A bird in a cage will be called a caged bird but Angela,the poet, wants to talk about racial equality rights.She means that black African American people used to feel caged by American white people in the 19th century.The entire theme is metaphorical ill treatment. Black people could see white people having having a normal and prosperous life but black people had restricted freedom given to them eg they could not sit on the front seats of a bus.
The answer is personification
