Answer:
Both the caged bird and the individuals who wear the mask suffer from being imprisoned.
The bird is in a cage, unable to be free in nature that is so beautiful. And individuals who wear masks also feel imprisoned but in a more metaphorical way.
They are imprisoned because they cannot express their feelings and have to pretend to be happy in front of society.
The bird and the people cannot change their circumstances because they are being oppressed by someone else. The bird, because it was caged by a human and cannot escape from its cage.
And people who wear masks are trapped because of society, remember that this poem is inspired by African Americans fighting racism in a white society.
Both individuals express their pain for the desire for freedom, to be where they deserve and want to be without being oppressed by anything or anyone.