The title of Maya Angelou’s Autobiography, I Know Why The Caged Bird Sings (1970), is a quotation from the 1899 poem “Sympathy” by African American poet Paul Laurence Dunbar, which concludes with these lines:

I know why the caged bird sings, ah me,
When his wing is bruised and his bosom sore,
When he beats his bars and he would be free;
It is not a carol of joy or glee,
But a prayer that he sends from his heart’s deep core,
But a plea, that upward to Heaven he flings–
I know why the caged bird sings!

(the seagull reader, by Joesph Kelly)