the feeder. Larger birds, like robins, starlings, blue jays, are not feeder birds per se, but the grackle is pretty large.
The Cornell bird app is good. It asks you when, where, size, colors, and behavior (e.g. swimming, sitting in a tree.), then gives you a list to choose from. The references for size, in ascending order, are sparrows, robins, crows, and geese.