At least I think it is a Boat-tailed Grackle, not a Common Grackle. This is another pair of birds that All About Birds uses a size comparison to help tell them part. Useful if you see them together, not so much on their own. They did seem to have a big tail.
These images were taken at the pond near the rookery and swamp I frequent. A group of 8 or 10 was working its way along the edge, hopping along limbs that have fallen in the water.
Both kinds are noisy, with constant calling, like their Red-winged Black bird relative. It was the iridescence that attracted me, and their repeated trips to the water. They will eat frogs, lizards, and turtles and did poke around a little in this water that has all of these but it was a bit deep for them to jump in.