The bird symbolism is significant in Harper Lee's To Kill a Mockingbird. Atticus Finch, who is the moral voice of the novel, is like his nomenclature, the finch, that is a quiet bird which does not like stress. It is not a noisy bird either, much like the modest and reticent Atticus.
Indigenous to Alabama, Arkansas, and Mississippi, mockingbirds do not have a song of their own, but imitate other birds'. As Atticus tells the children, they are not mean like the Jaybird who eats the eggs of other birds. But, as Miss Maudie tells the children, "mockingbirds don't do one thing but make music for us to enjoy." Thus, these birds are a symbol of innocence. As such, they represent Tom Robinson, who is kind and merely victimized by society (the bluejays). Likewise, Boo Radley is harmless and also victimized by the cruelty of the children and the "neighborhood scold," Miss Stephanie Crawford.
The mockingbird symbol and motif is also the device by which Lee unifies the two plot elements of her novel as the first part is concerned with the first mockingbird, Boo Radley, while the second part is concerned with the second mockingbird, Tom Robinson. Both harmless, they are persecuted by society.
The mockingbird idea of the novel is that there are people who do nothing but make others happy. They mind their own business, but help when necessary, as they maintain a state of "innocence" or purity. Boo Radley is persecuted by his father and society. The children mistreat him in a childlike way. Tom Robinson is the mockingbird who is truly destroyed by a world he did not create. His only sin was being nice to Mayella.
As part of a Socratic Seminar, I ask my students to not only name the mockingirds, but also the bluejays. Atticus does not see jays as the pure creatures. He tells Jem he can shoot all the bluejays he wants, just never kill a mockingbird.