The theme of the poem “The Grackle” is the negative and aggressive nature of the grackle bird. The poem portrays the grackle as a bully who intimidates and harasses other birds, using both physical and verbal aggression. The tone of the poem is critical and disdainful towards the grackle, as the speaker expresses their disapproval of its behavior. The mood of the poem is negative and judgmental, as the speaker finds the grackle to be an unpleasant and problematic bird.