boat tailed grackle

Several things to note that are different between the two species. Head shape is slightly different, common has a gentle slope down to the bill and boat-tailed does not. Also, common only have the blue/purple sheen on the head and neck, where boat-tailed has it on the body and not on the head. Then last and most obvious one is eye color. Commons have a yellow eye, and boat-tailed have a brown eye (Gulf Coast and Florida populations at least). Hope this helps!